best notes ever | More Info | Notesale | Buy and Sell Study Notes Online | Extra Student Income | University Notes

Search for notes by fellow students, in your own course and all over the country.

Browse our notes for titles which look like what you need, you can preview any of the notes via a sample of the contents. After you're happy these are the notes you're after simply pop them into your shopping cart.

My Basket

Buy These Notes

You have nothing in your shopping cart yet.

Title: best notes ever
Description: easy to learn

Buy These Notes Preview

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

c
ot
sp
og
bl
y
...
blogspot
...
c
ot
sp
og
bl
y
...
blogspot
...
etc to
eduktu@gmail
...
blogspot
...
c
ot
sp
og
bl
y
...
blogspot
...
c
ot
sp
og
bl
y
...
The syllabi of chemistry taught in the name of engineering chemistry in different
engineering and technology degree colleges is of very diverse in nature
...

lo

gi

As teachers of some experience, the authors are well aware of the great value for attaching the short questions and answers as well as solutions of the numerical problems
...

no

In an effort to make the book as comprehensive as possible, a large number of topics have
been dealt with and the authors hope that this will serve the purpose of making the book useful
as a text book of chemistry for engineering degree colleges all over India
...

R Mukhopadhyay

ht
tp
:/
/k
er
al
a

Sriparna Datta

http://keralatechnologicaluniversity
...
com
(v)

C8—d:\N-engche\TITLE
...
c
ot
sp
og
bl
y
...
blogspot
...
c
ot
sp
og
bl
y
...
blogspot
...
c
ot
sp
og
bl
y
...
111

ni

1

Contents

Valency and Chemical Bonding
...
1
Application of Schrödinger Equation
...
7
Exercises
...
4367

ht
tp
:/
/k
er
al
a

3

te

ch

no

lo

Electronegativity
...
15
Dipole Moment
...
18
VSEPR Theory and Molecular Model
...
33
Short Questions and Answers
...
41
Radioactivity
...
47
Nuclear Reactors
...
53
Short Questions and Answers
...
65

4

Thermodynamics
...
70
Thermochemistry
...
83
Second Law of Thermodynamics
...
87
Short Questions and Answers
...
100

5

Reaction Dynamics/Chemical Kinetics
...
104

http://keralatechnologicaluniversity
...
com
(vii)

C8—d:\N-engche\TITLE
...
c
ot
sp
og

(viii)

6

ve

rs

it

y
...
106
Mathematical Formulation of a Second Order Reaction
...
111
Disturbing Factors in the Determination of an Order
...
120
Solved Examples
...
131
Short Questions and Answers
...
135

Catalyst
...
137
Definition
...
138
Short Questions and Answers
...
145
Exercises
...
150183

ht
tp
:/
/k
er
al
a

te

ch

no

lo

Reaction Types
...
153
Resonance
...
158
Isomerism
...
166
E and Z Nomenclature
...
171
Exercises
...
184203
Law of Mass Action and Ionisation
...
185
pH Scale
...
189
Solubility Product
...
195
Short Questions and Answers
...
202

9

Electrochemistry
...
204
Electrolysis
...
205
Relative Speeds of Ions During Electrolysis (Transport Number)
...
210
Specific Conductance
...
217

http://keralatechnologicaluniversity
...
com

C8—d:\N-engche\TITLE
...
c
ot
sp
og

(ix)

10

y
...
219
Short Questions and Answers
...
228

Electrochemical Cells
...
230
Interpretation of the Electrochemical Series
...
235
Frost Diagram
...
239
Indicator Electrodes
...
248
Solved Examples
...
256
Exercises
...
266277

ht
tp
:/
/k
er
al
a

te

ch

no

lo

gi

Introduction
...
267
The Water System
...
269
Eutectic Systems
...
273
Iron-Carbon Alloy System
...
275
Short Questions and Answers
...
277

12

Colloids
...
278
Classification of Colloids
...
280
Purification of Colloidal Solutions
...
283
Coagulation of Colloids
...
286
Application of Colloids
...
289
Exercises
...
292307
Transition Metals
...
303
Short Questions and Answers
...
307

http://keralatechnologicaluniversity
...
com

C8—d:\N-engche\TITLE
...
c
sp

ot
14

og

(x)

Metallurgy
...

bl

Introduction to the Study of Metals
...
309
Ores
...
313
Furnaces
...
320
Some Specific Examples of Extraction of Metals
...
326

Adhesives
...
329
Adhesive Strength Development
...
331
Classification of Adhesives
...
336
Exercises
...
338349

17

te

ch

no

lo

Explosives
...
339
Manufacture of Important Explosives
...
345
Short Questions and Answers
...
348

Water Treatment
...
350
Hardness of Water
...
352
Softening of Water
...
357
Hot lime-Soda Process
...
359
Ion Exchange or Demineralization
...
362
Chemical Analysis of Water
...
372
Exercises
...
377

18

Fuels and Combustion
...
379
Calorific Value
...
383
Liquid Fuels
...
blogspot
...
pm5

vi

...
415438

it

19

y
...
399
Solved Examples
...
407
Exercises
...
415
Cement
...
422
Pottery and Porcelain
...
430
Short Questions and Answers
...
437

Polymers
...
471480

ch

21

no

lo

gi

ca

Polymerization
...
445
Important Thermoplastics
...
453
Rubber
...
464
Short Questions and Answers
...
468

ht
tp
:/
/k
er
al
a

te

Paints
...
475
Lacquers
...
477
Short Questions and Answers
...
480

22

Solid State Chemistry
...
481
Fundamental Law of Crystallography
...
485
Cubic Crystals
...
492
Elements of Band Theory
...
496
Problems
...
503

23

Chromatography
...
504
Types of Chromatography
...
511

http://keralatechnologicaluniversity
...
com

C8—d:\N-engche\TITLE
...
c
sp

ot
24

og

(xii)

Instrumental Methods of Analysis
...
548560

ni

25

ve

rs

it

y
...
512
Some Terms Concerning UV
...
519
Infrared Spectroscopy
...
525
Shielding, Deshielding and Chemical Shift
...
537
Short Questions and Answers
...
547

26

lo

gi

ca

lu

Singlet and Triplet States
...
549
Photolysis
...
552
Photochemical Processes for Excited Molecules
...
556
Exercises
...
561570

ht
tp
:/
/k
er
al
a

te

ch

no

Iron
...
563
Zinc
...
564
Cobalt
...
564
Calcium and Magnesium
...
565
Electron Transport and Oxidative Phosphorylation
...
569
Exercises
...
571589
Air Pollution
...
579
Soil Pollution
...
584
Noise Pollution
...
586
Short Questions and Answers
...
589

http://keralatechnologicaluniversity
...
com

C8—d:\N-engche\TITLE
...
c
ot
sp
og
bl
y
...
The concept
of wave nature of matter came from the dual character of radiation, which sometimes behaves
as a wave and sometimes as a particle
...
These experiments conclusively proved the wave nature
of these radiations
...
Here radiation interacts
with matter in the form of photons or quanta
...

ch

A wave is specified by its (i) frequency, (ii) wavelength (λ), (iii) phase, (iv) amplitude,
(v) intensity
...
Moreover, a particle occupies a definite position in space
...

de-Broglies Equation (de-Broglies matter waves)
His suggestion was based on: as radiation like light can act sometimes as a wave and
sometimes like a particle, small particles like electron which are considered as minute particles
should also act as waves for sometimes
...

The wavelength of the matter wave is given by
h
h
λ= =
p mv
where m is the mass of the material particle, v is the velocity and p is the momentum
...

According to the wave mechanical model of the atom, an electron behaves as a standing
wave which goes round the nucleus in a circular orbit
...
(1
...

http://keralatechnologicaluniversity
...
com
1

...

bl

2πr = nλ
...

Now,

nh
mv
mvr = nh/2π

r

2πr =

it

∴

ca

lu

ni

ve

rs

or
where n = 1, 2, 3, etc
...
1
...
Other quantum
conditions can also be derived similarly, i
...
, the angular momentum is quantised
...

The New Atomic Picture

Charge Density

ht
tp
:/
/k
er
al
a

te

ch

no

lo

gi

In Bohrs atomic model, nucleus of an atom is surrounded by particles known as electrons,
which revolve in defined shells or orbits
...
e
...
These waves form stationary waves with
their nodes and antinodes
...
1
...

At nodes where the motion is practically zero, there is assumed to be a little or no charge
while at the antinodes the amount of charge is maximum
...
New wave model accepts the electron distribution to be three dimensional
...
1
...

Old Bohrs model is represented by orbits of an atom (Z = 37) (Fig
...
2) and the new wave
model is represented by a graph of spherically symmetrical electronic charge with several
maxima corresponding to the discrete K, L, M, N shells
...
blogspot
...
PM5

2

sp

2

...

bl

The dual nature of the electron implies that any precise measurement of its position
would create uncertainty in measurement of its momentum and position
...

ve

rs

∆ x
...

The above expression is known as uncertainty relation where ∆ x = change in position,
∆p = change in momentum and h = Plancks constant
...

no

lo

gi

ca

lu

Uncertainty Principle and Bohrs TheoryConcept of Probability
Bohr had postulated that electrons revolve in well defined orbits with fixed velocities
(energy)
...
On the basis of this
principle therefore Bohrs model of atom no longer stands
...
Thus the uncertainty principle which gives the wave nature of the
electron only provides probability of finding an electron in a given space
...

Schrödinger Wave Equation

te

ch

It is a differential equation capable of describing the motion of an electron
...

a = maximum displacement from mean position
...

f = frequency of vibration
...
(1)

...
(3)
+ k2 y = 0
dx 2
The above equation involves only distance as the independent variable
...
At each point along the wave in space, y varies
periodically with frequency f
...
As we
know, the total energy E of an electron is partly kinetic and partly potential
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH1-1
...
c
ot
og

ENGINEERING CHEMISTRY

h
2m(E − V)

...

h
=
mv

bl

Now, de-Broglie wavelength is given by

λ=

h2

(E − V) ψ = 0

...
For three-dimensional motion of an electron, this equation becomes,

or

...
As, p = mf is a starting
point of classical mechanics
...
(6)
h2
So, Schrödinger equation can be employed for determining the total energy of an electron
...
e
...
Like other differential equation, the Schrödinger
wave equation is also governed by boundary conditions
...
The corresponding wave function
ψ which is generally complex is called characteristic or eigen function
...
ψ* = (a ib) (a + ib) = a2 + b2, which
is real
...
But in three dimension system |ψ2|dV represents the probability
of an electron within the volume range of V to (V + dV)
...

l According to the Heisenbergs uncertainty principle, it is impossible to locate an electron
in an atom with precision but the nature of the wave function ψ is such that |ψ|2
expresses the probability of finding an electron in a definite volume of space around
the nucleus
...
The total probability of finding an electron in space extending
to infinity is expressed as follows:

z

+∞

ψ2d V = 1

−∞

where dV = dx
...
dz
...
Because of the spherical
symmetry of an atom the wave functions are most satisfactorily expressed in terms of

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH1-1
...
c
ot
og

sp

5

ATOMS AND MOLECULES

IJ
K

FG
H

IJ
K

y
...

...

sin θ
...
1
...

ni

q
m e

lu

N
E

f

gi

ca

E

lo

(a)

e

m

r

q

r
N
j

(b)

Fig
...
3

ch

no

It can be shown mathematically that each permitted solution of the wave equation (A)
i
...
, wave function ψ(r, θ, φ) can be expressed as
ψ (r, θ, ϕ) = R(r)
...
The
function Θ(θ) is function of θ depending on azimuthal quantum number (l) and magnetic quantum
number (ml)
...
The
total wave function ψ(r, θ, φ), which gives the total probability of finding an electron is called
the atomic orbital
...

The radial wave function R(r) shows the variation of wave function with r keeping θ and
ψ constants i
...
, it represents the variation of ψ in the same direction
...

For any s orbital (1s, 2s, 3s, etc
...
The angular dependence of p-orbital is
also not influenced by the principal quantum number
...

Highlight: For a small particle like an electron moving in three dimension in the field of
nucleus, the Schrödinger wave equation is

∂ 2 ψ ∂ 2 ψ ∂ 2 ψ 8π 2 m
(E − V)ψ = 0
+ 2 + 2 +
∂x 2
∂y
∂z
h2
where

m = mass of the electron,
(contd
...
blogspot
...
PM5

5

...

E = total energy of the electron,
h = Plancks constant,

it

ψ = wave function or the eigen function of the electron representing the
amplitude of the wave associated with the electron,
x, y, z = co-ordinates of the electron
...

Alternatively, the solution of the above equation produces the electron distribution in
space as well as the allowed energy state of the electron
...
Hence, the concept of quantised energy levels and quantum
numbers are the consequences of the wave theory
...
1
...

¥

no

¥

y¢[x]

|y|

n=1

L

ht
tp
:/
/k
er
al
a

0

V=0

x=0

n=3

n=2

2

n=1

ch

V

te

V

n=3

x=L

(a)

L

0

n=2
(b)

(c)

Fig
...
4

The potential energy V of the electron at the bottom of the box is constant, may be taken
as zero
...

Let the potential energy be infinite for x < 0 and x > l
...

Similarly, ψ function must be zero for all values x > l
...

A general solution of Schrödinger equation is:
ψ(x) = a sin kx + b cos kx
For boundary conditions, we have,
ψ(x) = 0 at x = 0 or ψ(0) = 0
0 = a sin 0 + b cos 0
ψ(x) = 0 at x = l

Also

or b = 0

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH1-1
...
c
ot
og

∴ a sin kl + b cos kl = 0

bl

It can only be possible when,
nπ
l
where x is called quantum number and is equal to 1, 2, 3
...

or

Substituting this value in eqn
...
E
...

n 2h 2

ni

En =

where n = 1, 2, 3
...
e
...

A few energy levels are given below:

8ml 2

ch

E3 =

9h 2

8ml 2

E1

x=0

ht
tp
:/
/k
er
al
a

te

The reason why a particle in a box i
...
, bound particle possesses
a quantised energy whereas a free particle does not, can easily be
deduced from the above equation
...
1
...

Here ∆ x = l, and the particle bounces back in the box
...
So we can write,
∆ x × ∆p = l
...

PROBABILITY DISTRIBUTION
The directional properties of an election in an orbital of the hydrogen atom cannot be represented
in one diagram
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH1-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

8

bl

These are namely (i) an angular probability distribution i
...
, how the angular position θ
varies from nucleus with respect to a fixed axis and (ii) a radial probability distribution i
...
,
how r, the distance from the nucleus does vary
...

(i) Angular probability distributions of orbitals i
...
, shapes or boundary surfaces of orbitals
gives the probability of finding an electron in a particular direction
...
e
...
This is graphically shown in Fig
...
6 below
...
1
...

ht
tp
:/
/k
er
al
a

te

ch

A p-level has an accommodation for six electrons distributed over three p-orbitals to
each value of the principal quantum number
...
In the absence of magnetic field
these orbitals are equivalent in energy content and are said to be triply degenerate
...
The different shapes are shown in Fig
...
7 below
...
1
...
e
...
Similarly, in the case of py and pz
orbitals the electron will be found along y and z axes
...
blogspot
...
PM5

8

...
1
...

y

y

it

y

z

+

–

+
x

+

+

dyz

(a)

(b)

+

lo

z
Negative
dough nut in

no

x-y plane

–
+

dz2

px2–y2

(d)

te

x

–

ch

+

z

+

x

x-y plane

dxz

y

gi

y

x

(c)

ca

dxy

–
+

ni

–

z

–

lu

–

x

ve

–

rs

z
+

y
...
These five orbitals are named as dxy, dyz, dxz, dx2 − y 2 , dz2
...
1
...

The set of the three orbitals namely dxy, dyz, dzx have their lobes lying symmetrically in
between the co-ordinated axes indicated by the subscripts to d, e
...
the lobes of dxy orbital are
pointing or lying in between the x and y axes
...

The set of two orbitals i
...
, dx 2 − y2 and dz 2 orbitals form eg set having their lobes along

the axes, e
...
The lobes of dx 2 − y2 orbital lie along the x and y axes while those of dz2 orbital lie

along z-axis
...
The probable distances of an electron are given by
radial probability distribution diagram which are given in Fig
...
9
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH1-1
...
c
ot
og

ENGINEERING CHEMISTRY

y
...
528Å)
...
The larger the
value of the principal quantum number the farther is the electron from the nucleus
as the angular probability distribution remains uneffected by the value of principal
quantum number
...

This means the electron can never be at nucleus
...
1
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH1-1
...

0

sp

10

Å

...

Give the new picture of an atom
...

Write how the uncertainty principle leads to probability approach
...

Write Schrödinger wave equation for three dimension
...

Mention the significance of ψ and ψ2
...

Apply Schrödinger wave equation for particle in one dimensional box illustrating energy
quantisation
...
Draw angular and radial probability distributions of 2s, 3p, 3d orbitals
...

1
...

3
...

5
...

7
...

9
...

11
...

13
...
blogspot
...
PM5

11

sp

11

ATOMS AND MOLECULES

...

it

2

ve

rs

Valency and Chemical Bonding

ca

lu

ni

Atoms of elements combine to form molecules of compounds
...
The electrons
remain in the K, L, M and N shells in the atoms
...

The electrons of the outermost shell of an atom take part in a chemical combination and are
called valence electrons
...
He, Ne, Ar, Kr, Rn and Xe, have eight electrons in their outermost
shells except He
...
This is a very common nature of the atoms and for this
sake, atoms either lose or gain electrons or share and this idea of electronic arrangement is the
basis for electronic theory of valency
...

ht
tp
:/
/k
er
al
a

Electrovalency: Na atom has got electronic structure ⇒ 2, 8, 1 and Cl atom has got
electronic structure ⇒ 2, 8, 7
...
This sort of transfer of
electron from one atom to the other results in the formation of Na+ and Cl ions
...
The
phenomenon can be represented pictorially as in Fig
...
1
...
2
...
Other electrovalent
compounds have been represented as follows by dot-cross method
...
blogspot
...
c
ot
+
×
×

×

2(2, 8, 18, 7)

og

×
×

= Ca + +
...

Br ×
×

×
×

×
×

...
Br
×
×

×
×

Some examples of electrovalent compounds :
×

(2, 8, 8) 2(2, 8, 18, 8)

+

S

( 2, 8 , 6 )

= 2K +

S − − (K2S)

2 ( 2, 8, 8) ( 2, 8 , 8 )

ve

2K

rs

Similarly
2( 2, 8, 8, 1)

Mg + 2F = µg ++ 2F − (MgF2)
( 2, 8) 2(2, 8)

ni

2(2, 7)

( 2, 8, 2)

lu

Highlight: Electrovalency is seen in the case of atoms with a marked difference in
electronegativity values when they combine
...
×
Cl
...
× ×
×
× Cl ×
×
×

+

×
×

×
×

×

×
×

×
×

+

...
C
...

×
×

×
×

Cl +

×
Cl ×

×
×

×
×

ch

×

ht
tp
:/
/k
er
al
a

te

×
×

×
×

×
×

×
×
Cl × Cl ×
Chlorine
molecule
×
×

×
×

×
×

×
Cl ×

×
×

×

×
×

no

Cl × +

×
×

×
×

×
×

lo

gi

When atoms, of same or more or less same electronegativity values, combine to form
molecules of a compound they share the electrons to fill up their octets in their outermost
shells
...

Examples of covalent compounds :
×
×

Carbon tetrachloride
molecule

Comparison of electrovalent and covalent compounds:
Electrovalent Compounds

(i)
(ii)
(iii)
(iv)

They are Non-directional
...

m
...
and b
...
are high
...

(v) They are soluble in polar solvents (H2O)
and insoluble in non-polar solvents
(C 6H6, CCl4)
...

Covalent Compounds
(i)
(ii)
(iii)
(iv)

They are directional in nature
...

m
...
and b
...
are low
...

(v) They are soluble in organic solvents,
generally insoluble in water
...

Co-ordinate Covalency

In covalency the bonding atoms contribute equal number of electrons to form a bond
...
The other atom contributes no electron towards the bond
...
This sort of bond formation is known as co-ordiate covalency
...
blogspot
...
PM5

13

sp

13

VALENCY AND CHEMICAL BONDING

...

bl

accepts the pair of electrons is known as acceptor atom
...
The phenomena can be represented as follows:
A
...

+

×

º (NH4)

×

H

H

Ammonium ion

×

+

ni

H

×

×

×

...
H
O
...

H
...

ve

H

rs

+

×

×

×

H

...
H
N
...

H
...

F
...
F
...

...

F

...

B

ca

Hydronium ion

te

ch

no

The attraction and repulsion powers of atoms of different elements are not same
...
In comparison, H atom has less
tendency of this sort
...
Comparative values of electronegativities of different elements
taking the electronegativity value of H as 2
...
1 below
...
1: Electronegativity values (L
...
1

2

Li
1
...
5

B
2
...
5

N
3
...
5

F
4
...
9

Mg
1
...
5

Si
1
...
1

S
2
...
0

4

K
0
...
0

Ga
1
...
8

As
2
...
4

Br
2
...
8

Sr
1
...
7

Sn
1
...
9

Te
2
...
5

6

Cs
0
...
9

Ti
1
...
9

Bi
2
...
0

At
2
...
7

Ra
0
...
blogspot
...
PM5

14

...

Partial ionic character of a covalent bond is calculated as follows:

R
S
T

1
( xA − xB ) 2
4

ni

ve

= 16(xA xB) + 3
...

When electronegativity values (x) of the two atoms A and B are same, i
...
, xA = xB, the
bond A B is 100% covalent
...
HCl
...
The relation is represented by the equation

= 43%
...
0 2
...
5(4
...
1)2

% ionic character in HF molecule

te

ch

no

lo

gi

Hydrogen atom has got only one electron
...
If the second atom is electronegative, then electron pair of the bond is
shifted towards the other atom, i
...
, F, due to its greater electron attraction power
...
In this condition, if the charged hydrogen atom comes in contact with
strongly electronegative element of the other molecules (hydrogen of HF), they are attracted
by the hydrogen (H+δ) remaining in the previous molecule and a so-called valency is formed as
if hydrogen acts a bridge between two electronegative elements
...
This type of bond is not very strong
...

Example of hydrogen bonding in HF molecules:
+d

–d

+d

–d

+d

–d

+d

ht
tp
:/
/k
er
al
a

H – F
...
H – F
...

(ii) The atomic radius of the electronegative elements should be small
...
e
...

Hydrogen Bondings
There are two types of hydrogen bonding: (a) Intermolecular (b) Intramolecular
...
HF
...
HF
...

(ii)

H¾O
Covalent
bond

H¾O
H

H¾O
H

H¾O
H

Hydrogen
bond

H

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH2-1
...
c
ot
–

N ¾O

H¾O

O

+

–

N ¾O

bl

+

O

y
...
e
...

H

te

Dipole Moment

H¾O
R

ch

no

(ii) Solubility of the molecules in water arises out of hydrogen bonding with water
molecule
...
So within a molecule two
or more positive nuclei are surrounded by electrons at different places
...

These two points in a molecule may fall at the same point or at different places in the molecule
...
e
...
The molecules containing the dipole moment
are called polar molecules
...
2
...
s
...
unit and the distance in cm unit
...
s
...
1 × 1018 esu-cm is known as 1 Debye
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH2-1
...
c
ot
og

sp

17

VALENCY AND CHEMICAL BONDING

bl

Highlights:

ni

ve

rs

it

y
...
8 D
...
e
...
8 × 1018
esu-cm
...
e
...

• Cl2, H2, CH4, C6H6, CO2, etc
...
The molecules are symmetrical,
and in those molecules centre of positive charge action and centre of negative charge
action are at the same place
...
e
...

• The dipole moment of a molecule can be calculated from the formula:

gi

ca

lu

2
2
R = µ 1 + µ 2 + 2µ 1µ 2 cos α
where, µ1 and µ2 = dipole moments of the different bonds of the molecule
...

If R is zero, the molecule becomes non-polar and if R has got a positive value the
molecule becomes polar
...

Energy released

(Electron affinity of atom A, E A )

ht
tp
:/
/k
er
al
a

te

Electron affinity is represented by the ve sign as energy is liberated in this case
...

Born-Haber cycle is represented diagrammatically with the formation of NaCl (s) from
1
Na (s) and
Cl2 (g) by direct combination to determine electron affinity of Cl atom:
2
Na(s)

+

1 Cl (g)
2 2

Q = –98
...
9 kcal
2

S = +26
...
0 kcal
(– e)
+

E = ? (+e)

NaCl(s)
Crystal
Determination of electron
affinity of Na atom
...

–

Cl (g)

Na (a)

U0 = –180
...
2 = + 26 + 28
...
4
∴
E = 90
...
blogspot
...
PM5

17

...

• Born-Haber cycle is a thermochemical cycle that can be used to calculate the lattice
energy for a compound of a metal with a nonmetal
...

• A Born-Haber cycle can also help to determine whether the bonding in a compound
is truly ionic
...
The lattice energy for
AgCl is greater than that of ionic bondings in NaCl and KCl indicating that there is
a contribution of covalent bonding in AgCl
...

gi

ca

The classical concept of covalency doesnt give any idea of the directional characteristic
of a bond and also of the bond energy
...
In this connection, two main approaches are
1
...
Molecular orbital theory
...
Both the theories admit that

ch

no

(i) A covalent bond is formed as a result of overlapping of the atomic orbitals,
(ii) When the overlapping takes place along the axes of the atomic orbitals maximum
overlapping of atomic orbitals can occur,

ht
tp
:/
/k
er
al
a

te

(iii) Maximum overlapping gives a strong bond known as sigma (σ) bond
...
2
...

(iv) Each covalent bond requires overlapping of a pair of orbitals
...

Schematic representation of the formation of some simple molecules on the basis of
valence bond theory:
(i) s-s overlapping ⇒ H2 molecule
(ii) s-p overlapping ⇒ the formation of HF, NH3, H2O molecules
(i) HF molecule

H

+

H
F

F

Fig
...
4 (a) Formation of HFmolecule
...
blogspot
...
PM5

18

...

1s
H

+

+

z

ve

rs

+

+ +

+

1s
2py

–
– –

z

+

+ +

+

2pz

it

1s
N

2px

ni

NH3 molecule

lu

Fig
...
4 (b) Formation of NH3 molecule
...
If it were the case, then bond angle in NH3 should be 90°
...
So some other concept becomes essential to explain the
formation of NH3 molecule
...

lo

(iii) Water molecule

no

x

x

1s

+

ch

+

te
ht
tp
:/
/k
er
al
a

y

y
+

+

+

+

–

+

+
z

–

–

1s
z

–

H2O molecule

Fig
...
5 Formation of H2O molecule
...
But the actual bond angle in water
molecule is 104° 27′
...

(iv) Fluorine molecule : p-p overlapping to form a σ-bond
...
2
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH2-1
...
c
ot
og

ENGINEERING CHEMISTRY

py

pz

y
...
2
...

lu

(a) Overlapping of two px orbitals along the axes leads to the formation of a sigma bond
...

no

lo

gi

ca

Hybridization: Carbon has electronic configuration: 1s2 2s2 2p2, but in CH4, C atoms form
four identical bonds with H-atom with equal energy
...
If we consider that C forms four hybrid orbitals of equal energies out of 2s
and 2p orbitals and then these hybrid orbitals overlap with s-orbitals of H-atoms along the axes,
then bond angle and bond energies in CH4 molecule can satisfactorily be explained as follows:
(ground state)

C-atom

(excited state)

te

ch

C-atom

1s

2p

2s

⇒
⇒

ht
tp
:/
/k
er
al
a

Now this one s-orbital and three p-orbitals of a carbon atom mix to give four hybrid
orbitals of equal energies, the axes of hybrid orbitals are directed towards the vertices of a
regular tetrahedron (Fig
...
8)
...
2
...

Now these four sp3 hybrid orbitals overlap along the axis with s-orbitals of four H-atoms
to form a CH4 molecule forming four covalent bonds of same energies
...
blogspot
...
PM5

20

sp

20

...

bl

H

C

it

H
H

rs

H

Fig
...
9 CH4 molecule
...
The hybrid orbitals lie in a plane
and the axes are directed towards vertices of an equilateral triangle and so, bond angle in this
case is 120°
...

H

H
C

C

H

p-bond

s-bond
H

p-bond

Fig
...
10 Ethylene molecule
...
2
...

Highlights:
• Ethylene molecule contains five sigma bonds
...
Residual 2p orbitals of each sp2 hybridised C-atom overlap
laterally to form a π-bond (Fig
...
10)
...
blogspot
...
PM5

21

sp

21

VALENCY AND CHEMICAL BONDING

...

bl

In boron trifluoride the sp2 hybrid orbitals of B atom overlap with p orbitals of three F
atoms along the axes to form three sigma bonds (Fig
...
11)
...
2s and 2p hybridise electrons to produce three sp2 hybrid orbitals
directed towards the vertices of an equilateral triangle
...
2
...
(Another example of sp2 hybridization)
...
In the excited state of C-atom
there are two hybrid orbitals (sp) and two unchanged p-orbitals
...
Then two C-atoms
possess total four unchanged p-orbitals
...
So triple
bond of acelylene molecule contains one σ-bond and two π-bonds
...
2
...

In BeF2 molecule the central atom Be has electronic configuration ⇒ 1s2
...
Since, there is no unpaired electron, the Be atom cannot form any covalent bond
...
blogspot
...
PM5

22

...

bl

In the excited state one of the 2s2 electrons jumps to 2p-orbital before forming any bond
...
2px1 2py0 2pz0
...
These two hybrid orbitals next overlap with p orbitals
of two F-atoms along the axes making BeF2 a linear molecule (Fig
...
13)
...

180°
F

F
Be

F

ch

Fig
...
13 Structure of BeF2 (example of sp hybridisation)
...
In this type of bonding,
charge cloud exists symmetrically
...
In this type of bonding, the overlapped charged
cloud is parallel to internuclear axis
...

Hence, the π-bonds open easily and take part in the chemical reactions
...

Table 2
...
54

1
...
21

1
...
10

83

144

196

38

225

Bond energy (Kcal)

dsp2-hybridization
In this type of hybridisation one s-orbital, two p-orbitals (px and py) and one d-orbital
( dx 2 − y2 ) mix to give four equivalent hybrid orbitals, axes of which are directed towards the

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH2-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

24

bl

corners of a square
...
3)
...

dsp 3 or sp3d hybridization

In this type of hybridization dz 2 orbital and one s-orbital and three p-orbitals mix to give

ni

ve

rs

it

five orbitals (Fig
...
14)
...
The hybrid
orbitals consist of one group of two equivalent oppositely directed orbitals and the second group
of three equivalent orbitals
...
2
...

s
py

gi

pz

ca

lu

px

2

dz

3

dsp

lo

Fig
...
14 sp3d hybridization
...
The shape of the molecule is trigonal bipyramidal (Fig
...
15)
...
2
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH2-1
...
c
ot
og

d2sp3 or sp3d2 hybridization
3d

3p

it

S-atom in ground state Þ

y
...

F

gi

F

lo

S
F

no

F

F

Table 2
...
2
...

No
...
When the central atom
contains one or more lone pairs (lp) of electrons in the valence shell with bond pairs (bp) the

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH2-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

26

lo

gi

ca

lu

ni

ve

rs

it

y
...
The orbital containing lone pair of electrons in the valence shell
occupies more space and the lone pair-lone pair repulsion is greater than the lone pair-bond
pair repulsion
...
e
...
repulsion
...

This is the basis of Valence Shell Electron Pair Repulsion (VSEPR) theory
...
Central atom surrounded by two bonding pairs:
The two bonding pairs remain as apart as possible
...
Example:
BeF2
...
The central atom surrounded by three bond pairs: They remain as apart as
possible and the bond angle is 120°
...
Central atom surrounded by four bond pairs:
Example methane
...

In all the above cases there were only bond pairs in the
molecules and the molecules have a regular geometry
...
Molecule containing lone pair and bond pair:
Example ammonia molecule:
The geometry of the molecule is distorted tetrahedron
...

and one hybrid orbital contains lone pair of electrons
...
Here lp-bp repulsion is
greater than the bp-bp repulsion
...
2
...

H

107°
H
H

Fig
...
17

H2O molecule:

Here O-atom is sp 3 hybridized and only two H-atoms occupy the two corners of a
tetrahedron
...
Overlooking those two corners of the tetrahedron the
H2O molecule becomes V shaped (Fig
...
19)
...
p
...
96
b
...

l
...

O

H

O

Å
105

°

b
...
2
...

Fig
...
19 V-shaped water molecule
...

The bond angle becomes more reduced (Fig
...
20)
...
blogspot
...
PM5

26

...
O

y
...

...
2
...

ni

NH3 and H2O molecules are examples of distorted molecules due to the presence of
lone pairs in the hybrid orbitals and lp-bp, lp-lp repulsions
...
So melting of such solids occurs when the highly ordered arrangement
of particle in the crystalline lattice changes to the more random arrangements (characteristic
of a liquid)
...
So energy requirement for melting is less
compared to ionic compounds
...

–

–

displaying dipole-dipole interaction
(in HCl molecule)

+

ht
tp
:/
/k
er
al
a

As a result of dipole-dipole interaction, polar molecules are held to each other more
strongly than non-polar molecules (purely covalent molecules)
...

There must be some forces between the molecules of a non-polar compound
...
Such attraction is known as van der Waals force of attraction
...
They act only between the portions of different molecules
that are in close contact, i
...
, van der Waals forces are weak intermolecular forces which are
responsible for weakest attractions between nonpolar molecules
...
This is called van der Waals radius
...
Thus, we can say, non-bonded atoms
strongly resist crowding
...

Molecular orbital theory [linear combination of atomic orbitals, LCAO]
Homonuclear diatomic molecule:
Let, two H-atoms designated by HA and HB containing two 1s-atomic orbitals overlap to
form M
...
Then expression for two molecular orbitals (M
...
) will be one bonding (φB) and the
other antibonding (φA):

http://keralatechnologicaluniversity
...
com

C-8\N-ENGCHE\ECH2-2
...
c
ot
og

ENGINEERING CHEMISTRY

y
...

+

+

...

...

it

...
2
...
2
...

ca

Linear combination of 1s-atomic orbitals (σ-symmetry) of two H-atoms to give bonding
and antibonding molecular orbitals (σ-symmetry)
...
2
...
O
...

Energy level diagram (Fig
...
22) illustrating the formation and relative energies of
∗
σ1s (bonding) and σ1s (antibonding) molecular orbitals resulting from the combination of two
1s-atomic orbitals on two H-atoms in H2 molecule
...
2
...

http://keralatechnologicaluniversity
...
com

C-8\N-ENGCHE\ECH2-2
...
c
ot
og
–
+

p2* 2p

it
rs

–

+

fA(Antibonding)

+

E

–

y
...
2
...
2
...

y

ch

no

z

lo

gi

ca

lu

Linear combination of two 2pz orbitals to form πz2p (bonding) and πz2p* (antibonding)
molecular orbitals (π-symmetry)
...
2
...
O
...
O
...
O
...
B
...
A
...
O
...
B
...
of electrons in bonding molecular orbitals
...
A
...
of electrons in antibonding molecular orbitals
...
blogspot
...
PM5

29

sp

29

VALENCY AND CHEMICAL BONDING

...
4
B
...

Significance

y
...

unstable and does not exist
...

rs

ve

it

0

ve

*Greater the value of B
...
greater is the stability of the molecule
...
Thus molecular orbital posses3ing the lowest energy will be filled first and that possessing
the highest energy will be filled up in the last
...

(iii) According to Hunds rule of maximum multiplicity, if there are two molecular orbitals
having the same energy (i
...
, degenerate molecular orbitals), the electrons will first
fill them singly and when both of them have been filled singly, pairing of electrons
will occur
...
In a similar fashion πy*2p and πz*2p antibonding degenerate molecular
orbitals are filled just like degenerate bonding orbitals
...
2
...

2s

s(sp)

2

Fig
...
27 Molecular orbital diagram
allowing s-p interaction
...
In N2 molecule there will be all
total 14 electrons of which 4 will be in the K shells which is denoted by KK
...
blogspot
...
PM5

30

sp

30

...

og

bl

So, the electronic configuration of N2 molecule will be
KK(σ2s2) (σ*2s2) (σ2p2) (πy2p2) (πz2p2) [KK denotes (σ1s2) (σ*1s2)]

pz*2p

2px 2py 2pz

A
...

rs

py*2p

2pz 2py 2px
py2p

pz2p

ve

A
...

it

M
...

s*2p

ni

s2p

lu

E

ca

s*2s

B
...
= 8 – 2 = 3
2
N2 molecule has triple
bond (N º N)

2s

lo

gi

2s

no

s2s

Fig
...
28 M
...
diagram for N2
...
2
...

B

B2

Fig
...
30 Molecular orbital diagram of
B2 (with s-p interaction)
...
blogspot
...
PM5

31

B

sp

31

VALENCY AND CHEMICAL BONDING

...
2
...

ch

no

Fig
...
31 Molecular orbital diagram
of O2 (without s-p interaction)
...

s*sp)2

p*2py p*2pz

s*2px

p*2py p*2pz

s2s
O2

bl

• Electronic configuration of B2 molecule:
KK(σ2s2) (σ*2s2) (σ2p2)

¯
2pz 2py 2px

• Electronic configuration of O2 molecule:

ht
tp
:/
/k
er
al
a

te

KK(σ2s2) (σ*2s2) (σ2p2) (πy2p2) (πz2p2) (π*2p1) (πz*2p1)
y
s*sp)2

p*2py p*2pz

s*2px

p*2py p*2pz

¯
2pz 2py 2px

¯
2pz 2py 2px

¯
2pz 2py 2px

2pz

¯
2py 2px

¯

¯ ¯
p2py p2pz
¯
s2px

s(sp)2

p2py p2pz

¯
s*2s

¯
s*(sp)1

¯

¯

¯

¯

2s

2s

2s

2s

¯
N

¯

s2s
NO

s(sp)1
NO

O

Fig
...
33 Molecular orbital diagram
of NO (without s-p interaction)
...
2
...

http://keralatechnologicaluniversity
...
com

C-8\N-ENGCHE\ECH2-2
...
c
ot
og
bl

[Energy level diagram for heteronuclear diatomic molecule]

σ*(sp)1

π(2p)

σ(sp)2

B2

↑↓

↑↓

↑

C2

↑↓

↑↓

↑↓

↑↓

N2

↑↓

↑↓

↑↓

↑↓

↑↓

O2

↑↓

↑↓

↑↓

↑↓

↑↓

CO

↑↓

↑↓

↑↓

↑↓

↑↓

NO

↑↓

↑↓

↑↓

↑↓

π*(2p)

ve

rs

↓

σ*(sp)2

it

σ(sp)1

y
...
5: Electron Distribution in Molecular Orbitals of some
Simple Molecules shown in above M
...
diagrams

lu

ni

↑

↑↓

unpaired
electrons
2
0
0

↑

2
0

↑

1

ca

Molecule

Aromatic Character

gi

Organic compounds have been classified into two broad subdivisions: (i) aliphatic and
(ii) aromatic
...
Aliphatic compounds are mainly open chain compounds
...
Aromatic
compounds a2e benzene or the compounds that resemble benzene in chemical behaviour
...

(ii) Heat of hydrogenation of benzene is lower than that expected
...

The idea of resonance could explain all the three above anomalies and established the
structure of benzene as put forward by Kekule
...
blogspot
...
PM5

33

sp

33

VALENCY AND CHEMICAL BONDING

...

• The idea of resonance explains six identical bonds in benzene, which is a new type of
bond, a hybrid bond or benzene bond, i
...
, it is an intermediate in length, (1
...

• Benzene is more stable than expected
...

• As a result of this resonance stabilisation, benzene possesses chemical properties
that are not intermediate between compounds containing single or double bond
...

• We see that addition will lead to a less stable product by destroying the resonance
stabilized benzene ring system
...
6 Kcal mole1 to be converted into cyclohexadiene
...

ca

Orbital Picture of Benzene

Benzene is a flat molecule, as its six carbon atoms are sp2 hybridised
...
And there still
remains six electrons in the six p-orbitals with two equal lobes, one lying above the plane and
the other lying below the plane of paper
...

(i) Only s-bonds are shown
...
2
...
When overlapping is not restricted between two nuclei
and it occurs between more than two nuclei, the phenomenon is known as delocalisation
...
This delocalisation energy is
frequently used instead of resonance energy
...
(2
...

p-clouds

Benzene ring

p-clouds

Fig
...
36 Delocalised π clouds in benzene
...
blogspot
...
PM5

34

...

bl

So, necessary and sufficient conditions for aromaticity are:
(i) The molecule should be cyclic and flat
...

(iii) The π-cloud must contain a total of (4n + 2) π electrons where n = 0, 1, 2, 3, etc
...

Benzene has six π-electrons (known as aromatic sextet)
...
Benzene molecule is flat
...

ve

Highlights:

ni

• Benzenoid aromatic compounds: naphthalene (n = 2), anthracene (n = 3), phenanthrene
(n = 3)
• Heterocyclic compounds: pyrrole (n = 2), pyridine (n = 2) etc
...

gi

lo

antenacene (Anthracene)
14 p electrons
phenanthrene
14 p electrons

no

naphthalene
10 p electrons

ca

Benzenoid aromatic compounds:

(+)

ht
tp
:/
/k
er
al
a

N
H
pyrrole
6 p electrons

N
pyridine
6 p electrons

:

:

te

ch

Non-benzenoid aromatic compounds:

(–)
cyclopentadienyl
anion
6 p electrons

tropylium ion
6 p electrons

SHORT QUESTIONS AND ANSWERS

Q
...
What is a molecule?
Ans
...

Q
...
What is a chemical bond?
Ans
...

Q
...
Mention the types of bonds
...
Most important types are: (i) Electrovalent, (ii) Covalent and (iii) Co-ordinate
bonds
...
4
...
Such a bond is formed by complete transfer of electrons from one atom to the
other
...
Thus ions are formed
...

http://keralatechnologicaluniversity
...
com

C-8\N-ENGCHE\ECH2-2
...
c
ot
og

ENGINEERING CHEMISTRY

Sodium atom
(2, 8, 1)

×

Na+

Þ

Cl ×
×
××

Chloride atom
(2, 8, 7)

Ans
...
Cl ×–
×
×

+

××

Sodium ion
(2, 8)

Chloride ion
(2, 8, 8)
–

+

××
×

Calcium atom
(2, 8, 8, 2)

F

××

Ca++

Þ

×
×

+

Calcium ion
(2, 8, 8)

two fluoride
ions (2, 8)

ve

(2, 7)

...
×
×F×
××
×

rs

Ca :

F×
×
××

it

××
×

y
...
5
...

Na
...
6
...
Covalent bond is formed when two atoms participating in bond formation share
equally their electrons to produce a molecule of an element or a compound
...
Cl :

: :
: :

lu

Q
...
Give examples of single, double and triple covalent bonds by dot and cross diagrams
...
(i) Single covalent bond
...

Þ

Cl—Cl

lo

×

Þ

H
H—C—H

no

+ 4H

H

...

H

gi

Single bond

...
C
...

H

te

...

(b) 2
...

+ 4H

Þ

×

(iii) Triple covalent bond
...
N

: :

: :

(a) N
...

H C ::C× H
:
:

: :

: :

(a) O:

Þ

...

Þ

N::N

...

...

Þ H—C º C—H
(b) 2
...
+ 2H × Þ
H×C:: C×H

...

Q
...
How are the atoms held together in a covalent bond?

Ans
...

Attraction

+

+

Proton in
nucleus

Shared electrons

Fig
...
37 (a) Forces of attraction during H2 molecule formation
...
blogspot
...
PM5

36

sp

36

...
9
...

bl

Ans
...
e
...
e
...
,
HH, O = O, ClCl, BrBr, etc
...
e
...
,
H+δ → Clδ

ni

ve

Q
...
What is the special feature of a covalent bond?
Ans
...
(b) Molecules have a definite shape because covalent bonds have a definite length
and direction
...
11
...
The covalent radius of an element is half the bond length
...
Covalent radius of an atom is half of the distance between the
nuclei of two like atoms bonded together by a single covalent bond
...
104 nm Cl2

Bond length
Þ 0
...
037 nm H2

ht
tp
:/
/k
er
al
a

Fig
...
37 (b) Forces of attraction during H2 molecule formation
...
114 nm
van der Waals radius » 0
...
van der Waals
radii determine the effective size of a molecule
...

Fig
...
37 (c) Covalent and van der Waals radii for bromine
...
12
...

Ans
...

Q
...
What is the special feature of a coordinate bond?
Ans
...
The
coordinate bond is indicated by an arrow to express this unequal sharing
...
blogspot
...
PM5

37

sp

37

VALENCY AND CHEMICAL BONDING

...
14
...

OP
PP
PP
Q

it

LM
MM
MM
N

H
H


H  N : + H+ ⇒ H  N → H


H
H

og

ENGINEERING CHEMISTRY

ve

rs

Ans
...
of different atoms whereby maximum overlapping of orbitals
is possible
...
15
...
π-bond is formed by sideway overlapping of mainly p-orbitals of different atoms
...
16
...
A single bond is always a σ-bond
...

Q
...
What do you mean by dipole moment?

µ = dipole moment,

ch

where,

no

lo

gi

Ans
...
Mathematically dipole
moment is expressed as:
µ=e×d

te

e = magnitude of charge separated in esu,
d = distance in cm
...
18
...
Bond energy (or enthalpy) is the mean value of bond dissociation energies (or
enthalpies) (D) used for approximate calculation estimating the enthalpy changes for the
reaction
...
Energy is needed to break covalent bonds
...

HCl (g) ⇒ H(g) + Cl(g) ∆H ⇒ + 432 kJ mol1
...
19
...
In HOH (g) molecule, the energy needed to break the first OH bond is
498 kJ mol1, the energy needed to break the second OH bond is 428 kJ mol 1
...

Q
...
Calculate the CH bond energy in CH4 molecule
...

CH4 → CH3 + H°
CH3 → CH2 + H°
CH2 → CH + H°
CH

→ C + H°

D ⇒ 102 Kcal mol1
D ⇒ 105 Kcal mol1
D ⇒ 108 Kcal mol1
D ⇒ 83 Kcal mol1
Total D ⇒ 398 Kcal mol1

http://keralatechnologicaluniversity
...
com

C-8\N-ENGCHE\ECH2-2
...
c
ot
og

CH bond energy in CH4 is mean value of D values i
...
,

bl

398
= 99
...

4
Q
...
What do you mean by bond length?
Ans
...
For the same two atoms triple bonds are shorter than double bonds which, in
turn, are shorter than single bonds
...

0
...
134nm

rs

it

y
...
120nm

B

B

ve

B

–d

ca

+d

lu

ni

Q
...
What do you mean by electronegativity?
Ans
...
The stronger the pulling
power of an atom, the higher its electronegativity
...

H ¾Cl
¯

gi

polar bond
...
23
...
The bonding in a compound becomes ionic if the difference in electronegativity of
the two bonded atoms becomes so large that the more electronegative atom can remove
completely the electron from the other atom
...

ht
tp
:/
/k
er
al
a

te

ch

Q
...
Give the conception of a bonding molecular orbital
...
The bonding molecular orbital is a region in space where the probability of finding
the bonding electrons is maximum
...
In a simplified form, it may be stated that molecular orbitals
(M
...
) are obtained by the overlapping of atomic orbitals of the atoms linked by a covalent
bond
...
O
...
O
...
2
...
23) i
...
, M
...
is produced by addition of two
atomic orbitals (φB = ψA + ψB)
...
25
...

Ans
...
But in this case, φA results from subtraction of the two atomic
orbitals (φA = ψA ψB) i
...
, by the overlapping of + regions of the atomic orbitals (see Figs
...
21 and 2
...

Q
...
Interpret the idea of bond order
...
Bond order (B
...
) is given by the expression,
Nb − N a
2
⇒ number of bonding electrons
...
O
...

Higher the bond order, stabler is the molecule
...

http://keralatechnologicaluniversity
...
com

C-8\N-ENGCHE\ECH2-2
...
c
ot
sp
og
bl
y
...
blogspot
...
etc to
eduktu@gmail
...
blogspot
...
c
ot
og

ENGINEERING CHEMISTRY

Q
...
What is hybridisation of atomic orbitals?

rs

Ans
...

Q
...
What do you mean by hybrid orbitals?

it

y
...
The intermixing the atomic orbitals of slightly different energies so as to redistribute their energies and to give a new set of orbitals (known as hybrid orbitals) of equivalent
energies and shape is known as hybridisation
...
28
...

lu

ni

ve

Ans
...

Q
...
Calculate the bond orders of: (i) H2O, (ii) H2+, (iii) He2+, (iv) He2 and interpret the
result
...
(i)
B
...
= b
=
=1
2
2
H-atoms are held together by one covalent bond
...
Here the number of bonding electrons exceeds the number
of electrons in antibonding orbital
...
O
...
Here, the number of electrons in s-orbital is greater
than the number of electrons in s*-orbital
...
O
...
The
molecule does not exist
...

Q
...
O2 molecule is paramagnetic
...

Ans
...
O
...
According
to Hunds rule two unpaired electrons fill the degenerate (orbitals of same energy) πy*2p and
πz*2p orbitals (see Figs
...
31 and 2
...
That is why, O2 molecule is paramagnetic
...
32
...

+δ

B
...
⇒

+δ

+δ

+δ

Ans
...
H− F − δ
...
H− F −δ
Due to hydrogen bonding, there is molecular association in HF and effective molecular
weight of HF is high and that is why its volatility is less and it is liquid whereas in HCl
molecule there is no hydrogen bonding because Cl is less electronegative than F and atomic
radius of Cl is greater than that of F
...

http://keralatechnologicaluniversity
...
com

C-8\N-ENGCHE\ECH2-2
...
c
ot
og
bl

Q
...
Explain H2O is a liquid and H2S is a gas
...

it

y
...
31 above
...
34
...
formula, C2H6O
...

ve

H

H—C—O—C—H

ni

H——O– – –H——O– – –H——O
C 2H 5
C 2H 5
C 2H 5

rs

H

Ans
...
But there is no H-bonding in dimethyl ether molecule
as H here is not attached to O-atom
...

Q
...
The density of water is greater than that of ice
...

O
Covalent bond
Ans
...
And each oxygen
H
atom contains two lone pairs
...
By X-ray crystallography, it has been
established that in a crystal of ice, a molecule of water is
surrounded by four water molecules and every molecule of
water form hydrogen bonds giving a tetrahedral structure
...
Due to tetrahedral structure, there is some void
space in ice
...
And the water molecules are hydrogen bonded in a
chain
...

H

H

Hydrogen
bond

O

O
H

H

H
O

O
H

H

Fig
...
38 H-bonding in ice
...

What is hybridisation? Give different types of hybridisations with examples
...

Explain sp, sp2 and sp3 hybridisations with examples
...

Write a note on co-ordinate bond
...

Give the state of hybridisation, bond angle and shape of the following molecules:

5
...

(a) Explain the structure of benzene
...

6
...

7
...

8
...

http://keralatechnologicaluniversity
...
com

C-8\N-ENGCHE\ECH2-2
...
c
ot
og

ENGINEERING CHEMISTRY

sp

42

ht
tp
:/
/k
er
al
a

te

ch

no

lo

gi

ca

lu

ni

ve

rs

it

y
...
Explain inter and intramolecular hydrogen bonding with examples
...
(a) Explain hydrogen bonding
...
(c) Explain sp3hybridisation
...
What is VSEPR theory of molecular model? Explain with suitable examples
...
What is dipole moment? How is dipole moment of a molecule calculated?
13
...

14
...

15
...

State the nature and formula of the compound so formed
...

16
...

http://keralatechnologicaluniversity
...
com

C-8\N-ENGCHE\ECH2-2
...
c
ot
sp
og
bl
y
...
It is
quite obvious that the conventional energy sources, such as coal, petroleum will be exhausted
in near future
...
The idea of exploiting nuclear energy came after the discovery of
radioactivity
...

no

RADIOACTIVITY

ht
tp
:/
/k
er
al
a

te

ch

Becquerel in 1896 observed that uranium or its compounds emit a kind of rays spontaneously
...
He named this phenomenon of emission of spontaneous
radiation by uranium as radioactivity
...
As compounds of those elements exhibit
radioactivity, so it can be said that radioactivity is a nuclear phenomenon
...
Radioactivity is an irreversible process and emits
more heat than that of any of the chemical processes (109 cal mol1)
...
A comparative
study of the rays emitted during radioactive disintegration is displayed in the following table
...
1: Comparison among α, β, and γ Rays
α-Rays
(i) Streams of positively
charged particles
which are merely
nuclei of He atoms,
each consisting of 2
protons
and
2
neutrons
...

(i) It is similar to Xrays and neutral
in nature
...

(ii)

1e°

or

1 β°

or β
...
)

http://keralatechnologicaluniversity
...
com
43

...
m
...

(iii)

(iv) Charge

(iv) Possess
positive
charge of 2 units
= 9
...
s
...
or
3
...

(iv) Possess negative
charge of 1 unit
= 4
...
s
...
or
1
...

it

1
of hydrogen
1836
atoms or 0
...
m
...

og

ENGINEERING CHEMISTRY

(v) Velocity

(v) Nearly 1/10 the speed
of light or 20,000 to
30,000 km per sec
...
36 × 108 to 2
...

(v) Nearly same as
light 3 × 108 m/sec
...

bl

(iii) No mass (0)

ni

ve

rs

(iv) No charge (0)

lu

(vi) Maximum

ca

It has been observed that heavier elements in which neutron-proton ratio (N/p) exceed
1
...
These nuclei are unstable and emit spontaneously α, β, or γ-rays to give
daughter elements
...
Nuclei with 84 or more protons are radioactive
...
Nuclei containing 2, 8, 20, 50, 82 and 126 protons or neutrons are more stable than
other nuclei containing different number of protons and neutrons
...

3
...

240

120

80

40

0

10

30
50
Atomic number, Z

70

90

Fig
...
1

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH3-1
...
c
ot
og

sp

45

NUCLEAR CHEMISTRY

rs

it

y
...
3
...
The graph is
more or less linear
...
e
...
As the
difference of Z and A increases the nucleus becomes totally unstable
...

Radioactive Decay

ve

The radioactive decay follows an exponential law
...
e
...

The negative sign indicates that with passage of time t the number of atoms decreases
...
e
...
eλt

∴

When M0 = original mass and M = mass at time t, the equation is
M = M0
...
3
...

t=T
t = 2T
t = 3T

Time t

Fig
...
2 Decay curve of radioactive substances
...
blogspot
...
PM5

45

...

log e 2 0
...

λ
λ
The above equation is a relation between half life (T) of a radioactive element and its
disintegration constant (λ)
...
Half-lives for radioactive isotopes can be as short as a fraction of a second or as long as
millions of years
...
The curie is defined as that quantity of any radioactive
substance which gives 3
...
The curie is a very large unit
...

Radioactive Disintegration Series

ch

no

lo

Number of naturally occurring radio isotopes is about forty
...
The series are 4n or Thorium series; 4n + 2 or
Uranium series and 4n + 3 or Actinium series
...

232
90 Th

te

In the 4n series starting element is

ht
tp
:/
/k
er
al
a

disintegration it produces ultimately

and through a chain of successive

208
82 Pb
...

82 Pb

and end product is

207
82 Pb
...
It starts

with

237
93 Np

and ends at

200
82 Bi
...
e
...
When a β-particle is emitted the daughter element formed shifts to one
column forward (right side) in the periodic table i
...
, atomic number of daughter element is
increased by one unit
...
blogspot
...
PM5

46

sp

46

...

1

it

+ 4 He →
2

This phenomenon is known as Artificial Radioactivity
...

to a radioactive atom, e
...
if we bombard 27 Al with an alpha (α) particle, we get radioactive
13
phosphorus which is ultimately converted to silicon
...
m
...
=

ca

lu

ni

ve

Atomic Mass Unit
Masses of atoms are usually expressed in atomic mass units (a
...
u
...
m
...
=
6
12
1 12
1
g=
g
×
So,
1 a
...
u
...
023 × 1023

1

6
...
66 × 10 −24 g
...
The famous equation in this regard is
E = mc2
where E = energy ; c = velocity of light
...

Highlight:

E = mc2
= 1 × (3 × 1010)2 g cm2 sec2
= 9 × 1020 g cm2 sec2
= 9 × 1020 ergs
= 9 × 1013 joules
...

Mass-Energy conversion factor
We know that,
1 eV = 1
...

So,
1 MeV = 1
...
m
...
= 1
...

∴

1 a
...
u
...
6 × 9 × 10 20
1
...

Nuclear Fission
In 1939, German scientists Hahn and Strasman bombarded uranium atom with neutrons and
obtained two elements with atomic numbers 56 and 36
...
blogspot
...
PM5

47

...

92
56
36
This phenomenon of splitting a nucleus into two approximately equal fragments is called
nuclear fission or simply fission
...

This process of repeated fission is known as chain reaction (Fig
...
3) and as a result it can
generate a huge amount of energy, 1 g of U-235 will generate 2 × 107 kcal, and this amount of
energy will be generated within 106 second
...
This nuclear fission reaction is
the principle of an atom bomb
...

bl

235
92 U

ht
tp
:/
/k
er
al
a

te

ch

no

lo

gi

ca

lu

ni

ve

1
0n

(Secondary neutrons)

Neutrons
Fission Fragments

235
92U

Fig
...
3 Chain reaction as a result of bombardment of 92U235 with one
neutron and perfission three secondary neutrons are released
...
A small fraction of mass is lost and is
converted to energy according to the equation: E = mc2
...

235
92 U
1
0n

Initial masses
⇒
235
...
m
...

⇒

1
...
m
...

236
...
m
...

141
56 Ba
92
36 Kr
1
30 n

Final masses
⇒
140
...
m
...

⇒

91
...
m
...

⇒

3
...
m
...

235
...
m
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH3-1
...
c
ot
og

sp

49

NUCLEAR CHEMISTRY

bl

So, the mass lost is 0
...
m
...
, which is equivalent to an energy of 0
...

y
...
2 × 1013 J, which is sufficient to supply energy at the rate of 2
...

ni

ve

To utilise the energy released during the fission, we are to control the chain reaction to
get the heat energy according to necessity
...
So, fission
reaction is retarded and thereby controlled and the heat generated is being absorbed by molten
NaK alloy and this heat is utilised in generating steam for thermal power
...
e
...
This phenomenon is known as atomic fusion
...

+ 2 H → 4 He + Energy
1
2
2 × 2
...
00389
∴
∆m = 0
...
m
...

which is equivalent to 0
...
6545 MeV
...
But it is believed
that such condition is attained for preparing thermonuclear bombs such as hydrogen bomb
...

1
1
2

Mass Defect and Binding Energy
After the discovery of isotopes, Aston examined the atomic weights of various elements
and concluded that the atomic weights of all the elements would be a whole number
...
Besides
that, the atomic weights of the different elements depend upon another factor: in a
...
u
...
The calculated
mass (M) and actual weight (A) is determined considering the contribution for the presence of
isotopes
...

For a 7 Li atom, the atomic weight will be
3
3 × 0
...
00758 + 4 × 1
...
0601058 a
...
u
...
01818 a
...
u
...
0601058 7
...
0419258 a
...
u
...
blogspot
...
PM5

49

...

bl

When protons and neutrons unite a small fraction of mass is converted to nuclear binding
energy, and this is the reason for mass defect
...
0419258 × 931 = 39
...

When mass defect is divided by mass number, a fraction is obtained which is known as
packing fraction (f)
0
...
81
Therefore, packing fraction is average mass defect for any particle
...
A small value of packing
fraction indicates greater stability of the nucleus, a higher value indicates looseness of packing
of protons and neutrons in the nucleus and as such lower stability of the atom (Fig
...
4)
...
3
...
mass number (A)
...
In other words it is a device where controlled
nuclear fission of 235U, 233U or 239Pu and also chain reaction takes place and produces, heat,
neutrons and radio-isotopes
...

The mechanism for heat generation: In the nuclear reactors due to the fission fragments
which move at high speed because they take bath in a dense mass of metal, they are rapidly
slowed down and brought to rest due to collison with other atom of the metal
...

Nuclear reactors are of various types depending on their neutron spectrum, construction,
composition and the purpose for which they are used
...

• Neutron energies:
(a) High energyas in fast reactors
(b) Intermediate energy
(c) Low energyas in thermal reactors
...
blogspot
...
PM5

50

...

bl

• Types of fuel:
(a) Natural uranium (238U = 99
...
714%)
(b) Enriched uranium (Higher % of 235U)
(c) Uranium 233 (obtained from 232Th)
(d) 234Pu (obtained from 238U)
• Types of fuel moderator assembly:
(a) Homogeneousin which fuel is dissolved in the moderator
...

• Moderators:
(a) Heavy water (D2O)
(b) Ordinary water (H2O)
(c) Graphite
(d) Beryllium
(e) Beryllium oxide
...

• Purposes:
(a) For research
(b) For production of 239Pu
(c) For power generation
...

(ii) Fast, enriched uranium, heterogeneous, liquid metal cooled, power breeder reactor
...
Reactor Core: Reactor cores are generally a right circular cylinder with dia
...
5 m to
15 m
...
The cylinder with the pressure vessel is
considered as reactor core
...
In the reactor core, the fission chain reaction takes place and the
energy is liberated in the form of heat
...
They are
usually clad in a thin sheath of Zr or Al stainless steel
...
For the passage of the coolants, enough space is provided between
the individual rods (Fig
...
5)
...
3
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH3-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

52

bl

2
...
It is used to reflect back some of the leaking neutrons from the reactor
core
...

3
...

rs

(ii) To keep power production steady
...

gi

ca

lu

ni

ve

The control system also plays an important role to control the chain reaction, so that
violent and damaging consequences may be avoided
...
The advantage is, they do not become radioactive
due to neutron capture
...
To shut
down a reactor the control rods are inserted to a considerable depth so that the chain reaction
ceases
...
Movement of control rods can be made mannual or automatic
...
Moderator: Function of moderator is to slow down the fast moving fission neutrons
...

(b) a low cross-section is used for better neutron absorption
...
The following are the drawbacks of D2O:
(i) Low boiling point,

te

(ii) necessitating the use of pressure
(iii) It is very expensive but its advantage outweighs its high cost
...
Reactor grade graphite is not good as a moderator but it is cheaper than Be
...
Coolants: Function of the coolants is to remove the heat produced in the reactors
...
They can act also as the moderator
...
They need pressurisation
...

• Molten metallic Na or K are excellent coolants
...
So it needs shielding
...
The only disadvantage is they are inferior to H2O
or liquid metals as coolants
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH3-1
...
c
ot
og

sp

53

NUCLEAR CHEMISTRY

bl

6
...
Its purpose is
to weaken the γ-rays and neutrons coming out of the reactors so that they cannot do any harm
to the persons in immediate vicinity
...

y
...

rs

it

(b) Biological Shield: It is a layer of concrete of few decimeter thick surrounding the
thermal shield
...

ve

Breeder Reactor

238U

captures 0
...
In general type of
reactors the conversion factor is 0
...
A reactor with the conversion factor above unity is known
as breeder reactor
...
In
this case, per nuclear fission, 2
...
5 neutrons escape out of
the reactor
...
The
residual 1
...
6 neutrons
...
9 neutrons and it is noteworthy to mention
is a manmade nuclear fuel
...
The application of isotopes depends on the fact that
the chemical properties of the isotope of a given element are essentially identical
...
The radioactivity or mass of an isotope can act as a tag or label which
permits the fate of the element or of a compound containing this element to be traced through
a series of chemical and physical changes
...
A few example of the use of radioactive tracers are given below:
(a) Photosynthesis in plants: When plants come in contact with sunlight, they can
take up CO2 and water, which are then converted into sugar and starches
...
The O2 produced may come from CO2 or H2O molecules or from both
...

6CO2* + 10H2O → C6H12O6* + 6H2O* + 6O2
6CO2 + 12H2O* → C6H12O6 + 6H2O + 6O2*
(b) Agriculture: During growth, plant absorbs elemental P both from the soil and from
the added fertilizer
...

(c) Medicine and diagnosis: (i) Radioisotopes are used to locate the presence of tumours,
particularly brain tumours
...

(iii) 131I is used to diagnose malfunctioning of liver, kidney, etc
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH3-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

54

it

y
...
The disappearance of radioactivity indicates that all the P have
been removed
...
The appearance of radioactivity in engine oil or in lubricants shows
that the process of wear and tear of the pistons has started
...

In ester hydrolysis, the acyl oxygen cleavage or alkyl oxygen cleavage can be determined as
follows:

O


CH3¾C¾O—C2H5 + H2O* → CH3 C OH + C2H5*OH (alkyl oxygen cleavage)

ni

ve

O

O


CH3¾C¾OC2H5 + H2O* → CH3 C *OH + C2H5OH (acyl oxygen cleavage)

ca

lu

O

gi

(f ) Biological research: Isotopic tracers have been widely used in cellular biology
...

lo

(g) Isotopic dating in Geology: The age of a rock or mineral containing uranium can
be determined by its radioactive decay
...

U238

still left
...

ht
tp
:/
/k
er
al
a

Since all U238 has been decayed to Pb206
...

A similar relation holds good for U235, so we have
U235 = (U235 + Pb207) e − λ ′ t

where λ′ = decay constant for U235
...
λ and λ′ can be determined from the half-lives of
two isotopes of U
...
blogspot
...
PM5

54

...

a
2
...

Alternatively, the age of a rock can be determined as follows
...

present in the rock at time t is:

a = U238 + Pb206 and (a x) = U238
represent their respective masses
...

(a x) = amount of U238 still left after the lapse of time (t)
...
303
Pb 206
log 1 + 238
t
U

lo

gi

F
GH

I
...
303
U 238 + Pb 206
log
t
U 238

ca

λ=

So,

0
...
303 t1/2
Pb 206
log 1 + 238
0
...

JK

(h) Radio-carbon dating technique: The age of a piece of wood or animal fossil can be
determined by radio-carbon dating technique
...

In radio-carbon dating ratio C14 to C12 is assumed constant in the plant; as the plant
assimilates CO2 with C14O2 during photosynthesis
...

Here, a =
(a x) =

C 14
C 12
C 14
C 12

t=

2
...

0
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH3-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

56

bl

So, by measuring the ratio C14 to C12 in the fresh and dead plants, age of the wood (t) can
be calculated
...

Example 1
...
D
...
D
...

Sol
...

n

ve

F 1I
Mass of radium left = M G J
H 2K
F 1I
= 200 G J
H 2K

rs

6480
=4
1620

No
...
5 mg
...
A radioactive source contains one microgram (µg) of Pu239
...
in all directions
...

= 4
...
m
...

gi

Sol
...
00387 × 1
...
646 × 1024 g

ch

no

Mass of 2300 α-particles

−

= 14
...
464 × 1024 g

Half-life (t1/2) of Pu239

=

− d M/ dt − 14
...
8672 × 1015 sec1
...
693
0
...

=
λ
14
...
478 × 106 years
...
Prove that N ≈ 0
...

N = N0eλt

Sol
...

1
λ

= N0e1 =

N0
e

N0
= 0
...
37 N0
...
718

Highlight:
• The radioactive constant (λ) may also be defined as the reciprocal of time during
which the number of a radioactive element falls to 37% of its original mass
...
blogspot
...
PM5

56

...
693
0
...
173
t1/2
2
...

M0 = Initial mass of 92U234
M = Mass at the end of 62,000 yrs
...
(a) Let,

bl

Example 4
...
0 mg of 92U234
...
48 × 105 yrs
...
88 × 1014 s1)
...
173
M = M0e0
...
189

M=

(b) Activity of

234

92U

left unchanged =

234

lo

92U

is:

4
= 3
...

1
...
e0
...
189 M

or,

lu

ni

λt may also be calculated, as follows:
λt = 8
...
88 × 1014 ×

3
...
023 × 10 23
234

te

= 7
...

ht
tp
:/
/k
er
al
a

Example 5
...
In how many years will one
gram of pure element (a) lose one centigram (b) be reduced to one centigram?
Sol
...
693 0
...
28 × 104 year1
...

The mass of radium would be left behind at the end of time t = 1 0
...
99 g
...
4343
N
100
= 4
...
4343
99
t = 23
...

N0
1
=
= 100
N
0
...
blogspot
...
PM5

57

...
28 × 104t × 0
...

bl

∴

ve

dN
= λN
dt

3
...
31 × 104 ×

m × 6
...
02 × 10 23
214

ni

−

Now,

it

y
...
The unit for measuring radioactivity is curie (Ci)
...
7 × 1010 disintegrations/sec
...
7 × 1010 dis/s
...
The number of atoms of RaB contained in mass (m)
=

m = 3
...

ca

∴
Highlights:

lo

gi

• A new absolute unit of radioactivity is rutherford (rd)
...
s1
...

no

Example 7
...

ht
tp
:/
/k
er
al
a

∴

te

∴

ch

Sol
...
s −1
dt

106 = 4
...
3 × 1013 g
...
5 × 109 years) is:

238
92 U

m × 6
...
693/4
...
7 × 1010 = 4
...
023 × 10 23
238

m = 3
...

∴

• For one rutherford, the mass of

92U

238

is

106 = 4
...
023 × 10 23
238

m = 80
...

Example 8
...
5
...
(t1/2 for U
is 4
...
We know that,
U238 = (U238 + Pb206) eλt

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH3-1
...
c
ot
og

Pb 206
U 238

I
JK e

λt

bl

F
GH

1 = 1+

or,

0
...
303 × log10 1
...
3 × 0
...
23 × 0
...
5 × 10 9

ve

or,

it

∴

y
...
5) eλt = 1
...
5

or,

t = 2
...

∴

11
...
05
238

Mole of Pb206 =

10
...
05
206

gi

F
GH

2
...
693
U

lo

t=

ch

no

We have,

ca

Mole of U238 =

lu

ni

Example 9
...
9 g of U238 and 10
...

Calculate the age of the ore
...
5 × 109 years)
Sol
...
303 × 4
...
05
log 1 +
=
0
...
05

IJ
K

te

2
...
5 × 10 9
log 2 = 4
...

0
...
The amount of 6C14 isotope in a piece of fresh wood is found to be 1/6th of
the total carbon
...
(t1/2 of C = 5577 yrs)
...
We have,

ht
tp
:/
/k
er
al
a

=

t=

2
...
693
1/ 6

2
...
693
2
...
7782
=
= 20,170 yrs
...
693
Example 11
...
An old piece of wood in a museum has
a disintegration rate which is 25% of the disintegration rate of an equal weight of a new piece of
wood
...
We have,
=

t=
=

2
...
693
1/ 4
2
...
6021
= 11,525 yrs
...
693

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH3-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

60

bl

Example 12
...
13 hrs
...

2
...
13
log x
0
...
693
= 0
...
303 × 6
...
303 t1/2
1
log
0
...

Sol
...
4696 = 2
...

3

ca

∴ the fraction of the Sample =

lu

x≈3

gi

Example 13
...

no

14
7N

ht
tp
:/
/k
er
al
a

te

ch

Sol
...
This energy which is generally abbreviated by Q is also known as energy
balance of the reaction as per Einsteins theory or more commonly as Q-value
...
On the other hand, if Q-value is negative,
there is absorption of energy, there is gain of mass in the reaction, and such reaction are called
endothermic or endoergic
...
m
...
)

Product particles

Mass (a
...
u
...
00387

17
8O

17
...
00753

1
1H

1
...
01140

Total = 18
...
01264 18
...
00124 a
...
u
...
00124 × 931 MeV

[Q 1 a
...
u
...
15 MeV
So, the reaction is

2He

4

+ 7N14 = 8O17 + 1H1 + Q

∴ Q-value of the reaction is = 0
...
m
...
= 1
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH3-2
...
c
ot
og

Example 14
...

bl

3 Li

Mass (a
...
u
...
01822

2He

+ 1H1 = 2He4 + 2He4 + Q
Q = Decrease in mass

3Li

4
...
00774

ni

7

∴
∴

4
...
02636

rs

4

4
2He

Mass (a
...
u
...

Sol
...
00814

lu

= (8
...
00774) = 0
...
m
...

= 0
...
3 MeV
...

So the reaction is exothermic of exoergic
...
Calculate the energy released from the fusion of 3 Li6 and 1D2 by the reaction,
6

no

lo

+ 1D2 = 2 He4 + 2 He4 + Q
where isotopic masses are, 3 Li6 = 6
...
m
...

3 Li

4
= 2
...
00387 a
...
u
...
From the above equation,
Q = (2
...
01702) (2 × 4
...
03402 a
...
u
...
03402 × 931 = 31
...

Example 16
...

Sol
...
124 + 1
...
945 + 138
...
0099)
= 0
...
m
...

∴ Energy released

= 0
...
258 MeV
...
Calculate the limiting energy per nucleon 20Ca40, which has atomic mass
of 39
...
m
...
The mass of proton is 1
...
m
...
and the mass of neutron is 1
...
m
...

Sol
...
0078 + 20 × 1
...
975 a
...
u
...
353 a
...
u
...
353 × 931
MeV
...
216 MeV
...
Calculate (i) the fission rate of U 235 for producing power of 1 watt and
(ii) the energy released in the complete fission of 1 kg of U 235
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH3-2
...
c
ot
og

ENGINEERING CHEMISTRY

y
...
1 × 1010 fissions sec1
...
2 × 10 −11

bl

Sol
...
6 × 1013 J = 3
...
s
...
2 × 1013 J
...
023 × 10 26
MeV
...
023 × 1026 atoms or nuclides
...
6 × 1013 J)

gi

ca

Example 19
...
If this is to be
supplied by a nuclear reactor of efficiency 20%, using U 235 as the nuclear fuel, calculate the
amount of fuel required for one days operation
...

lo

Sol
...
2
Energy released/nuclide = 200 × 1
...

∴ No
...
5 × 1023
32 × 10 −12

6
...
5 × 1023 atoms of U235 are present in

235 × 13
...
025 × 10 26
= 530 × 103 kg = 0
...

SHORT QUESTIONS AND ANSWERS
Q
...
What do you mean by nuclear chemistry?
Ans
...
e
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH3-2
...
c
ot
og
bl

Q
...
How does a nuclear reaction differ from a chemical reaction?

y
...
Nuclear reaction involves the changes of the nucleus whereas ordinary chemical
reaction involves the changes in extranuclear electrons of the atoms, nuclei of the atoms remain
unaffected in a chemical reaction
...
3
...
The phenomenon of spontaneous emission of radiations from the nuclei of heavy
elements is called radioactivity
...

ve

Q
...
What is the theory behind radioactivity emission?
Ans
...

ca

(iii) α- and β-particles are emitted from the nucleus
...

Q
...
What is α-emmision?

−α
→ 2He4 + 90UXI234
...
The emission of an α-particle from a radioactive nucleus is designated as α-emission
...
6
...
The emission of a β-particle from a radioactive element is known as β-emission
...
So it appears strange
...
Thus, the
atomic number of the daughter element increases by one unit
...
7
...
γ-rays have been proved to arise from the transition of a nucleon from one energy
state to the other
...

RaD

210
82Pb

E = 65 KeV
b-ray

210

83Bi

E = 47 KeV

g-ray

RaE

210
83Bi

E=0

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH3-2
...
c
ot
og

ENGINEERING CHEMISTRY

sp

64

Q
...
What do you mean by natural radioactivity and artificial radioactivity?

it

y
...
Natural radioactivity is exhibited by heavier elements found in nature
...
Such type of radioactivity is known as artificial
or induced radioactivity
...
9
...
If, during radioactive disintegration, the daughter element is also radioactive then
it decays further and the process continues till a stable isotope is reached
...

Q
...
What do you mean by radioactive decay constant?

dN
= λN
dt

lu

−

ni

Ans
...

Alternatively, it may be defined as the rate of disintegration when the number of
radioactive nucleus present is one
...
11
...

Ans
...

(ii) Radioactive change is irreversible
...

(ii) Chemical change is mostly reversible
...

(iii) Chemical change may be exothermic or
endothermic
...

(iv) Chemical change involves only outermost
electrons of the atoms
...

Q
...
What do you mean by nuclear fission?
Ans
...
As for example:

92U

56Ba
235

1

+ 0n ¾¾®

92U

236

54Xe
55Cs

140

144

144

+ 36Kr

93

90

+ 38Sr

+ 37Rb

90

+ 3 0n
+ 2 0n

1

1

+ 2 0n

1

A huge amount of energy is released during nuclear fission according to famous Einsteins
equation E = mc2, and this reaction is the principle for atom bomb
...
blogspot
...
PM5

64

...
13
...
When two light nuclei combine with release of a huge amount of energy, the
phenomenon is known as nuclear fusion
...

2
1H
1
1H

it

+ 1H3 → 2He4 + energy
...

rs

Nuclear fusion is the source of energy of the sun and the other stars
...
In the sun, at a temperature of ten
million degrees; the following fusion takes place
...
14
...
The pressure and temperature at the centre of very large stars is high enough for
nuclei to fuse to form heavier elements such as C, Si, Fe, since 2He4 has even number of
nucleons, they fuse to produce elements with even proton numbers
...
15
...

lo

Ans
...
Nuclear reactions
are brought about by bombarding nuclei with high energy particles in particle accelerators or
with beams of neutrons from nuclear reactors
...

+ 0n1 → 92U239 β → 93Np239 β → 94Pu239


Nuclear reactions are used to give birth to radioactive isotopes to be used as tracers
...
16
...

Ans
...

(i) Fusion involves, combining of two lighter
nuclei into a heavy nucleus with release of
large amount of energy
...

(ii) Fusion takes place at very high temperature
(106 K)
...

(iv) Fission gives rise to chain reaction
...

(v) Fusion does not give rise to chain reaction
...

What is radioactivity? Give an account of the discovery of radioactivity?

2
...

If you are given a piece of mineral, how can you determine by simple experiments if the mineral
is radioactive?

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH3-2
...
c
ot
sp
og
bl
y
...
blogspot
...
etc to
eduktu@gmail
...
blogspot
...
c
ot
og

ENGINEERING CHEMISTRY

sp

66

What are α-, β- and γ-rays? Compare their ionising power, range and velocity
...
What are the units of radioactivity?
7
...

8
...

9
...
What do you mean by the half-life period
of a radioactive element? Show that the half-life is independent of the amount of the substance
...
Explain artificial radioactivity with suitable examples
...
What is radioactive displacement law?
12
...

13
...
What is a nuclear reaction? Discuss some uses of nuclear reactions
...
What is nuclear binding energy?
16
...

17
...

What informations are available from these curves?
18
...

19
...

20
...

21
...
Derive a relation between mass defect and nuclear
binding energy
...
Where is the radioactive displacement law invalid?
23
...

92
0
24
...

25
...

bl

4
...

9
4 Be

+ 4 He →
2
24
11 Na
238
92 U

10
5B

12
6C

+
...

→

239
90Th

+
...
+ 1H
2
1

7
3 Li

+ 1H →
...

1
4

26
...
Given the t1/2 of
thorium = 1
...

[Ans
...
93 × 105 yrs
...
Calculate the binding energy in MeV per nucleon of

12
...
00782 a
...
u
...
00866 a
...
u
...
04
1 amu = 931
...

[Ans
...
76 MeV]
28
...
How long will it take for 1 g of the element to lose 0
...
2385 yrs
...
blogspot
...
PM5

66

...

bl

29
...
7 times that in a living plant
...
Given t1/2 = 5760 years
...
2970 years]
30
...
9 g of 238U and 10
...
of 206Pb
...
Given t1/2 of uranium = 4
...

[Ans
...
5 × 109 years]
31
...
82 days
...

[Ans
...
5 × 106]
32
...
What is its halflife period?
[Ans
...
Calculate the energy released in MeV from the reaction:
+ 1H
1

1
+ 3 H → 4 He + 0 n
1
2

no

2
1H

lo

gi

ca

lu

ni

ve

Given: Mass of 10B = 10
...
m
...

Mass of 11B = 11
...
m
...

Mass of 2H = 2
...
m
...

Mass of 1H = 1
...
m
...

[Ans
...
114 MeV]
34
...
Calculate the energy produced in MeV
...
6747 × 1024 g
...
6725 × 1024 g
...

1 a
...
u
...

[Ans
...
73 MeV]
35
...
Given the t1/2 of cobalt = 5
...

[Ans
...
13 yr1]
36
...
014 a
...
u
...
016 a
...
u
...
003 a
...
u
...
009 a
...
u
...
16
...

A fresh sample of wood shows 15
...
An old wooden article shows 2
...
Calculate the age of the wooden article
...

[Ans
...
Distinguish between nuclear fuel and a chemical fuel
...
Write short note on components of a nuclear power reactor and their functions
...
blogspot
...
PM5

67

...

it

4

ve

rs

Thermodynamics

lo

gi

ca

lu

ni

Thermodynamics is concerned with the flow of heat and therefore deals with the quantitative
relationship between heat and work
...
Thermodynamic deductions are not made
on the basis of any hypothesis about the molecular structure of matter but the three simple
laws of thermodynamics are based on human experience and these relations were tested
experimentally for centuries starting from heat engines to cellular enzymatic processes and
are considered inviolable
...

ch

no

Before beginning with the laws of thermodynamics following terms are needed to be
defined
...
Thermodynamic systems
...
The rest of
the universe is called the surroundings
...
Hence, the energy and matter remain constant for the
system
...

A closed system is one, which is capable of exchanging only energy with the surroundings
but no mass transfer across the boundary is permitted; example is a sealed flask containing
matter in a closed system
...

2
...
The physical characteristics which are experimentally
measurable and which enable us to define a system are called thermodynamic parameters or
properties of the system
...
Refractive index, viscosity, dielectric constant are also other properties
...
Properties like volume, surface area, energy, etc
...

Intensive property
...
, are independent of the mass of the system and are
called intensive properties
...
State of a system
...
, which describe a system is called the state of the system
...

68
http://keralatechnologicaluniversity
...
com

...

y
...

rs

it

If a change takes place in a thermally insulated system which does not permit heat
exchange with the surrounding, the process is called an adiabatic process and the temperature
of the system may increase or decrease
...

ca

lu

ni

If a change takes place in which the volume of the system remains constant the process
is called an isochoric process
...
A process can be made reversible by performing the change very slowly
with no friction and no finite temperature differences
...
All the natural processes are irreversible, example,
expansion of gases from high pressure to low pressure, heat flowing from a hotter to a colder
body, etc
...

te

ch

Equilibrium state
...
Hence, a system in equilibrium
state has definite temperature, pressure and composition
...
Internal energy change (∆E), enthalpy
change (∆H), free energy change (∆G) and entropy change (∆S) are such functions
...
Every system within itself has a quantity of energy which is called the
internal or intrinsic energy
...
The magnitude of internal energy of a system is determined
by the kinetic, rotational, vibrational movements of the molecules of the system
...
Five moles of a substance in a specified state has five times the internal energy
possessed by a single molecule in a similar state
...
When a system changes from a thermodynamic state 1 to a
thermodynamic state 2, the change in the internal energy ∆E = E2 E1 is independent of the
path of transformation but depends on the initial and final conditions of the system
...
e
...
e
...
So internal energy (E) is a state
function
...
4
...
e
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH4-1
...
c
ot
y
...
4
...

The law was first stated by Mayer in 1842 and Foulis classical research on equivalence
between heat and work established the fact in 1845 and finally generalised by Helmholtz
in 1847
...
Since heat energy cannot be lost, it may
be used up by the system as partly increasing the internal energy of the system and partly in
doing mechanical work
...
e
...
For an adiabatic change, q = 0, ∴ W = ∆E
...
If the system is under a pressure P and volume increases by dV, the work done becomes
P dV and hence the mathematical expression of first law becomes, dE = dq P
...

Here the work, exclusively, is of pressure × volume type
...
e
...

Hence, from first law,
∆E = q W = 0
∴
q = W
...

Joule-Thomson effect
Joule-Thomson effect states: When a gas under high pressure is permitted to expand
into a region of low pressure, it suffers a fall in temperature
...
blogspot
...
PM5

70

...

bl

Joule and Thomson performed an experiment where a gas was allowed to expand
adiabatically through a porous plug against a constant pressure
...

Suppose V1 volume of gas at pressure P1 is forced through the porous plug and expands
to a volume V2 at a lower pressure P2
...

For an ideal gas,
P1V1 = P2V2 ∴ W = 0
...

Hence, for an ideal gas, there should be no change in temperature
...
Since the expansion is carried
out adiabatically i
...
, when q = 0, the energy of the gas falls i
...
, ∆E = ve; thus the gas while
expanding does some work and hence the temperature falls
...

ht
tp
:/
/k
er
al
a

te

ch

no

lo

gi

The pressure (P) and volume (V) of a system are thermodynamic variables and their
product PV is expressed as energy
...
The volume increase is from V1 to V2
...
Hence, from the first law of thermodynamics
q = (E2 E1) + W
= (E2 E1) + (P2V2 P1V1)
= (E2 + P2V2) (E1 + P1V1)
= H2 H1 = ∆H
...
Since E is a characteristic of the system (state function), according to the
first law, H is a similar state function
...

∆H = (E2 + P2V2) (E1 + P1V1)
= (E2 E1) + (P2V2 P1V1)
∴ At constant pressure,
∆H = ∆E + PV = ∆E + W = q (heat absorbed)
and at constant volume,
∆V = 0
...

i
...
,
Change in enthalpy = change in internal energy
...

Constancy of Enthalpy (isoenthalpic) in Joule-Thomson expansion

Joule-Thomson experiment is carried out adiabatically, when heat does not flow out of
the system nor does it come into system from the surrounding, i
...
, q = 0
...
4
...

Porous plug
V1

P1

P2

V2

Fig
...
2 Joule-Thomson expansion
...
blogspot
...
PM5

71

...
e
...

∆H = ∆E + P∆V = ∆E + P(V2 V1)
= ∆E + w = qP (heat absorbed at constant pressure)
i
...
, change in enthalpy is equal to heat absorbed at constant pressure
...

bl

Hence, from first law,

og

ENGINEERING CHEMISTRY

H

lu

FG δT IJ
H δP K

ni

ve

Inversion temperature
If the gas in above expansion suffers a fall in temperature by dT, for a lowering of
pressure dP, we can define Joule-Thomson coefficient (µ) by the relation,
µ=

ht
tp
:/
/k
er
al
a

te

ch

no

lo

gi

ca

µ is zero for an ideal gas (PV = nRT)
...
under adiabatic conditions
...
e
...

The cooling effect is seen when the temperature is low
...
e
...
For every gas there is a
temperature where µ = 0, when neither heating nor cooling of the gases occurs on expansion
after pasing through orifices
...

Work done in a reversible isothermal expansion: Suppose n moles of a gas is
enclosed in a cylinder by a frictionless piston (Fig
...
3)
...
e
...
i
...
, isothermal
condition is maintained
...
The gas is to be
expanded from volume V1 to volume V2
...

W = force × displacement
= force × area × distance
A
= P × a × l
...

a × ∆l is the volume swept by the piston, it is dV
Fig
...
3

z

V2

PdV =

Then,

W=

∴

V2
W = nRT ln V
1

Since,

V1

z

V2

V1

nRT
dV
V

[Q PV = nRT]

P
V2
= 2 in an isothermal expansion of a perfect gas
...
blogspot
...
PM5

72

sp

72

...

W = RT ln

bl

W = nRT ln

V2

...

or

P∆V = ∆n
...

ni

P(V2 V1) = (n2 n1) RT
...

∴

lu

From first law of thermodynamics, ∆H = ∆E + P∆V
...
RT
...

gi

When the reaction involves gaseous expansion,
∆n is positive,

When the reaction involves gaseous contraction,
∴ ∆H < ∆E
...

Heat capacity

te

ch

Heat capacity (C) of a substance is the amount of heat needed to raise the temperature
of 1 gm of the substance by 1°C
...

ht
tp
:/
/k
er
al
a

Molar heat capacity at constant volume is Cv, which is molar heat capacity measured at
constant volume condition
...

Molar heat capacity at constant pressure is measured by keeping the pressure constant
∴

Cp =

FG IJ
H K

∂H
dq
=
∂T
dT

P

...
blogspot
...
PM5

73

sp

73

THERMODYNAMICS

...

it
rs
ve
ni
lu
ca
gi
lo
no
ch
te
ht
tp
:/
/k
er
al
a
http://keralatechnologicaluniversity
...
com

...

bl

the disorder and irreversibility and when equilibrium is reached, it has the maximum disorder
...

For example, if a gas with strong odour is let loose at the corner of a room, the odour of the gas
spreads all over the room randomly and equilibrium is reached when the entropy also becomes
maximum
...

• A spontaneous change occurs in the direction leading to a total increase of entropy
...
(i) the entropy
change of the system and the entropy change of the surroundings i
...
,
∆Stotal = ∆Ssystem + ∆Ssurroundings
...

• Entropy is a state function dependent on P, V, T and path independent
...

• Any irreversible process is accompanied by increase in entropy
...

ch

no

lo

• Entropy is a measurement of randomness of a system
...

So, increase of randomness enhances thermodynamic probability
...

te

As w is always greater than one, w increases when S increases
...

For example, solidification of a liquid brings about orderly state and thereby entropy decreases
...
e
...
The energy unavailable as work is proportional to the
increase of entropy
...
Thus, entropy
signifies unavailable form of energy of the system during transformation of heat into work
...
4
...
The volume of the
gas changes from V1 to V2
...

Hence, from 1st law of thermodynamics,
dq = dE + dW = dE + P dV
...

dT
dV
+R

...
blogspot
...
PM5

75

...
c
ot
og

ENGINEERING CHEMISTRY

Thus, for a change from states 1 to 2 we have,

∆S = Cv ln

z

V2

V1

dV
V

bl

T1

dT
+R
T

y
...

T1
V1

Since, for an ideal gas at constant temperature,

P
V2
= 1
P2
V1

ve

P1
T2
+ R ln

...
e
...

P2
V1

∆S = Cv ln

lu

ni

∴

it

S1

dS = Cv

rs

z

S2

gi

T2
∆Sp = Cp ln T
1

lo

At constant volume V,

ca

At constant pressure P,

no

∆Sv = Cv ln

T2

...
The change of entropy of a given system from state 1 to state 2
is always the same and is path independent if the path is reversible
...

T
When the flow of heat is irreversible, let a heat reservoir at T1 (state 1) is brought in
contact with a second reservoir at T2 (state 2) where T1 > T2, and small quantity of heat q flows
from T1 to T2
...
1
∴ Net change of entropy =
T2 T1
T1T2
The difference is a positive quantity, hence, the irreversible heat flow leads to increase
in entropy
...
The vessel is connected
to a vessel of volume V2 by a tube containing stop cock, which is evacuated (Fig
...
4)
...
From the first law of thermodynamics,
we have,
q = ∆E + W

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH4-1
...
c
ot
og

sp

77

THERMODYNAMICS

V1

V2

it

V1 + V2
V1
...

qrev = ∆E + RT ln

bl

Now, if this expansion is carried out irreversibly at T K from volume V1 to a volume
(V1 + V2) after opening the stop cock (Fig
...
4)
...
4
...
(system) would be same
...

V1

lo

gi

ca

= R ln

no

Entropy change of a mixture of gases
From first law of themodynamics, we have,

te

ch

dq = dE + PdV
Dividing both the sides of the above equation by T,

ht
tp
:/
/k
er
al
a

or,

or,
where S0 is a constant
...

RT
+ S0
P
or,
S = Cp ln T R ln P + S0′
We cannot determine the absolute value of the entropy of an ideal gas
...
Thus, if the temperature of an ideal gas changes from T1 to T2
and the volume from V1 to V2 for 1 mol
...

V1
P2

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH4-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

78

bl

When two gases come in contact, they diffuse and mix-up irreversibly
...

y
...

The entropies of the two gases in the mixture are

ca

SA(mix) = nA[C PA ln T − R ln pA + S A 0 ]

gi

SB(mix) = nB[C PB ln T − R ln pB + S B 0 ]
So, change of entropy due to mixing,

lo

∆Smix = (S A mix + S Bmix ) (SA + SB)

no

= S A mix + S Bmix SA SB

∆S = nA R ln

ch

or,

pA
p
nB R ln B
P
P

ht
tp
:/
/k
er
al
a

te

The total moles of mixture = n = nA + nB mol
...
fraction = pressure fraction)
P
P
∆S = nA R ln xA nB R ln xB
...
fraction of gas i
...
So, work function is such a
thermodynamic property of the system that decreases in work function A i
...
, ( ∆A) gives the
maximum amount of work available during isothermal process
...
blogspot
...
PM5

78

...

it

Free energy (G)

FG δA IJ
H δV K

y
...

rs

Two thermodynamic functions, which are very useful for physicochemical studies are:
• Gibbs free energy (G) and • Helmholtz free energy or work function (A)
...

∆G = ∆H T∆S
...

lu

Free energy and useful work

gi

ca

Suppose a reversible change takes place at constant temperature T and at constant
pressure P
...
Therefore, from the first law of
thermodynamics, we have,

lo

q = ∆E + P∆V + Wuseful
= ∆H + Wuseful
q = T∆S,

no

Now, since

ch

T∆S = ∆H + Wuseful

∆H T∆S = Wuseful

te

∴

ht
tp
:/
/k
er
al
a

or,

= (∆G)P, T
...

Hence, decrease in Gibbs free energy is a measure of the useful work obtainable from
the process
...
To assign numerical values to free energy change of a system, it is
necessary to assign a standard value for the free energy of a system at a specified state
...
e
...

Therefore, standard free energy change (∆G°) is defined as the free energy change for a
process taking place at standard state for the reactants and the products obtained are also in
their standard states
...

= nFE (n = number of electrons, F = Faraday and E = emf of a cell
...
blogspot
...
PM5

79

sp

79

THERMODYNAMICS

...

bl

(iii) ∆G° = RT ln K
= 2
...

where R = gas constant, T = temperature in kelvin, K is the equilibrium constant of a
reaction
...

At constant temperature and pressure always system tends to attain a position of
minimum free energy which is the position of equilibrium
...
If ∆G is negative, any change
shall spontaneously occur
...

ca

lu

Highlights:
• First law of thermodynamics statesthe energy may change from one form to
another, but the sum total of energy of the universe remains constant
...

• Entropy is a measure of randomness or disorder of a system
...

T
• State function is one which depends only on the initial and final states of the
system but independent of the path followed e
...
, ∆G, ∆S, etc
...

ht
tp
:/
/k
er
al
a

te

unavailable energy
...
The reactions in which heat
is evolved are termed exothermic and in which heat is absorbed are endothermic
...
The
thermal changes in chemical processes are governed by two general principles, both of which
are corollaries of the first law
...
Law of Lavoisier and Laplace
...

1
1
H (g) +
Cl2(g) → HCl(g)
∆H = 92 kJ
2 2
2
1
1
HCl(g) →
H2(g) +
Cl2 (g)
∆H = + 92 kJ
2
2
According to the first law, heat content (H) or energy content (E) of the initial reactants
again returns to the same magnitude
...
blogspot
...
PM5

80

...

bl

change is zero i
...
, heat changes in the two directions must be equal in magnitude but opposite
in sign
...
Hesss Law of Constant Heat Summation
...
Let us take the example of formation of CO2 in one step and two steps (a)
and (b):
C + O2 = CO2
∆H = 94
...
42 Kcal
2
1
(b)
CO +
O = CO2
∆H2 = 67
...

2 2
Summing up we get, ∆H1 + ∆H2 = ( 26
...
63) Kcal
which illustrates the law
= 94
...

From first law we find that ∆HP and ∆EV will be independent of the path
...
, which are difficult

no

lo

gi

Highlights:
Hesss law is used to calculate:
• Enthalpy changes (∆H) of formation from enthalpy changes of combustion
...

• Lattice energies is the Born-Haber cycle
...
e
...

(i) Heat of reaction
...

Example:
(a) H2 + Cl2 = 2 HCl
+43,608 cals (exothermic)
(b)
H2 + I2 = 2 HI
12,680 cals (endothermic)
Thus, the heat of reaction for the formation of 2 moles of HCl
is 43,600 cal which is exothermic whereas for the formation of 2
moles of HI, 12,680 cal of heat is absorbed and the reaction is
endothermic
...
Heat change for the complete
combustion of a gm-mole of the substance at a given temperature
under normal pressure is called its heat of combustion
...

In the case of organic compounds, complete combustion means
when these compounds are converted finally to CO2 and H2O
...
4
...

bomb calorimeter which is a pressure vessel internally enamelled
with platinum (Fig
...
5)
...

Example:
C2H5OH + 3O2 = 2CO2 + 3H2O
∆H = 325 Kcal

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH4-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

82

ht
tp
:/
/k
er
al
a

te

ch

no

lo

gi

ca

lu

ni

ve

rs

it

y
...

Example:
HNO3(aq) + NaOH(aq) → NaNO3(aq) + H2O
∆H = 13
...
7 Kcal
...
e
...
e
...

Therefore, the heat of neutralisation is really the heat of formation of 1 gm mole of
water from 1 gm ion of hydrogen and hydroxyl ion, and this is always the equivalent of 13
...

But when a weak acid or a weak base is neutralized, the heat of neutralisation deviates
considerably from 13
...

(iv) Heat of formation
...
The standard enthalpy of formation (∆Hfo) is just the negative
of the heat of formation
...
Conventionally, the enthalpy of any element at 1 atm and
298 K is assumed to be zero
...
8 kJ
...
The lower the enthalpy
of formation of a compound, the more stable is the compound
...
Whereas, when the
enthalpy of formation of a compound is negative, the energy content of the corresponding
compound is lower than its constituent elements and hence the compound is stable
...

Example:
∆Hf of HI is + 26
...
7 kJ indicates the HF is much more stable
than HI
...
The heat change taking place when 1 gm mole
of the solute is completely dissolved in a solvent is called the heat of solution
...
e
...

The value of heat of solution obtained graphically by extrapolating ∆H to infinite dilution
is the integral heat of solution at infinite dilution
...

Example:
KCl(s) + 50 H2O = KCl (50 H2O)
4276 Cal
...

(vi) Heat of fusion
...

Heat of fusion is always positive
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH4-1
...
c
ot
og

sp

83

THERMODYNAMICS

rs

it

y
...
It is the heat change involved in converting 1 mole of substance
from liquid to the gaseous state at its boiling point
...

Example:
H2O(l) → H2O(g)
∆H = 42 kJ
...
It is the heat change involved in converting 1 mole of solid
directly to its vapour at a temperature below the melting point of the substance
...
4 kJ
...

• The enthalpy change (∆H) is calculated when starting temperature of the reactants
and final temperature of the products are the same
...

• If ∆H is negative, the reaction is exothermic i
...
, the system loses energy to
surroundings
...
e
...

• The standard conditions for change of enthalpy (∆H) are 298 K and 1 bar (100
kPa), the standard enthalpy change is represented by ∆H°298
...
Many values are determined indirectly
using Hesss law
...

• Enthalpy change for melting, sublimation, vaporisation are measured at m
...
or
b
...

Bond Energy

Bond energy is defined as the average energy required to break the bonds present in a
molecule of gaseous compound, to atoms or radicals in gaseous form
...
This energy is dependent on the nature of the atoms present
as well as the environment
...
For water the energy of separating a H-atom is 118 Kcal, whereas this energy
of separating the second H-atom from the residual OH group is 102 Kcal
...

Taking average of the two bond energies we have
118 + 102
= 110 Kcal for OH bonds
...
e
...

4
Alternatively, we can also take the average of the four different dissociation energies of
CH bond of methane
...
blogspot
...
PM5

83

...

bl

(i) Bond energy varies with the size of the atoms
...
5 and 43
...

it

(ii) Bond energy varies with the difference between the electronegativity of the two atoms
...

(iii) Bond energy varies with the total environment of the molecule
...
So, the total enthalpy change involved
in these bond breaking and making gives the heat of reaction
...
e
...

lo

2C(g) + 6H(g) →

H H
 
H C C H(g)
 
H H

no

∆Hf for ethane is = 1 × (bond energy for CC) + 6 × (bond energy for CH)

te

ch

= (1 × 79
...
5) Kcal
...
3 Kcal mol1
...

Second law of thermodynamics guides the conditions under which heat and work are
interconvertible
...

1
...

2
...

From the above experience, second law of thermodynamics can be stated in some different
important forms,
(a) It is impossible to convert heat completely into an equivalent amount of work, without producing some other effects in the system
...

(c) All spontaneous processes tend to equilibrium
...

Effect of temperature on free energy-(Gibbs-Helmholtz equation)
We know,

H = E + PV and G = H TS
= E + PV TS

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH4-2
...
c
ot
We know,
∴

og

dG = dE + PdV + VdP TdS SdT
dq = dE + PdV
dG = dq + VdP TdS SdT

y
...

p

P

lu

F ∂∆G IJ
G ∂T K
H

∴

FG ∂G IJ
H ∂T K

∴

rs

∴

it

Again for reversible mechanical process dS =

bl

Differentiating, we get

∆G = ∆H T∆S

∴

∆G = ∆H T

gi

ca

∴

FG ∂∆G IJ
H ∂T K

p

no

lo

This is Gibbs-Helmholtz equation, which relates free energy and ethalpy changes at
constant pressure
...

We know that if ∆G is negative the reaction takes place spontaneously and when ∆G = 0
i
...
, when the free energy of the reactants and the products are equal, the reaction attains
equilibrium
...
e
...

(b) In endothermic process, ∆H is positive, the reaction occurs if T∆S is positive and
greater than ∆H
...

Hence, the criteria for spontaneous processes are:

(a) If ∆H is negative and ∆S is positive ∆G becomes negative
...

(c) If both ∆H and ∆S are positive and T∆S > ∆H
...
e
...
(ClapeyronClausius equation)
Change of phase taking place during freezing, vaporization, etc
...

Let G1 and G2 be the free energies of a liquid and its vapour, which are in equilibrium at
a temperature T
...
blogspot
...
PM5

85

sp

85

THERMODYNAMICS

...

y
...
The drop in free energy of the liquid is ∆G1 and corresponding gain in free energy
of the vapour is +∆G2
...
This equation is the famous Clapeyron-Clausius equation
...

1
...

gi

Application of Clapeyron-Clausius equation

lo

q
dP
=

...
V1) and vapor (Vol
...

L
q
dP
=
=
T V2
T V2
dT

PV = RT, i
...
, V =

∴

or,

RT
P

LP
dP
=
RT 2
dT

ht
tp
:/
/k
er
al
a

Now, for ideal gas

(q = L = latent heat of vaporization)

dT
dP
=L
...
303R T1 T2

OP
Q

P2
T2 − T1
L
log P =

...
303R T1T2
1

Thus, from the vapour pressures P1 and P2 at different temperatures T1 and T2 we can
determine the molar heat of vaporization with the integrated Clapeyron-Clausius equation
...
Effect of pressure on boiling point
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH4-2
...
c
ot
og

sp

87

THERMODYNAMICS

y
...
Effect of temperature on vapour pressure of a liquid: Again from the similar expression
we can calculate the vapour pressure of a liquid at a different temperature if the vapour of it is
known at a particular temperature alongwith its latent heat
...

At absolute zero temperature, kinetic energy of a substance is zero and it is present in a
perfectly arranged crystalline state
...

• Entropy and the third lawThird law can be used to determine the entropy of a
substance
...
These Cp values are plotted against T and can be
extrapolated to T = 0
...

Mathematically, we have

Cp
T

0

dT

z

S0 = 0
...
303 C p d log T

(I)

(II)

Cp

Cp
T
1
log T

2

O

10
T

20

30

Fig
...
6 Graphical determination of entropy
...

Many reactions occur in nature which have ∆G = positive only when they are coupled with
another reaction whose ∆G is much larger negative
...

Example
...
ATP is a high energy molecule, so when in the

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH4-2
...
c
ot
og

ENGINEERING CHEMISTRY

sp

88

y
...
Thus,
the energy of glucose oxidation can be utilised to carry out other non-spontaneous reaction via
ATP
...
g
...

• Hesss law states: For a chemical process, the amount of heat evolved or absorbed
is the same whether the process takes place in one step or in several steps
...

• ∆G is negative for a spontaneous reaction
...

• ∆G is positive for non-spontaneous reaction
...

• The entropy of the universe is increasing
...

• Clapeyron-Clausius equation is:

te

ch

q
dP
=

...

• A spontaneous process always has a net increase in entropy for the computation of the
change of entropy, the changes in entropy of both the system and the surrounding are
to be considered when a system is in equilibrium,
dStotal = 0
For any spontaneous irreversible process,
dStotal > 0

When a reversible process is at equilibrium,
dS + dS′ = 0
For a spontaneous process,
dS + dS′ > 0

where dS and dS′ are the changes of entropy of the system and the surroundings
respectively
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH4-2
...
c
ot
og

Chemical Potential (µ)

bl

Free energy per mole at a given temperature T and pressure (P) is called the chemical

y
...

G
(for a pure substance)
...

rs

FG ∂G IJ
H ∂n K

T, P , n j

ni

where nj represents the constant composition of a mixture
...

Just like temperature, pressure or electric potential it tends to equalise within all parts
of a system
...

lo

gi

Thus, chemical potential of water in ice must be same in both the phases
...
For the equilibrium,

Ice
(I)

Water
(II)

ch

no

If dn moles are transferred from phase I to phase II,
But for equilibrium,

dG = µ(II) dn µ(I) dn
dG = 0,
∴ µ(I) = µ(II)

te

Maxwells Relations

ht
tp
:/
/k
er
al
a

1
...
dH = TdS + VdP
3
...
dG = VdP SdT
...

These four derivatives are very well known relations, which have extensive applications
in both physical and chemical phenomena
...

We have,
dG = Sdt + VdP
= O + VdP (at constant, T)
∴

∆G = G2 G1 =

z

2

1

Vd P

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH4-2
...
c
ot
og

ENGINEERING CHEMISTRY

Applying this to one mole of an ideal gas (PV = RT), we get,

µ2 µ1 = RT ln

bl
y
...

P1

it

G2 G1 = RT ln

rs

Since G2 and G1 are molar free energies µ2 and µ1 respectively, µ1 becomes µφ0 if we
apply the standard conditions i
...
, pressure 1 atmosphere
...

Gibbs-Duhem Relations

ca

lu

The free energy G of a system is a state function, that is, G depends upon P, T and V
...
Let us have a system containing n1
moles of A1, n2 moles of A2, etc
...
)

The term

F ∂G IJ dT + FG ∂G IJ
G ∂T K
H
H ∂n K
F ∂G I = V FG ∂G IJ = S
...

FG ∂G IJ
H ∂n K

P, ni

1 P, T , n , n
2
3

dn1 +

2

P, T, n1 , n3
...

dn2
...

= ∑µi dni

...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH4-2
...
c
ot
dG = µ1n1∆x + µ2n2∆x +
...

G∆x = µ1n1∆x + µ2n2∆x +
...

or,

ve

Hence,
G = µ1n1 + µ2n2 +
...
= ∑µini
Now, complete differentiation of this equation gives us,

it

dG = G∆x

rs

hence,
So, we have,

y
...
) + (n1dµ1 + n2dµ2 + n3dµ3 +
...
= 0
We have thus three useful relations for chemical potentials with the composition of the
system,

gi

(i) G = µ1n1 + µ2n2 + µ3n3 +
...
= ∑µdn

lo

(iii) 0 = n1dµ1 + n2dµ2 + n3dµ3 +
...

We, know,

...

dq = dE + PdV and dS = dq/T

ht
tp
:/
/k
er
al
a

So,
Again,

te

ch

no

Deduction of Vant Hoffs reaction isotherm (Application of thermodynamics to
homogeneous equilibrium or thermodynamics of chemical equilibrium):
Let us consider a general reaction
aA + bB → cC + dD
G = H TS = E + PV TS

∴
dG = V
...
dT
At constant temperature,
(dG)T = V
...

Free energy change for one mole of any gas at a constant temperature is given by:
dG = V
...
T

Integrating both sides,

dP
P

LMQ
N

PV = RT or V =

z

RT
P

O
P
Q

dP
P
So,
G = G0 + RT ln P

...
e
...

Let the energy/mole of A, B, C and D at their respective pressures PA, PB, PC and PD are
GA, GB, GC and GD, respectively
...
(iii)
∫ dG = RT

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH4-2
...
c
ot
og

ENGINEERING CHEMISTRY

Substituting the values of GA, GB, GC and GD from (ii) and (iii), we have

∆G0 = RT ln

So,

(PA ) a (PB ) b

LM (P ) (P ) OP
NM (P ) (P ) QP
C
A

c

a

D

B

d

b

it

(PA ) a (PB ) b

rs

(PC ) c (PD ) d

+ RT ln

Now, at equilibrium, ∆G = 0

+ RT ln

(PC ) c (PD ) d

...

bl

∆G = (cGC0 + cRT ln PC + dGD0 + dRT ln PD)
(aGA0 + aRT ln PA + bGB0 + bRT ln PB)
(cGC0

eq

gi

ca

∆G° is the difference in free energy between the products and the reactants
...
(v)

lo

∴

LMwhere K
MN

no

Combining (iv) and (v), we have

te

ch

∆G = RT ln Keq + RT ln

∆G = RT ln Keq RT ln

(PC ) c (PD ) d

(PA ) a (PB ) b

(PC ) c (PD ) d

(PA ) a (PB ) b

ht
tp
:/
/k
er
al
a

or,

...
It is of great importance as it
gives a quantitative relation for free energy change accompanying a chemical reaction
...

Highlights:

• ∆G° = RT ln Keq when pressures of reactants and products are one (i
...
, P = 1)
...

• The above relation shows that equilibrium constant (Keq) can be calculated from a
table of standard free energy values
...
One gm of water requires 536 calories of heat for conversion to steam at
100°C
...

Sol
...
902 Kcal mol1
...
blogspot
...
PM5

92

sp

92

...
2
10 3

w = 8
...
36 × 10 9
kJ = 0
...
158 0
...
332 kJ
...
13

it

Here

y
...
We have,

bl

Example 2
...
36 × 109 ergs, after absorbing 990 cals
...
Calculate the internal energy change of the system
...
Calculate the work done by the following reaction at 27°C
...
Here,

lu

Zn + H2SO4 → ZnSO4 + H2↑

1 mol
...
314 × (273 + 27) =

[Q V1 = 0]
[Q n = 1]

8
...

1000

lo

= 2
...

no

Example 4
...
(Given qv
at 200°C is 97000 cals)
...

Here

C(s) + O2(g) = CO2(g)
qv = 97000 cal
...

We have,

qp = qv + ∆nRT
...

qp = qv (As n2 = n1)

Example 5
...

Sol
...

Here,

∆n = 1 2 = 1, T = 500 K

∴

R = 2 cal deg1 mol1 = 2 × 103 Kcal deg1 mol1
∆E = ∆H ∆nRT = 109 ( 1) × 2 × 103 × 500
= 108 Kcal
...
Heats of combustion of ethylene, hydrogen, and ethane are 337
...
3, 372
...
Calculate the heat of reaction of C2H4(g) + H2(g) →
C2H4(g) at that temperature
...
blogspot
...
PM5

93

...
Given,
(i) C2H4 + 3O2 → 2CO2 + 2H2O,

7
O,
2 2

∆H = + 372
...

ni

Adding the equations (i), (ii) and (iv) we have,

ca

lu

1
7
O + 2CO2 + 3H2O → 2CO2 + 2H2O + H2O + C2H6 + O2
2 2
2

C2H4 + H2 → C2H6,

∴

it

∆H = 372
...

∆H = 68
...

7
O → 2CO2 + 3H2O,
2 2

C2H4 + 3O2 + H2 +

bl

1
O → H2O,
2 2

(iii) C2H6 +
or,

∆H = 337
...

ve

(ii) H2 +

(∆H = 32
...
7 Kcal
...
Calculate OH bond energy from the following heats of reactions
...
(i)

O2(g) → 2O(g),

∆H = 120 Kcal

...
(iii)

lo

H2(g) → 2H(g),

no

1
O (g) → H2O(g),
2 2
Sol
...
e
...

1
O (g)
2 2

∆H = 58 Kcal
...

We know that, there are two OH bonds in a molecule of water, and for breaking of
these two bonds energy requirement is 222 Kcal
...

∴ OH bond energy is 111 Kcal
...
Calculate the enthalpy of formation of propane (C3H8 ) at 298 K
...

C

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH4-2
...
c
ot
og

3CO2(g) + 4H2O(l )

ve

According to Hesss law ∆H1 = ∆H2 ∆H3

it
rs

2
DH

DH

3

C3H8(g) + 5O2(g)

y
...
A thermodynamic cycle is drawn:

3C(s) + 4H2(g) + 5O2(g)

ni

∆H1 = ∆H °f (C3H8)

lu

∆H2 = 3 ∆H ° (C) + 4 × ∆H ° (H2)
...

ls

ca

DH

3

Red P

H3PO4

21

ls

ca

13

2

ht
tp
:/
/k
er
al
a

DHT (DH1)

DH

86

23

te

ch

no

Example 9
...

Sol
...

Example 10
...
If average Cp for water and steam are 1 cal g1 and 8
...

Sol
...

∆H150° =?; ∆H100° = 538

Cp for water = 1; Cp for steam =

8
...

18

∆Cp = 0
...
55
...

∆H2 ∆H1 = ∆Cp(T2 T1)

∆H150° ∆H100° = 0
...
blogspot
...
PM5

95

sp

95

THERMODYNAMICS

...
55 × 50

bl

= 538 0
...
5 cal g1
...

Example 11
...

2
1

ni

= 1
...
66 kJ
...
303 × 8
...
303 RT ln P
2

Sol
...
Calculate the change of molar entropy during melting of ice
...
14 J g1
...

19
...
26 J mol1
...
Calculate the change of molar entropy during the conversion of liquid
oxygen to oxygen gas at its b
...
( 182
...
Given L = 12
...

lo

gi

=

qrev
T

no

dS =

=

te

ch

Sol
...
19 × 32
12
...
33 J mol1
...
9)
90
...
Calculate change of entropy in isothermal reversible expansion of one mole
of an ideal gas
...
We know that

∆E = 0

Therefore,

q = W = RT ln
dS =

V2
V1

V2
qrev
= R ln
V1
T

[Positive quantity]

Example 15
...
5 cal g 1
...
Here,

P1 = 528 mm of Hg; P2 = 1 atm = 760 mm of Hg
...
5 cal g1
= 545
...

R = 1
...

From the integrated form of Clausius-Clapeyron equation, we have

LM
N

P2
∆H v
1
1
−
log P =
2
...
blogspot
...
PM5

96

sp

96

...

LM 1 − 1 OP
N T 373 Q
1

y
...
1582 =
2
...
987
528

og

log

bl

∴

ni

ve

rs

it

Example 16
...
(i) Since operation is isothermal and the gas is ideal so, ∆E = 0
...

But, for a reversible process, work done by system,
W = P(V2 V1)
= 1 atm (20 10) dm3 = 10 atm dm3 = 10 atm L

lu

FG 8
...
7 J
...
0821 L atm K

ca

= 10 L atm ×

q = W = 1012
...

∆H = ∆E + P∆V = 0 + 1012
...
7 J
...
A gas during expansion from 10 litre to 20 litre under 2 atmospheric
pressure absorbs 300 cal
...
Find the change in internal energy
...
Work done in an irreversible process is given by
W = P(V2 V1) = 2(20 10) = 20 lit
...

= (20 × 24
...
atm = 24
...

From the 1st law of thermodynamics,
q = ∆E + W
or,
∆E = q W = (300 485) cal = 185 cal
...

Example 18
...
Pressure is increased reversibly upto 7 atm and temperature is incremented
to 90°C
...

Sol
...

363
1
+ 2 × ln
= 2
...

300
7
Example 19
...
49 × 102 atm1
...

1
3
N (g) + H2(g)
NH3(g) + 11
...

2 2
2
Consider the reaction to be independent of heat and temperature
...
blogspot
...
PM5

97

sp

97

THERMODYNAMICS

...
From Vant Hoff equation, we have

bl

T1 = 27°C = 300 K; T2 = 37°C = 310 K
...

LM
N

K P2
∆H T2 − T1
ln K
=
R
T1T2
P1

K P1 = 3
...
49 × 10 −2

=

OP
Q

ve

LM
N

310 − 300
− 11200
2
...
987 300 × 310

lu

log

OP
Q

ni

LM
N

K P2
T2 − T1
∆H
log K
=
2
...
2 Kcal = 11200 cal; R = 1
...

∴

K P2 = 1
...

gi

ca

or,

lo

SHORT QUESTIONS AND ANSWERS
Q
...
State First law with mathematical expressions
...
See text page 68
...

Q
...
State intensive property of a system
...
See text page 66
...
3
...
Internal energy and ethalpy of a system are measured by keeping the volume and
the pressure constant, respectively
...

Q
...
The molar heat of sublimation of a solid is always greater than the molar
heat of vaporization of the corresponding liquid
...
Since the molar heat of sublimation is the summation of heat of melting and heat
of vaporization so it is always greater than the heat of vaporization of the corresponding liquid
...
5
...
The entropy of a substance becomes zero when the substance is perfectly crystalline
i
...
, ordered state and at the temperature of 0 K
...
6
...

Ans
...

Q
...
Derive Gibbs-Helmholtz equation and mention its significance
...
See text page 85
...
8
...
See text page 71
...
blogspot
...
PM5

98

sp

98

...

bl

Q
...
What do you mean by entropy?
Ans
...
e
...
Its change
q
i
...
, dS is defined as dS = reversible
...
10
...
The first law does not indicate:

ve

rs

(i) Whether the transformation of intrinsic energy of a substance would occur at all
...

lu

or ∆E = 0 W

[Q q = 0]

ca

q=0
∆E = q W

So, from first law,

ni

Q
...
Apply the first law of thermodynamics for the following cases (a) adiabatic
change, (b) cyclic process
...
(a) For adiabatic change

gi

So,
W = ∆E
So, in adiabatic process, the work done by the system is equal to the decrease in internal
energy
...
e
...

So, from first law,
∆E = q W

te

ch

no

or
0=qW
[Q ∆E = 0]
or
W = q
...

ht
tp
:/
/k
er
al
a

Q
...
Define reversible and irreversible processes
...
See page 69
...
13
...

Ans
...

(a) Heat exchange between the system and the
surrounding does not occur
...

place
...

(c) PVγ = constant for such process
...
14
...

V2
P1
Ans
...

1
2
Q
...
Write the expression for work obtained in an isothermal irreversible
reversible process
...
Wirr = P2(V2 V1)
...
blogspot
...
PM5

99

...
16
...
State relation between them
...
18
...
See page 72
...
20
...

ni

Ans
...

ve

rs

Q
...
State with example the significance of Hesss law
...
See page 71
...

Q
...
Explain that Joule-Thomson experiment is isoenthalpic
...
See page 73
...
See page 81
...
21
...

ca

Ans
...

Q
...
State the second law of thermodynamics
...
See page 84
...

lo

Q
...
What do you mean by a cyclic process?

no

Ans
...

Q
...
State Maxwells relations
...
See page 89
...
25
...

te

Ans
...

ht
tp
:/
/k
er
al
a

Q
...
How can you measure a spontaneous system with the help of free energy?
Ans
...

Q
...
What do you mean by ∆G° for the reaction H2 +

at 25°C?

1
O = H2O is 54
...
65 Kcal
...
It means that if a mole of H2 and

1
...

(ii) Derive Clapeyron-Clausius equation and state its applications
...
Describe a relation between the two
...
It is based on which law? Explain
...
blogspot
...
PM5

100

sp

100

...

bl

(vi) What is Joule-Thomson effect?
(vii) What is bond energy? How can you calculate the bond energy of CC bond in ethane?
(viii) Write notes on (a) Heat of formation, (ii) Heat of combustion
...

(x) Why is entropy a state function?
2
...

(ii) Which is an extensive property?
(a) Temperature
(b) Viscosity
(c) Volume
...

(iv) When is a system in equilibrium?
(a) ∆G is zero
(b) ∆S is minimum
(c) ∆G is maximum
...

(b) Only H+ and OH ions react in each case
...

(vi) The expression of first law of thermodynamics is
(a) q = ∆H W
(b) ∆H + P∆V = ∆E
(c) ∆E = q W
...

(viii) All living systems are
(a) adiabatic systems
(b) Closed systems
(c) Open system
...
During melting it
(a) decreases
(b) increases
(c) remains unchanged
...

3
...

(c) Give the mathematical expression for first law of thermodynamics
...
(a) What is Joule-Thomson effect?
(b) Prove the constancy in Joule-Thomson expansion
...
Derive an expression for the work done during reversible isothermal expansion of an ideal gas
...
(a) Show that for a gaseous expansion, ∆H > ∆E
...

(c) Prove that Cp Cv = R
...
Derive Kirchoff s equation
...
(a) What do you mean by entropy?
(b) Give physical significance of entropy
...

(d) Explain the relation: S = k ln w
...
Derive an expression for entropy for an ideal gas
...
Show that entropy change in an irreversible process is positive
...
blogspot
...
PM5

101

...
Show that entropy change for an irreversible isothermal expansion of an ideal gas is positive
...
Entropy change for the mixture of gases can be represented by
where xi = mole fraction of gas
...

13
...
(a) State Hesss law
...

it

(b) What do you mean by free energy (G)?

ni

(c) Explain the terms (i) Heat of reaction, (ii) Heat of combustion, (iii) Heat of neutralisation,
(iv) Heat of formation, (v) Heat of solution, (vi) Heat of fusion, (vii) Heat of vaporisation,
(viii) Heat of sublimation
...
How can you determine the bond energy and lattice energy with the help of Hesss law?
16
...

17
...

ca

(b) Give the significance of Gibbs-Helmholtz equation
...
(a) How can you determine spontaneity of changes of a system?
(b) What do you mean by chemical potential (µ)?

lo

(c) Show that chemical potential does not change during phase transfer of a compound
...
Derive Maxwells relation and state its usefulness
...
Derive an expression for chemical potential at a temperature T in terms of P
...
Derive Gibbs-Duhem relations
...
g1
...
82 and of
water of unity
...

ht
tp
:/
/k
er
al
a

1
...
What do you mean by Vant Hoff reaction isotherm? Derive an expression for the reaction isotherm
lL + mM +
...

2
...
1 cals; 1440 cals; 1440; cals; 4
...
T
...
are heated inside a gas cylinder to 100°C

assuming it to behave ideally and having Cv =

3
R
...
133
...
1 cals]

3
...
36 × 109 ergs work after absorbing 990 cals
...

Find the internal energy change of the system
...
790 cals]

4
...
Considering the gas to be an ideal find out the work obtained in this case
...

[Ans
...
788 × 107 ergs]

During isothermal reversible expression of 4 g of helium gas at 27°C the pressure reduces from
10 atm to 1 atm
...
Consider the gas to behave like an ideal
...
1381
...

The heats of formation of CO2 from diamond and graphite are 94500 and 94050 cal, respectively
...
450 cal]

7
...
05 and 68
...
The heat of formation of
ethyl alcohol is 66
...

[Ans
...
6 Kcal]

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH4-2
...
c
ot
og

Find heat of formation of caustic soda from the following data:

1
H + 98,000
2 2

y
...

1
O = H2O + 68,380
2 2
NaOH + water = NaOH (aq) + 13,300
...
153080 cals]
9
...

[Ans
...
Isothermally at 27°C one mole of a van der Waals gas expands reversibly from 2 litres to 20
litres
...
42 × 1012 dynes cm 4 mol1 and b = 30 c
...

LM
N

ve

rs

it

H2 +

O
P
Q

L
M
N

O
P
Q

20 − 0
...
42 × 1012
2 − 0
...
303 × 8
...

+a
−
V1 − b
V2 V1

[Hint
...
]
11
...
It was allowed to expand isothermally
against a constant external pressure of one atmosphere
...

[Ans
...
5 Kcal; 1
...
From the following bond enthalpies calculate ∆H for the reaction, H2 + Br2 → 2 HBr
...
24 kJ mol1; BrBr bond energy = 192
...
108
...
3 kJ mol1
...
The heat of combustion of methyl alcohol is 173
...
Given, ∆H(H O, l) = 68320 cal;
2

∆H f (CO2 , g) = 94050 cal
...
[Ans
...
Calculate ∆S, ∆A and ∆G for vaporisation of 2 moles of benzene (b
...
= 353
...
∆S = 44
...
4 Kcal]
15
...
59 litre2 atm/mol2 and b = 0
...
What is
the inversion temperature of the gas?
[Ans
...
The sp
...
39
...
0 kg of benzene at 30°C
...
0
...
Calculate the entropy change in vaporisation of ether
...

[Ans
...
1 eV]
18
...
Given, ∆G°298
= 71
...

(Ans
...
43 Kcal/mol1]
19
...
5 Kcal
...

[Ans
...
75 eV]
20
...
The average latent heat of vaporisation of
water is 546 cal g 1 within the temperature range 90°C 100°C
...

[Ans
...
blogspot
...
PM5

103

sp

103

THERMODYNAMICS

...

it

5

ve

rs

Reaction Dynamics/Chemical Kinetics

ni

INTRODUCTION

ch

Velocity of Reaction

no

lo

gi

ca

lu

From the study of chemical equilibrium involving law of mass action, we can predict how far
the reaction would go
...
Though
thermodynamics has got an enormous influence in chemical equilibrium yet has no valid
application in studying the rate of reaction
...
The velocity of a reaction is not same even at
constant temperature
...

Modern techniques have been developed to study the reaction rate which gets completed in
milliseconds or even in microseconds
...
As for
example:
CH3COOC2H5 + H2O → CH3COOH + C2H5OH
2H2O2 → 2H2O + O2

ht
tp
:/
/k
er
al
a

te

From law of mass action, we know that the rate of reaction is dependent on the active
masses of reacting substances
...

For a reaction → aA + bB
cC + dD
rate of reaction, (r) →
r = k
...
[B]b
where [A] and [B] are the concentrations of the reactants at that instant
...

When
[A] = [B] = 1
then,
k = r
...
e
...

Highlights:
• Higher the value of k higher the reaction rate
...

• The rate of a reaction can also be determined by the increasing concentration of
the products in unit time
...

104
http://keralatechnologicaluniversity
...
com

...

y
...

Therefore, the rate equation will involve the concentration of the reactants
...
As for example, for a reaction:
aA + bB → Products

ve

rate of the reaction (r) = k
...
[B]b
...

The experimentally determined rate equation for the decomposition of H2O2 is:

lu

r = k
...
So it is
a first order reaction
...
1

Experimentally determined
rate

lo

Reactions

no

(i) 2HI = H2 + I2
(ii) H2 + I2 = 2HI

r = k
...
[H2][I2]

2

r = k[CH3COOC2H5] [NaOH]

2

te

ch

(iii) CH3COOC2H5 + NaOH
= CH3COONa + C2H5OH

Order

ht
tp
:/
/k
er
al
a

Highlights:

• The number of molecules of the equation for the chemical change has got no relation
with the order of a reaction
...

• The order of a reaction may be zero or fraction
...
As for example
2HI = H2 + I2

For this reaction, minimum two molecules of HI will be required
...
Again for the reaction:
2H2O2 = 2H2O + O2
But the reaction can be written as
H2O2 = H2O + O
So, for decomposition of H2O2, one molecule is needed and hence the molecularity is one
...
blogspot
...
PM5

105

...
[NO]2 [O2]

rs

•

it

The observed rate = k
...

y
...

• For the reaction

lu

ni

BrO3 + 5Br + 6H+ = 3Br2 + 3H2O
The observed rate = k
...

• For the reaction

gi

CO + Cl2 = COCl2
Rate = k
...
5

lo

So, the order of the reaction is 2
...

Mathematical Formulation of First Order Reaction

ch

no

The reactions, where the experimentally determined rate of the reaction is dependent
on the first power of the concentration of the reactant, are called first order reactions
...

dt

k = rate constant
...

(a x)
x
At time t, a = initial concentration of A
...

Therefore, the rate equation will be

dx
= k
...
dt
...
blogspot
...
PM5

106

...
ln
t
a− x
2
...
log
=

...
ekt
x = a(1 ekt)
...

or

lu

a
is a common ratio, it is purely a dimensionless number
...

1
a
(ii)
k =
...

t
a x
So, unit of k will be time1
...

(iv) From the equation,
1
t =
...
ln
a
2
k
a
2
1
=
...
303
0
...
log10 2 =
=

...

So, a first order reaction is never completed
...
e
...
ekt
k
Therefore,
log c =
+ log c0
2
...

2
...
blogspot
...
PM5

107

sp

107

REACTION DYNAMICS/CHEMICAL KINETICS

...

bl

Examples of a First Order Reaction
(i) Decomposition (gas phase)
(a)
2N2O5 → 4NO2 + O2
(b)
N2O4 → 2NO2
(c)
CH3CH2Cl → C2H4 + Cl2
CH 2  CH 2


(d)
→ 2C2H4
CH 2  CH 2
ethylene

ve

cyclobutane

CH2¾CH2 ¾¾® CH3CH = CH2
propylene

lu

CH2

cyclopropane

CH  CH 2 → CH2 = CHCHe = CH2
1, 3-butadien
...

Let, the reaction be represented by,
A + B → C + D
Initial concentration of A = a
Initial concentration of B = b

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH5-1
...
c
ot
og
bl

Decrease in concentration of A and B at time t = x
Concentration of A at time t = a x

y
...
303
a(b x)
log
(b a)t
b(a x)

If, initially, concentration of both the reactants are equal i
...
, a = b, then we can write,

dx
= k(a x)2 or
dt

dx
= k(b x)2
dt

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH5-1
...
c
ot
og

ENGINEERING CHEMISTRY

bl

Taking

( a x) 2

= k dt

it

dx

or

y
...

if we put a x = c
t a(a − x)

or k =

kt =

1 1

c a

1
1
= kt +
...

=
=
k a(a x) k a(a a / 2) ak
i
...
, half decomposition time of a second order reaction is inversely proportional to the first
1
power of initial concentration and is equal to
when a = 1
k
(ii) Unit of rate constant k

ht
tp
:/
/k
er
al
a

te

ch

no

t1/2 =

dx
= k(a x)2 = kc2 when (a x) = c
dt

dx 1 conc
1

...
time1 = l
...
e
...

Examples of a Second Order Reaction
(i) Decomposition (gas phase):
(a)

sp

110

2HI → H2 + I2

(b)

2NO2 → 2NO + O2

(c)

2NOCl → 2NO + Cl2

(ii) Displacement reaction (gas phase):
(a)

H + D2 → HD + D

(b)

Cl + H2 → HCl + H

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH5-1
...
c
ot
og

(iii) Dimerisation (gas phase):

y
...

c

Unit of k

sec1

l mol1
...

Dependent on concentration
...

Inversely proportional to initial
concentration
...
of moles of each reactant decomposed at time t = x
...
blogspot
...
PM5

111

sp

111

REACTION DYNAMICS/CHEMICAL KINETICS

...

dx
= k(a x)3
dt
dx
= k dt
( a x) 3

Again

rs

Integrating,

2

no

∴

lu

OP
Q
1 O 1 x (2a x)

P = t 2 a ( a x)
a Q

1
1
1
2
2
2 (a x)
a

lo

kt =

ca

L
M
N
1 L
k=
M 1
2t N ( a x)

∴

2a2

gi

or

1

Z=

(Integration constant)

ni

ve

1
1

...

=Z ∴
2 a2
1
1
1

= kt
2 ( a x) 2 2a 2

2

2

2

...
2a a
a 2 a2
a
1 2
1
1 4
2
4
=
=
k=
...

a
2
2
2
13 1
3
1
1 3 1

...

=
or t =
...

(ii) k is dependent on the unit of concentration
...

FG
H

FG IJ
H K

IJ
K

Examples of Third Order Reaction
(i)
2NO + O2 → 2NO2
(ii)
2NO + Cl2 → 2 NOCl
(iii)
SnCl2 + 2FeCl3 → SnCl4 + 2FeCl2

Zero Order Reactions

There are certain reactions where rate of reaction does not diminish with time i
...
, the
rate of the reaction is not dependent on the concentration of the reactant or, in other words,
rate of the reaction is proportional to the zero power of the concentration of the reactant i
...
,

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH5-1
...
c
ot
og

dc
= k[ A ]0 = k
dt
where concentration of the reactant A = c

[Q [A]0 = 1]

c0

dc =

t

0

k dt = k

z

t

0

y
...
e
...
e
...

ca

lu

ni

k=

dc
is constant
...
The bromination of acetone in acid solution
is of zero order with respect to Br2; since the reaction velocity is not influenced by a change in
concentration of bromine
...

In those reactions, the rate of reaction is proportional to fractional power of concentration of
the reactant, i
...
,

dc
= Kc1/n
dt
where concentration of the reactant = c
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH5-1
...
c
ot
og

ENGINEERING CHEMISTRY

Pseudo Unimolecular Reactions

bl

Let us take the reaction
Sucrose

Glucose

y
...

So, the reaction is dependent on the concentration of both the reactants
...
ln
t
a x

lo

or

gi

ca

dc
= k′[C12H22O11]
dt
dx
= k′(a x)
dt

lu

ni

ve

dc
= k[C12H22O11] [H2O]
dt
In solution the amount of water is excessively high compared to sugar
...
So [H2O] is constant
...
Due
to presence of excess water, the incident so happens
...
Other pseudo unimolecular reactions are:

te

(i) COS + H2O → CO2 + H2S
(ii) CH3COOCH3 + H2O → CH3COOH + CH3OH

ht
tp
:/
/k
er
al
a

(iii) (CH3CO)2O + 2C2H5OH (excess) → 2CH3COOC2H5 + H2O

Methods for the Determination of the Order of a Reaction
(i) Substitution methods (with the help of rate equations)
The following are the expressions of rate constants for different reactions:
First order reaction

⇒

k=

a
1
ln
t
a x

Second order reaction

⇒

k=

x
1

...
e
...
By putting the value a and (a x) the value of k
is determined
...
The method is laborious and too complicated to give a
satisfactory constant value
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH5-1
...
c
ot
og

(ii) Half-life method

lo

gi

ca

lu

ni

ve

rs

it

y
...
693/k (fixed)
Second order = 1/(ak)
Third order = 1/(a2k′)
In separate sets of experiments if different concentrations are taken and t1/2 are measured
the order can easily be determined
...
e
...
1/a will give a straight line
...
1/a2 gives a straight line, the reaction is of
third order
...

For, the first experiment the initial concentration = c1
...

So, the rate equations for the two experiments will be
dc
R1 = 1 = kc1n;
dt
dc2
R2 =
= kc2n
...

(iv) Graphical method
If we plot time vs a function of concentration, we can get the order of a reaction
...
If a plot of 1/c vs t
gives a straight line the reaction is of second order and if the plot of 1/c2 vs t gives a straight
line the reaction is of third order (Fig
...
1 (a) and (b))
...
5
...
blogspot
...
PM5

sp

115

REACTION DYNAMICS/CHEMICAL KINETICS

115

...

bl

The reaction which takes a single path has no interfering influence in the main reaction
...
The rate constant values are not obtained constants for a number
of reactions
...
Some of these factors are given below:

rs

Simultaneous Reactions

ca

lu

ni

ve

In a simple reaction, the reactants react to give products
...
The other reactions occur simultaneously
...
These reactions interfere to give a constant value of k
...

Simultaneous reactions

Side reactions

Opposing reactions

Consecutive
reactions

ch
te

B + C; yield 90% (main reaction)
P + Q; yield 10% (side reaction)

CH2 = CH2

ht
tp
:/
/k
er
al
a

Example:

no

lo

gi

(a) Side reaction: Sometimes the reactants undergo two or more independent reactions
simultaneously
...
The reaction which gives the major
product is called main reaction and the other is called side reaction
...
CH2
...
CH2OH

C2H4 + H2O

C2H5OH

dx
= k1c
dt

dy
CH3CHO + H2
= k 2c
dt

[k1 and k2 are not same]

(b) Opposing reaction: The reversible reactions also interfere to give the constant value of k
...

Example:
CH3COOH + C2H5OH

k1
k2

CH3COOC2H5 + H2O

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH5-1
...
c
ot
k2

CH2

og
bl

(Hydroxy butaric acid)

O¾CO
+ H2O

CH2¾CH2

y
...
CH2
...
COOH

k1

it

(Lactone)

Rate equation for the first reaction is:

ca

lu

ni

ve

rs

dx
= k1(a x)(b x) k2 x2
...

(c) Consecutive reaction: In many reactions, the products obtained change to a third
product
...

k1

k2

gi

A → B → C
Examples:

lo

k1

k2

(CH3)2O → CH34 + HCHO → CO + H2
k1

no

(i)

(ii) 2NO + H2 → N2 + H2O2
k2

ch

H2O2 + H2 → 2H2O

ht
tp
:/
/k
er
al
a

te

(iii) CH 2
...
COOC2 H5
CH 2 COONa
Ethyl Succinate

+ C2 H 5 OH

Ethyl Sodium Succinate

CH 2 COOC 2 H 5
CH 2COONa
k2

+ NaOH → 
+ C 2 H 5OH
CH 2 COONa
CH 2 COONa
Sodium Succinate

(iv) H2O2 + 2HI → 2H2O + I2
k1

H2O2 + I → H2O + IO
k2

IO + 2H+ + I → H2O + I2
Of these reactions, the first proceeds very slow, which can be measured and that
determines the order of the reaction
...
After some time the reaction starts and proceeds as
usual with normal speed
...

As for exampleperiod of induction is noted during the reaction of H2 and Cl2 in the presence

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH5-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

118

bl

of light
...

Generally, negative catalysts are responsible for this inactivity in the period of induction or
sometimes slow production of an active intermediate
...

Effect of Temperature on Reaction Rate (Arrhenius Equation)

rs

it

Temperature has a great influence on reaction rate: Arrhenius studied the fact and
concluded that rate of every reaction increases with increase of temperature
...

1
a straight line is obtained
T

ni

He established that when loge k or ln k is plotted against

ve

Keeping concentration constant if we increase the temperature, rate of a reaction will
increase i
...
, value of k will increase
...

lu

(Fig
...
2)
...
5
...

The relation can be expressed mathematically as follows:
ln k = A

E
RT

E
d ln k
=
RT 2
dT

or

where A and E are constants
...

Let, rate constant of a reaction at temperature T1 = k1 and rate constant of that reaction
at temperature T2 = k2
...
blogspot
...
PM5

118

...
303R T1 T2

og

log

OP
PQ

bl

or

it

y
...
If E for a reaction is known, we can determine the value of k2 when k1
is known
...

ve

• Temperature coefficient of a chemical reaction is defined as the ratio of two rate
constants of the reaction at two temperatures differing by 10°
...

• The exponential form of the above equation is known as Arrhenius equation

lo

gi

ln k = a

−

ht
tp
:/
/k
er
al
a

te

ch

no

E /RT
...

Arrhenius equation describes how the rate constant for a reaction varies with
temperature and makes it possible to determine the activation energy for the
reaction
...
For every reaction, the molecules should be raised to a state of sufficient energy, otherwise
the reaction will not be

Potential energy

Ea

A+B

DH

A+B

C+D

C+D

Progress of reaction

Fig
...
3

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH5-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

120

y
...
This energy state is different for different reactions
...
Some molecules are more energised than the others
...

rs

it

These activated molecules take part in the reaction, others cannot take part in the reaction
unless activated
...
When
the liberated energy is less than Ea, the reaction becomes endothermic and when the liberated
energy is greater than Ea the reaction becomes exothermic (See Fig
...
3)
...

lu

• There is always an equilibrium between ordinary molecules and excited or activated
molecules with an energy difference Ea
...

lo

Collision Theory

ht
tp
:/
/k
er
al
a

te

ch

no

According to this theory, the molecules of the reactants collide to take part in a reaction
...
Number of collisions per second (z) in any given volume can be obtained from kinetic
theory
...
It is observed that the number of molecules reacted is always
less than the number of molecules collided i
...
, every collision does not give rise to reaction
...
According to Maxwell, at a temperature T, the ratio of total
number of collisions and the number of collisions giving E to the molecules is eE/RT
...

∴ Number of collisions of molecules possessing E = z
...

These number of molecules will react
...
eE/RT
...
So, the theory of collision can be
accepted
...

• The collisions, which lead to the reaction, are called effective collisions
...

• Not only effective collisions are responsible for a reaction, but orientation of collision
is also important
...
blogspot
...
PM5

120

...

Collision

+

bl

og

sp

121

REACTION DYNAMICS/CHEMICAL KINETICS

lu

Ineffective
Ineffective

ca

Fig
...
4

gi

Rate of a reaction = [No
...

lo

SOLVED EXAMPLES

te

ch

no

Example 1
...
So, it is
added colloidal gold and at interval of 5 minutes an aliquot (5 ml) is taken and cooled in ice
cold water and titrated against standard KMnO4 solution
...
e
...
Determine from the following data the value of k and establish
that the decomposition is of the Ist order
...
1

5
37
...
8

20
19
...
For a Ist order reaction

a
1

...
1
t=5
k=

Here,
Now, putting

at
at
at
at

1
10
1
t = 20, k =
20
1
t = 30, k =
30
1
t = 50, k =
50
t = 10, k =

k=

1
46
...
ln
= 0
...
1

46
...
0436 min1
29
...
1
ln
= 0
...
6
46
...
044 min1
12
...
1
ln
= 0
...

5
...
blogspot
...
PM5

121

30
12
...
0

...

bl

Since the k values are fairly constant by putting the data in the Ist order-rate equation
the reaction i
...
, decomposition of H2O2 is of the Ist order
...
A 20% sugar solution is taken
...
The mixture is poured in a polarimeter tube
...
The
data is given below:
The optical rotation of sucrose in 1(N) HCl at various times is given in the following
table:
Time (in minute)
0
7
...
05
α
Rotation (degrees)
+ 24
...
4
+ 17
...
74
Show that the reaction is of the Ist order
...
Here,
a = r0 rα
(a x) = rt rα
where r0, rt and rα are initial rotation, rotation after time t and rotation after infinite time
where the reaction is assumed to be completed
...
09 + 10
...
83

lo

1
34
...
00486 min1
7
...
14
1
34
...
14
k=
= 0
...
14
1
34
...
05
25
...
00485 min1
...
05
25
...
e
...

Example 3
...
5(N) HCl kept
at a temperature of 25°C
...
The data are as follows:
Time ( in minutes):
0
75
119
183
α
Vol
...
24
24
...
60
29
...
03
From the above data show that the hydrolysis is of the Ist order
...
Here
a = Vα Vo
a x = Vα Vt
where Vo, Vt and Vα are the volumes of alkali initially, after a time t and after an infinite time,
respectively
...
03 19
...
79
Time
Vα Vt
k
2
...
79
75
17
...
00395 min1
75
17
...
303
22
...
43
k=
= 0
...
43
2
...
79
log
183
12
...
00316 min1
183
12
...
14

k=

ht
tp
:/
/k
er
al
a

te

ch

no

7
...
blogspot
...
PM5

122

...
e
...

y
...
A Ist order reaction is 25% completed in 30 mins
...

a
2
...
log
t
a x
t = 30 min a = 100%
a = (100 25)% = 75%

k=

2
...
0095 min1
30
75

ve

Here,

rs

k=

0
...
Time of 50% reaction, i
...
, t1/2 to be determined for Ist order reaction t1/2 is

lu

0
...
9 minutes
...
0095
Example 5
...
Calculate the rate constant
and time for 75% completion of the reaction
...
693
k
= 17 mins
...
We know

gi

ca

∴

no

0
...
0407 min1
17
a = 100%
a x = (100 75)% = 25%

∴

k=

te

ch

Here,

2
...
303
2
...

log
∴
t=
=
0
...
The half-life for radium is 1600 years
...

ht
tp
:/
/k
er
al
a

∴

k=

Sol
...
693
k
0
...
693
k=
year1 = 0
...
303
log
k=
t
ax
a = 100 %
(a x) = 100 80 = 20
t1/2 =

t=

2
...
17 yrs
...
000433
20

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH5-2
...
c
ot
og

ENGINEERING CHEMISTRY

sp

124

0

5

15

25

Vol
...
24

6
...
32

it

Time (in minute)

Sol
...
41

ve

x
1
at (a x)

ni

a = 16 c
...

ax

x

5

10
...
76

k=

15

6
...
87

25

4
...
41

lu

T

ca

Here

35

rs

Show that the reaction is of the 2nd order
...

bl

Example 7
...

An aliquot (25 cm) of the reaction mixture was titrated against a standard acid at regular time
intervals
...
76
×
= 0
...
24

1
9
...
0067 conc1 sec1
16 × 15 6
...
68

k=

1
11
...
0069 conc1 sec1
16 × 25 4
...
59

k=

1
12
...
0066 conc1 sec1
16 × 35
3
...
e
...

Example 8
...

ht
tp
:/
/k
er
al
a

Sol
...

The rate equation is

d[ A ]
= k
...
So the concentration of A at time t is (a x)
...
t
n1
(n 1) ( a x)
a

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH5-2
...
c
ot
t1/2 =

∴

t1/2

unit of k is (conc)(n1) (time)1
...

1
n1

it

rs

LM
N
LM 2
1
=
k(n 1) N a

∴

n1

OP
Q
OP
Q

ni

For t1/2, x = a/2

1
1
1
n1
n1
t (n 1) ( a x)
a

lu

k=

ve

LM
N
LM 1
1
t=
k(n 1) N ( a x)

∴

gi

ca

Example 9
...
If the specific reaction rate is
5
...
2 × 103 mol1 litre min1

ch

Here,

te

5
...
For a 2nd order reaction

a=

a/2
1
=
60
...
a / 2 60a
1
= 3
...

60 × 5
...
When the initial concentration is changed from 0
...
to 25 sec
...

Sol
...
5 mol l1
a2 = 1 mol l1

n 1

2 = 2n1

or
∴
or

FG IJ
H K

50
1
=
0
...
blogspot
...
PM5

125

sp

125

REACTION DYNAMICS/CHEMICAL KINETICS

...

1
1
1
=
=
l mol1 sec1 =
...
5 × 50 25

t=

k
0
...

ak(a x) 0
...
2

it

y
...
In a 2nd order reaction, the initial concentration of reactants is 0
...

The reaction is found to be 20% complete in 40 minutes
...

a = 0
...
Here,

ni

x = 0
...
2 × 0
...
02 mol l1
t = 40 min
...
1 0
...
08 mol l1

x
0
...
1 × 40 × 0
...
0625 l mol1 min1
1
at1/2

no

k=
t1/2 =

ht
tp
:/
/k
er
al
a

te

ch

∴

∴

1
1
=
= 160 mins
...
1 × 0
...
75a = 0
...
0625 mol1
...
025 mol l1
t′ =

x′
0
...

ak(a x′ ) 0
...
0625 × 0
...
If one percent decomposes in the first minute in a unimolecular reaction,
calculate how much would remain undecomposed at the completion of the first hour
...
For a unimolecular reaction
k=

2
...
303
100
log
1
99
= 2
...
0044 min1
= 0
...
303
160
log
60
a x
2
...
01 =
60
ax
k=

or

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH5-2
...
c
ot
og

(a x) = Antilog 1
...
89
% undecomposed = 54
...

it

∴
∴

y
...
01
= log
= log 100 log (a x)
a x
2
...
2605
= 2 0
...
7395

or

ve

rs

Example 13
...
For nth order reaction,

ni

unit of k = mole1n ln1t1 when c = mol l1
mole1n ln1 t1 = mole1n 103(n1) mln1 t1 when c = mol ml1

lu

and

ca

For first order reaction,
k1 = t1 (k1 will remain same)

ht
tp
:/
/k
er
al
a

te

ch

no

lo

gi

For second order reaction,
k2 = mole1 lt1
k2 = mole1 103 ml t1
or
103 k2 = mole1 ml t1
For third order reaction,
k3 = mole2 l2 t1
= mole2 106 ml2 t1
or
106 k3 = mole2 ml2 t1
So, the reaction will be,
k1 = 103 k2 = 106 k3
...
A certain substance A is mixed with equal moles of a substance B
...
How much A and B will be left increased at the end of two
hours if the reaction is: (i) first order in A and independent of B, (ii) first order in A and first
order in B?
Sol
...

x = 0
...
303
a
a
log
= 2
...
75a
0
...
303 log 4 = 1
...

(i) When first order in

A=K=

when time t′ = 2 hrs
...
3865 =
log

∴

2
...
3865 × 2
=
= 1
...
303

(a x′) =

[where x′ = amount reacted]

a
= Antilog 1
...
5%
16
16

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH5-2
...
c
ot
og

ENGINEERING CHEMISTRY

So, % of A left unreacted = 12
...

t′ = 2 hrs
...
75a
=
= 3a1 hr1
at(a x) a × 1 × 0
...
r
...
B)
(ii) In the second case, the over all order of the reaction is 2
...
100 ≈ 14
...

7
Example 15
...
45 × 105 and 162 × 105
...

Sol
...
e
...
303R
T1T2

ch
ht
tp
:/
/k
er
al
a

Here,

te

log

T1 = 273 K

k2 = 162 × 105

OP
Q

T2 = 303 K k1 = 2
...
987 Cal K1
...
303 × 1
...
45 × 10
1
...
303 × 1
...

Example 16
...
6 kJ mol1, respectively for a first order reaction
...

Sol
...

As the reaction is first order, k =
Here,

0
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH5-2
...
c
ot
og

0
...
155 × 103 sec1
From Arrhenius equation we have,
2
...

Ea
2
...
mol1, R = 8
...
115 × 103 sec1
...
303 × 8
...
115 × 10 JK

ni

∴

rs

T=

3

lu

or

k=

it

∴

K

3

98600
K
2
...
316 × 16
...

Example 17
...
0 × 103 l mol1 s1 has an activation energy of 45 kJ mol1
...
We have,

no

lo

gi

ca

=

K2
E (T T1 )
= a 1
K 1 2
...
5 × 104 J mol1
T2 = (875 273) = 1148 K, T1 = (800 + 273) = 1073
R = 8
...
5 × 10 4 (1148 1073)
= 0
...
303 × 8
...
1431 = 1
...
39 × 5 × 103 l mol1 s1
= 7
...

Lasers in Chemistry
Laser means light amplification by stimulated emission of radiation
...

To achieve a laser action a Population inversion should be generated in the system
...
When
E2 > E1, let us state we have a population inversion with n2 > n1, then photons of frequency
1→2=

E 2 E1
are spontaneously emitted as molecules drop from the state 2 to the state 1
...
blogspot
...
PM5

129

sp

129

REACTION DYNAMICS/CHEMICAL KINETICS

...
5
...

3

it

y
...

2

ca

lu

ni

ve

rs

The laser system is contained in a cylindrical cavity whose
ends have parallel mirrors
...
Those
photons emitted at the cylindrical axes pass out of the system and
1
have no role in the laser action
...
5
...
States involved in
laser action
...
The presence of end mirrors makes the laser a
standing wave pattern
...
This makes the laser nearly
2
monochromatic, the laser output is highly monochromatic and highly directional
...
Thousands of different lasers
exist; the material in which the laser action can be employed may be a solid, a liquid or a gas
...

te

Solid-state metal ion laser
...

Gas laser
...

Dye laser
...
The HF chemical laser can be used as an antimissile
...
Then we can study the dependence of the reaction probability on
the vibrational quantum states of these reactants
...
Thus, laser light can be employed to control the outcome of the reaction
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH5-2
...
c
ot
og

sp

131

REACTION DYNAMICS/CHEMICAL KINETICS

bl

By using laser, one can preferentially break the O H bond in HOD, similarly, excitation
of O-D stretching vibration in HOD leads to break the OD bond preferentially
...

y
...
By using laser light, the bond breaking process can be observed
spectroscopically
...
The experiments are done using either molecular beams or
gaseous molecules in a chamber
...

lu

ni

SHORT QUESTIONS

ve

rs

it

10 12

ch

no

lo

gi

ca

Lasers in Chemistry:
Q
...
What is a laser?
Q
...
Explain why the laser radiation is monochromatic
...
3
...

Q
...
Give an example of chemical laser
...
5
...
6
...
7
...

te

SHORT QUESTIONS AND ANSWERS

ht
tp
:/
/k
er
al
a

Q
...
What do you mean by chemical kinetics?
Ans
...

Q
...
What do you mean by rate of a reaction?
Ans
...
The rate of reaction is increased if the
concentration of the reactants increases
...

∆A
∆B
Rate of reaction =
or +
∆t
∆t
Unit = Concentration time inverse
...
3
...
It is the rate of the reaction when the concentration of the reactants are unity
...
4
...
(1) Temperature, (2) Order of a reaction
...
5
...

Ans
...
blogspot
...
PM5

131

...
The average rate approaches the instantaneous rate when ∆t becomes smaller
...

Q
...
What do you mean by the order of a reaction?

it

Ans
...
If we take a
reaction:

...
Cγ

ve

the rate = k
...

ni

Q
...
What is the molecularity of a reaction?

lu

Ans
...
e
...
If the reaction is:

ca

C12H22O11 + H2O → C6H12O6 + C6H12O6

gi

The molecularity of the above reaction is two
...

lo

Q
...
What are unimolecular and bimolecular reactions?

no

Ans
...

te

Order

ch

Q
...
Compare order and molecularity of a reaction
...

ht
tp
:/
/k
er
al
a

(i) Order is a purely experimental fact related to
the rate equation of the reactions
...

(ii) If a reaction is

A + B → Products

the rate will be

Rate = K
...

Molecularity
(i) Molecularity is a theoretical concept
...
In modern
definition it is related to the mechanism of
the reactions
...

Modern definition isit is the number of
molecules taking part in the rate
determining step of the mechanism
...

(iii) Molecularity does not depend on such
factors
...

(iv) Molecularity is always a whole number
...
For complex reactions
it may or may not be equal
...
blogspot
...
PM5

132

...
10
...

rs

it

dA
= k
...

dt

y
...
If the rate of a chemical reaction varies to the first power of concentration of the
single reactant, it is known as first order reaction
...
11
...

ve

Ans
...
Radioactive disintegration process
...
12
...
Rate of growth of bacterial culture
...
A second order reaction is a reaction, the rate of which is directly proportional to
the square of the concentration of a single reactant or equal to concentration of two different
reactants
...
[A] [B]

or Rate = k
...

lo

Q
...
Comment on half-life of a first order and a second order reaction
...
t1/2 for a first order reaction =

0
...
So, it is a constant quantity
...

ak

te

t1/ 2 for a second order reaction =

So, half-life in this case is inversely proportional to the initial concentration
...
14
...
Integrated form for a first order rate equation is:
c = c0ekt

The plot of concentration vs
...
Hence, concentration will be
zero at infinite time
...

For a second order reaction the integrated form of the rate equation is:
k=

when,

x
1
t a(a x)

x = a, t = ∞

So, a second order reaction is also an incomplete reaction
...
15
...
What is the time for the change from c/2 to c/4?
Ans
...

Q
...
For a second order reaction one hour is needed for a change of
concentration a to a/2
...
blogspot
...
PM5

133

sp

133

REACTION DYNAMICS/CHEMICAL KINETICS

...

t1/ 2
′
1
=
′
t1/ 2 ak

1
a/ 2
...
t1/2 = 2
...

′

it

When concentration changes from a/2 to a/4, t1/2 =

1

...
When concentration changes from a to a/2, t1/2 =

og

ENGINEERING CHEMISTRY

ve

rs

Q
...
What is the special characteristic of a zero order reaction?
Ans
...

ni

K=

c0
ka
which is a finite quantity
...

Q
...
What is activation energy?
Ans
...
It is denoted by EA
...
19
...
It is the minimum amount of energy from zero level of the reactant molecule which
must possess in order to react
...

Q
...
How are the activation and threshold energies related?
Ans
...
21
...
Chemical reactions occur through an intermediate stage known as transition state
or activated complex (Fig
...
6)
...
5
...
blogspot
...
PM5

134

sp

134

...

y
...
22
...
The study of chemical kinetics helps to determine the mechanism of a chemical
reaction
...

7
...

9
...

5
...

Explain the terms rate constant, order of a reaction and molecularity of a reaction
...

Indicate how the specific reaction rate of a first order reaction can be evaluated
...

Discuss any two methods of determination of order
...

Discuss the various factors affecting the rate of a reaction
...

Describe an accurate method for determining order of a reaction with three reactants
...
Derive the rate constant expression of a 2nd order reaction:

ch

1
...

ni

EXERCISES

k

te

A + B → c, the reactants A and B are at equal concentrations
...
How does rate of a reaction vary with temperature? What is Arrhenius equation?
11
...

State the molecularity and order of the above reaction
...
Briefly develop the concept of activation energy and temperature
...
Classify the statement: decomposition of H2O2 is of the 1st order
...
Half-time change for a 1st order reaction is 40 mins
...
0173 min1]
15
...
Calculate the rate constant and the time
taken to complete 80% of the reaction
...
85 mins]
16
...
From the given data, show that
the reaction is of the 2nd order
...
During the hydrolysis of ethyl acetate by NaOH using equivalent concentration, 25 c
...
of the
reaction mixture was titrated at regular intervals against standard acid
...
of acid (c
...
)

16

10
...
13

4
...
41

Show that the reaction is of the 2nd order
...
blogspot
...
PM5

135

...

3
...
92

bl

18
...

Find the reaction is of which order
...
0

10
...
13

4
...
41

ca

Show that reaction is of 2nd order
...
The decomposition of Cl2O7 at 400 K in the gas-phase to Cl2 and O2 is a 1st order reaction
...
062 to 0
...
Calculate the
rate constant
...
of decomposition at this temperature
...
6
...
0332 atm]
20
...
How long will it take to go
to 60% completion?
[Ans
...
The following data were obtained in the hydrolysis of ethyl acetate, using equal concentration of
ester and NaOH:
Time (minutes):
0
5
15
25
35
Vol
...
c
...
A 1st order reaction has rate constant equal to 1
...
5 × 104 sec1 at
318 K
...

[Ans
...
Two reactions:
(i) A → Products, (ii) B → Products, follow first order kinetics
...
The half-life for this reaction at
310 K is 30 minutes
...
If the energy
of activation for the reaction (ii) is half that of reaction (i), calculate the rate of the reaction
(ii) at 300 K
...
0
...
The activation energy for the reaction
mol1

2HI (g)

H2 (g) + I2 (g)

ht
tp
:/
/k
er
al
a

is 209
...
Calculate the fraction of molecules of reactants having energy equal
to or greater than activation energy
...
1
...
When log K (velocity constant for a reaction) was plotted against 1/t, the slope of the line was
found to be 5400 K
...
314 JK1 mol1)
[Ans
...
4 kJ mol1]

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH5-2
...
c
ot
sp
og
bl
y
...
Berzelius named the phenomenon of acceleration of the reaction
as catalysis and the substance influencing the reaction, a catalyst
...

gi

DEFINITION

ht
tp
:/
/k
er
al
a

te

ch

no

lo

A catalyst is a substance, not related to the reactants, influences the velocity of the
reaction by not involving itself in the reaction
...

A catalyst may also retard a chemical reaction
...

(i) Positive catalysis or catalysis
...

(ii) Negative catalysis
...

Examples of Catalysis
Positive Catalysis

(i)
(ii)

(iii)
(iv)

Reaction

Catalyst

2KClO3 → 2KCl + 3O2
2H2O2 → 2H2O + O2

2SO2 + O2 → 2SO3
N2 + 3H2 → 2NH3

(v) C12H22O11 + H2O → C6H12O6 + C6H12O6

MnO2
Pt
Pt or V2O5
Fe
H+ ion

Negative Catalysis
Reaction

Catalyst

(i)
2H2O2 → 2H2O + O2
(ii) 2H2 + O2 → 2H2O

H2SO4
CO
137

http://keralatechnologicaluniversity
...
com

...

bl

A small amount is effective
...

Catalyst hastens the attainment of equilibrium
...

Catalytic action is universal
...
So it has no influence on
the standard free energy change ∆G° i
...
, on K, the equilibrium constant of the
reaction as the two are related by ∆G° = RT ln K
...

• Catalyst only helps to attain the equilibrium rapidly
...

• So a catalyst is a substance that makes a chemical reaction that could happen,
but does not happen, happen
...

• This means if a catalyst accelerates the forward reaction, it also accelerates the
backward reaction, it never increases the equilibrium yield
...
Those catalysts are termed
Enzymes or Low catalysts
...

This type of catalytic reactions occur in gas or solution phase i
...
, in one single phase
...
blogspot
...
PM5

138

sp

138

...

bl

In this type of catalytic reactions, the catalyst forms a separate phase, usually a finely
divided solid either as such or supported on an inert solid such as asbestos or gas (fluidised
bed)
...
This type of catalysis has a great technical
importance
...

Schematically it is represented as follows:

Catalysed
reaction

Reactants
Products
Progress of reaction

Fig
...
1 Progress of reaction
...
Catalyst lowers the energy of activation (Ea) of a reaction
...
)

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH6-1
...
c
ot
(ix) Halogenation
(x) Polymerisation

bl

y
...
If we take water and a non-aqueous solvent like benzene and if the
reactants remain in the benzene phase and the catalyst in the water phase the reaction is
accomplished at the interface provided a little surface active agent (detergent) is added to the
system
...

Highlights:

ht
tp
:/
/k
er
al
a

te

ch

no

lo

Two other types of catalytic reactions are to be noted
...

(b) Decolourisation of KMnO4 by oxalic acid
...

(ii) Induced catalysisSodium arsenite solution is not generally oxidised by O2
but sodium sulphite is oxidised
...
This type of catalytic
reaction is known as induced catalytic reaction
...
These substances
are called catalyst poisons or anti-catalysts
...
The poison acts very likely by blocking the active sites
of the catalyst
...
An important catalyst promoter is Al2O3 and alkali metal oxide,
when used with iron in the Habers process, the catalytic action increases
...

(ii) Always a small quantity of catalyst is required
...

(Contd
...
blogspot
...
PM5

140

sp

140

...
6
...

no

(vii) Change of temperature can alter the rate of a catalytic reaction as for a noncatalytic reaction
...

(i) Intermediate compound formation theory
This theory explains the catalytic reaction due to the formation of an unstable
intermediate compound which is more reactive compared to the reactants
...

2NO + O2 = 2NO2
...
H2SO4 to ether
...

δ+

δ−

RCl + AlCl3 → R
...

(ii) Adsorption theory (Heterogeneous catalysis)
This theory mainly explains the mechanism of a catalytic reaction between two gases
catalysed by a solid
...

The adsorption theory is compared to the intermediate compound formation theory
...
blogspot
...
PM5

141

sp

ot
C+D

rs

Reaction: A + B

A+B

it

y
...

(v) A catalyst cannot initiate a reaction
...

og

141

CATALYST

...

ca

H
Ni

Ni

H

C

gi

H

Ni

(b) HH bond weakened and broken
by chemisorption

H
C

Ni

ve

H

Ni

y
...
The
adsorption theory can be explained by the following Fig
...
3
...

lo

Fig
...
3 (a), (b), (c) and (d)
...
These reactions are catalysed by certain organic compounds
which are known as biocatalysts or enzymes
...
But not all protein molecules are enzymes
...
The protein molecules, which do not contain those active sites cannot function
as enzymes
...
The following
figure explains the enzymatic activity:
Enzymatic activity can be explained as:
Enzyme + Substrate
Enzyme Substrate → Products + Enzyme
[activated complex]

The reaction is abbreviated as:
E+S
E S → P + E
...

The reaction may be represented pictorially as follows (Fig
...
4)
...
6
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH6-1
...
c
ot
og

Examples of enzymatic reactions

bl

(i) Inversion of cane sugar
Invertase

glucose

y
...

2 2

(iv)

lu

Highlights:

ni

(iii)

ca

• Enzymatic reactions generally take place at 35°-45°C
...

gi

• Enzymes do not act in cold conditions
...

no

• For its full activity, enzyme needs help of another factor (compound) known as
co-factor or co-enzyme
...

ht
tp
:/
/k
er
al
a

te

ch

• Enzymatic reactions not at all depend on the concentration of the reactant i
...
,
substrate i
...
, enzymatic reactions are zero order reactions
...
1
...
A catalyst is a substance that speeds up chemical reactions without changing itself
...
2
...
A catalyst cannot change the free energy change of a reaction
...
3
...
A catalyst does not alter the equilibrium constant of a reaction, it only shortens
the time of attaining the equilibrium
...
4
...

Ans
...

Q
...
Draw a distribution curve showing how the proportion of molecules able
to react increases when a catalyst lowers the activation energy
...
blogspot
...
PM5

143

sp

143

CATALYST

...

Number of molecules
with kinetic energy (E)

Activation energy
with a catalyst

Fig
...
5

ni

Kinetic energy (E)

lu

Give experimental evidence that different catalyst has no influence on the
yield of a reaction
...
It has been observed that at the same temperature the yield of SO3 is the same,
whether the catalyst used be Pt, Fe2O3 or V2O5
...
6
...

no

lo

Ans
...
Aromatic amines,
thiourea, etc
...
Widest technical use
of negative catalyst is TEL as antiknock compound in motor fuel
...

ch

Q
...
What is autocatalysis?

te

Ans
...

Completion of reaction

Rate of reaction

ht
tp
:/
/k
er
al
a

Q
...
Draw a graph for an autocatalytic reaction
...
6
...
In autocatalysis reaction as the catalytic product is gradually formed, the rate of
reaction increases
...
6
...

Q
...
Why is the hydrolysis of ethyl acetate autocatalytic?
Ans
...

CH3COOC2H5 + H2O → CH 3COOH + C2H5OH
catalyst

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH6-1
...
c
ot
og

sp

145

CATALYST

ca

lu

ni

ve

rs

it

y
...
10
...

Ans
...

If the catalyst is in a different phase, it is a heterogeneous catalyst
...

(ii) Heterogeneous catalyst (contact catalyst) = In Habers process for manufacture of
ammonia (Fe + Al2O3 + K2O)
...
11
...
Enzymes are proteins in nature and are the catalysts for biochemical reactions
...
12
...
Some washing powders contain proteasesenzymes that remove blood stains on
dirty clothes
...
13
...

Ans
...
Each enzyme catalyses a particular reaction
...
Each
enzyme works best at a particular temperature and pH
...
A
...
)

gi

CATALYTIC APPLICATIONS OF ORGANOMETALLIC COMPLEXES

ch

no

lo

To explain the formation of a complex of a metal with a ligand, it was suggested by
Sidgwick that metal ions will tend to accept the electron pairs from donors, i
...
, ligand until
they have obtained a sufficient number of electrons, so that a metal ion in the resulting complex
has an effective atomic number of the nearest inert gas
...

ht
tp
:/
/k
er
al
a

te

So, the effective atomic number (E
...
N
...
e
...
The rule can be
exemplified by the following table:
E
...
N
...

of metal

Co-ordination
number

Electrons
lost in ion
formation

Electrons
added by
co-ordination

E
...
N
...
e
...
The statement of 18-electron rule is that the valence
shell of metal atom will attain 18 electrons by saturation of (n 1) d, ns and np orbitals of
metals by the ligands
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH6-1
...
c
ot
og

ENGINEERING CHEMISTRY

No
...
of
electrons in
(n 1) d, ns
and np levels

y
...

Structure and bonding in organometallic complexes, the 16-and 18-electrons rule:

lo

The role of metals in catalytic cycles during some chemical reactions:

no

• Hydrogenation using (Ph3P)3RhCl

ht
tp
:/
/k
er
al
a

te

ch

The hydrogenation of unsaturated organic compounds i
...
, mostly alkenes is an important
industrial reaction
...
Homogeneous systems are used for pharmaceutical
industries
...
The hydrogenations of
alkenes and alkynes have been studied extensively
...
The catalyst is not able to reduce other organic functional groups, though it is a very
reactive compound
...

The action of the Willkinsons catalyst is represented by the following cycle
...
The 14-electron species (II) is formed by
dissociation of phosphene ligand from (I)
...
This is because stable Rh(I) complexes are generally four
coordinated (16-electron species)
...
The stage IV is very very significant in the overall hydrogenation
process as in this stage, the substrates alkene, hydrogen are now bonded to the same metal
atom
...
(V) undergoes reductive
elimination to release the alkane and regenerate the 14-electron species
...
blogspot
...
PM5

146

sp

146

...
6
...

ht
tp
:/
/k
er
al
a

te

H

H

Rh

ch

no

16e
(V)

lo

L

Cl

L

ca

lu

ni

ve

H H

14e
(II)

rs

Cl

it

Rh
C—C

y
...

• Reductive elimination refers to the decrease in coordination site of the central metal
...
e
...
The reaction,
which takes place in presence of a catalyst is as follows:
Catalyst

R
...
But among
them, catalysis by cobalt or rhodium compounds is of interest
...
As this needs high pressure
reactor the initial installation cost of the plant is high for an industrial process
...
blogspot
...
PM5

147

sp

147

CATALYST

...

it

y
...

3
...

5
...

7
...

9
...
6
...

RCH2CH2Co(CO)3

RCH2CH2Co(CO)4

no

O

lo

RCH2CH2CCo(CO)3

Insertion of
alkene into
Co—H

EXERCISES

Define with illustrations:
(i) catalysis,
(ii) positive catalysis,
(iii) negative catalysis
...

A catalyst doesnt affect the final state of equilibrium, although it shortens the time required to
establish the equilibrium
...

Give a brief account of the various theories of the mechanism of catalysis
...

How does a catalyst accelerate the speed of a reaction? Explain with proper energy profile diagram
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH6-1
...
c
ot
og

sp

149

CATALYST

ht
tp
:/
/k
er
al
a

te

ch

no

lo

gi

ca

lu

ni

ve

rs

it

y
...
Give one example of an industrially important catalytic reaction, mentioning the specific catalyst
used
...
Write an account of the kinetics of heterogeneous catalytic reaction
...
Write notes on:
(i) Catalyst and equilibrium point
...

(iii) Phase transfer catalysis
...
Write briefly on acid-base catalysis
...
What are the chief criteria of catalysis? Describe four applications of catalysis
...
Write notes on:
(i) Hydrogenation catalysts and oxidation catalysts and their application in India
...

16
...

17
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH6-1
...
c
ot
sp
og
bl
y
...
Addition

3
...
Substitution

ca

Organic reactions

4
...
One
covalent bond is made of a pair of electrons
...
e
...
If the bond is
between two atoms of unequal electronegativities, then the influence of the atoms on the bond
is not the same
...
The displacement
of the bonding electrons will be towards the atom of greater electronegativity
...
For example, in methyl
chloride, the bond between carbon and chlorine is polarised and the bonding electron is displaced
towards chlorine atom as follows:
–

Inductive Effect

As a result of the displacement of the bonding electrons between CCl, carbon atom
acquires a small positive charge and the chlorine atom acquires a small negative charge
...
And this effect is permanent
...

This inductive effect has a great influence on the character of organic compounds as
well as on organic reactions
...

This phenomenon is explained as follows: Due to inductive effect of chlorine atom the release
of proton from chloroacetic acid (Ka = 1
...
85 × 105)
...
blogspot
...
c
ot
The electronegativity scale is represented as follows:

og
bl

rs

NO2 > F > COOH > Cl > Br > I > OH > OCH3

y
...
Due to (+I) effect of CH3
group, CH3COOH is weaker acid than HCOOH
...
It is an example
of (+I) effect
...
If an organic molecule contains a double
bond, then the π electrons are transferred completely to one of the bonded atoms under the
influence of attacking reagents
...

HA +

A

H

C ¾C

The effect is generally represented by a bend arrow
...
This sort of polarisation
effect is the cause of many organic reactions
...
The bond break-up may be homolytic or heterolytic
...
H

(b) heterolytic
bond breaking

C
...
Free radicals are generated due to homolytic fission and carbocations and
carbanions are generated due to heterolytic fission of the bond
...

When the reaction takes place through free radical formation (Fig
...
blogspot
...
PM5

151

sp

151

MECHANISM OF ORGANIC REACTIONS

...
When the reaction takes place through the
formation of an ion (Figs
...

y
...

...

CH 3 + Cl 2 → CH 3Cl + Cl

...

Cl + Cl → Cl 2

...

CH 3 + CH 3 → CH 3

it

The chlorination of methane, i
...
, substitution of methane takes place through free radical
mechanism
...
It is represented as follows:

C

+ (RCO2)2

gi

C

ca

Polymerisation reactions also take place through free radical mechanism
...

C
n

...

(RCO2)2 → 2R CO2 → 2 R + 2CO2

lo

(i) Initiation:

te

ch

no

 



...

C + nC

C

R

C

C

C

C

...

...

Classification of Reagents
The reagents which take part in ionic reactions are categorised as:
1
...
Nucleophiles or nucleophilic reagents
Electrophiles mean electron seeking, i
...
, these reagents attack at the point of highest
electron density of a molecule
...
On
the contrary, nucleophiles mean nucleus seeking, i
...
, they attack at the positive centre of a
polarised molecule
...

Nucleophiles
Electrophiles
(a) OH, CN, Cl, Br, I
(b) Double and triple bonds of alkenes
and alkynes
...

(b) Halogen and halogen acids
...
blogspot
...
PM5

152

...

bl

(c) Compounds containing an atom with
(c) H2SO4, HNO3, HNO2, etc
...

(d) R2O:, :NH3 , R3N:, etc
...

That means electrophiles are Lewis acids i
...
, electron pair acceptors and nucleophiles
are Lewis bases i
...
, electron pair donors
...
Conventionally, if the attacking reagent be an
electrophile, the reaction is called electrophilic reaction and when the attacking reagent is
a nucleophile, the reaction is called nucleophilic reaction
...
Electrophilic reactions
2
...
addition and substitution
...

Another type of reaction is very common in organic chemistry which is known as
elimination reaction
...
If we
take chlorination of methane for example
...
The minimum amount of energy that must be provided by a collision for reaction to
occur is called the energy of activation (Eact)
...
The potential energy at any stage of the reaction is indicated by the height
of the curve (see Fig
...
1)
...

DH = 1 Kcal

...

Reaction: CH4 + Cl ¾® CH3 + HCl

...
7
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH7-1
...
c
ot
og

ENGINEERING CHEMISTRY

Examples:

y
...
Electrophilic addition
...
The positive bromine ion then gets attached to a carbon atom attached to a
double bond making other carbon atom of the double bond a carbocation, that carbocation gets
attached to the Br generated
...
S
...
S1

Potential energy

ht
tp
:/
/k
er
al
a

te

2
...
Electrophilic substitution takes place in three steps
...

Step 1
...
Formation of a transition state:

T
...
S
...
H + NO2
Ar
...
blogspot
...
PM5

154

...

H

bl

Setp 3
...

(+)

it

+ H2SO4

rs

Here after the attack of the electrophile the stable aromatic system is disturbed
...

R
R

d+

C

R

d+

C

R

d–

O

d–

R

d+

d–

lu

R

R

O

O

ca

C

(–)

C

O

R

+

CN

+H

R

gi

(b)

R

ni

ve

3
...
Addition of HCN to a ketone is an example of nucleophilic
addition
...
The carbonyl group of the ketone polarises HCN and the addition takes place as
follows:
(a)

C

OH
CN

ch

no

lo

CN H
4
...
Nucleophilic attack on the carbon atom of CX bond in
a haloalkane or alkyl halide, RX, leads to substitution, where X = Cl, Br or I
...
Study of the rate equations of the
reactions suggests that there are two different mechanisms:

(a) Nucleophilic substitution unimolecular (SN1)

te

(b) Nucleophilic substitution bimolecular (SN2)
...
This is a two-step process
...
Ionisation of the alkyl halides i
...
, formation of a carbocation intermediate by
breaking of CCl bond
...

CH3
CH3

C

Slow

Cl

CH3

H 3C
H3C

+

C + Cl

–

H3C

Tertiary butyl carbocation

Tertiary butyl carbocation is stable due to the (+I) effect of the methyl groups
...
e
...

H3C
H 3C

Step 2
...
Here the rate equation is
rate = K [alkyl halide]
...
blogspot
...
PM5

155

sp

155

MECHANISM OF ORGANIC REACTIONS

...

C

it

–

bl

The mechanism of the substitution can be represented as follows:

OH +

T
...

rs

Here the mechanism shows that CX bond breaks as the nucleophile OH forms a new
bond with carbon simultaneously
...

ni

ve

Elimination reaction
...

Br

C

C

+ KBr + H2O

ca

H
Elimination of a hydrogen halide from an alkyl halide produces alkene
...

no

(a) E1 reaction
...

ch

X

ht
tp
:/
/k
er
al
a

H

Step 2
...
This reaction occurs in one step process
X
C

C

–

X +

C

C

+ H:B

H :B

Another example of elimination reaction is the removal of water from an alcohol to form
an alkene
...
H 2SO 4
H  C  C  C  H → H  C C  C  H
Heat ( H 2O)
  
  
H H H
H H H

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH7-1
...
c
ot
C

H

H

H

H

H C

C

C

H

¾¾¾®

H

H

H

¾¾¾®

H C
H

og
H
+

C

C

H

H

¾¾¾®

H C

C

C

H

H

H

H

lu

Resonance

H

H

ni

ve

y
...
Thus
H

ca

The idea of resonance has a major role in understanding the mechanisms of reactions
...

(II)

no

(I)

The structures (I) and (II) cannot satisfactorily explain all the properties of benzene
...
Despite having three double bonds benzene undergoes substitution reactions more
easily than addition reactions
...
Benzene is more stable than expected
...
All the CC bond lengths in benzene is 1
...
54 Å for a single bond and
1
...

The Kekule structure is still the accepted structure for benzene
...
That theory is the concept of resonance
...
The primary
conditions for drawing the resonating structures are:
(a) Position of atoms in the molecule cannot be changed and the molecule should be
planar
...

(c) Only π electrons and non-bonded electrons can be shifted
...
Each of these drawn structures contributes to the resonance hybrid (Fig
...
2)
...
The
difference in energy of any of the contributing structures and the hybrid structure is called the
resonance energy (Fig
...
2)
...
blogspot
...
PM5

157

sp

157

MECHANISM OF ORGANIC REACTIONS

...

it

(Resonating structures)

Benzene + 3H2

(Resonance hybrid structure)

Cyclohexene + H2
28
...
4 Kcal 57
...
8 Kcal
(obs) 85
...

Sign of resonance
Cyclohexatriene + 3H2

ca

Cyclohexane

Fig
...
2 Stability of benzene (Resonance energy)
...
e
...
8 Kcal/mol but actually it is 49
...
That is, benzene is
more stable by 36 Kcal/mole than expected which is resonance energy of benzene
...

ht
tp
:/
/k
er
al
a

te

(iii) As a resonance hybrid benzene is more stable than either of the contributing resonating structures i
...
, Kekule structures, this additional stability possessed by benzene
is responsible for substitution reactions of benzene and for a new set of properties
called aromatic properties or aromaticity
...
For this overlapping, the three electrones i
...
, the odd electron and
the bond pair of the CH bond, help to bind together the three nuclei i
...
, two carbons and one
hydrogen
...

In terms of resonance, the hyperconjugation may be represented as follows:

...
←→ H C C ←→ H  C C ←→ H  C C
 
 





...
But it is apparent that
the CH bond is something less than a single bond and the odd electron is partly accommodated
by the H atoms
...
Victor
Meyer attempted to explain these abnormalities by steric hindrance i
...
, ogroups in 2, 4,

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH7-1
...
c
ot
og

sp

159

MECHANISM OF ORGANIC REACTIONS

NH = CH

y
...
e
...

it

Anil

NH2 + OCH

Br

NO reaction

ve

Br

rs

Br

C

Nu

X

gi

...
When a
chemical reaction occurs, it does so via transition state
...

In an SN2 reaction:

C

X

Nu

–

C+X

Crowded transition state (T
...
)

ch

no

lo

The transition state accommodates more atoms than the initial state
...
S
...
From the foregoing discussion we can say, SN1 reactions will not be affected by the
influence of steric hindrance whereas SN2 reactions are very much affected by steric hindrance
...
CH2
...
CH2
...
CH3

(Rearrangement)

H

Primary (1°) carbocation

Tertiary (3°) carbocation

This type rearrangement takes place by migration of a hydrogen atom with a pair of
electrons known as a hydride shift or an alkyl group with a pair of electrons known as alkyl
shift or 1, 2-shift
...
This shift is very much important in understanding
organic reactions
...

H

+

C

C

Å

C

C

C

...

R

(An alkyl shift)

Å

H
+

C

...
blogspot
...
PM5

159

...

bl

Different organic compounds having the same molecular formula are known as isomers
...

The isomerism is of two types:

it

(i) Structural isomerism
(ii) Stereoisomerism
...

Molecular formula
(i) Butane [C4H10]

Different structures (Compounds)

(i) CH3 CH 2 CH 2  CH 3 (ii) CH 3  CH  CH 3
n-butane

CH 3

lo

gi

(a) Chain isomerism

ca

Types of isomerism

lu

Examples are displayed in the following table
...
CH2
...
CH 2
...
Cl
1-chloropropane

(ii) CH3 CH CH3

Cl
2-chloropropane

(Contd
...
blogspot
...
PM5

160

...

(iii) C6H9(OH)2

meta- OH

ortho-

og

OH

OH

bl

OH

OH

(iii) CH
3

O

rs

(ii) CH 3OC3H7
methyl
n-propyl ether

ve

(i) C2H5OC2H5
diethyl ether

CH

ni

(i) C4H10O

it

para-

(d) Metamerism
(isomerism in the
same class of organic compounds)

CH3
CH3

lu

Methyl isopropyl ether

gi

ca

Bond rotation (Fig
...
3) is possible about single covalent bonds but is prevented under
normal conditions by double bonds or triple bonds
...
The topic has been treated later on
...
7
...

Conformational Isomerism

ht
tp
:/
/k
er
al
a

The different spatial arrangements arising out of the rotation of a CC single bond are
known as conformations
...
The two conformers of ethane are given in Fig
...
4(a)
...
7
...

There are many other conformers between these two extremes
...
The rotation about C2C3 bond of n-butane gives different conformers as
depicted in Fig
...
4(b)
...
blogspot
...
PM5

161

sp

161

MECHANISM OF ORGANIC REACTIONS

...

bl

og

ENGINEERING CHEMISTRY

sp

162

4
...
1 Kcal

rs

Potential energy

3
...
9 Kcal

Gauche

Eclipsed

Gauche

gi

Angle of rotation

lo

Fig
...
4 (b) Potential energy changes during rotation about C2C3 bond of n-butane
...
In two Gauche conformations, the
CH3-groups are 60° apart and they are less stable than the anti-form and more stable than
the eclipsed form, the eclipsed conformation is least stable due to severe crowding
...
e
...

• Any deviations from the normal, i
...
, sp3 hybridised carbon (bond angle 109
...

• Any pair of tetrahedral carbon attached to each other tend to have their bonds staggered
(i
...
, ethane-like)
...

• Any two atoms or groups that are not bonded to each other can interact
...
And the result can be either
destabilisation or stabilisation of the conformation
...
7
...

HA

HA

Chair
Conformer

HA
HB

HB

Twist
Conformer

HB

Boat
Conformer

Fig
...
4 (c) Conformers of cyclohexane
...
blogspot
...
PM5

162

...

bl

Newman projection formula of chair conformer [Fig
...
4(d)]:

ve

Fig
...
4 (d ) Cyclohexane (chair form) staggered form of ethane
...
So
the chair cyclohexane is more stable conformer of the cyclohexanes
...
7
...

Eclipsed ethane

Fig
...
4 (e)

ch

no

Cyclohexane (boat form)

ht
tp
:/
/k
er
al
a

te

The boat conformation is less stable than the chair conformation at an energy maximum,
it is thus not a conformer but a transition state between two conformers
...

The twist form or skew boat form is a conformer lying at energy minimum
...
The
half chair form is a most unstable form which lies at energy maximum (see Fig
...
5)
...
3 Kcal

11 Kcal
5
...
7
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH7-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

164

Stereoisomerism

lo

gi

ca

lu

ni

ve

rs

it

y
...
This part of
the science, which deals with structures in three dimensions is called stereochemistry
...

Since conformational isomers differ from each other only in this way, that their atoms are
oriented is space, they also belong to the stereoisomers
...
Optical isomerism is shown by the compound containing at least
one chiral carbon atom (asymmetric)
...
Generally,
a chiral carbon atom is one that is attached to four different atoms or groups
...
7
...
Polarized light is a light beam in which all the waves are vibrating in the
same plane
...
7
...

ht
tp
:/
/k
er
al
a

Light is plane-polarized after passing through a sheet of Polaroid
...
7
...

Mirror
COOH

H

COOH

OH

HO

CH3

H

CH3

Fig
...
7 Two configurations of lactic acid
...
7
...
Asymmetric molecules are chiral and can exist in distinct mirror image forms,
giving rise to optical isomerism
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH7-1
...
c
ot
og

C
OH

CH3

H3C

CO2H

HO

rs

HO2C

y
...
7
...

Asymmetric Molecules

lu

ni

If we translate the three-dimensional molecule to a two-dimensional figure, we get
Fischer projection formula of the molecule
...
7
...
If we rotate Fischer projection formula of one
molecule on the plane of the paper by 180° none of the configurations arrived at which is
superimpossible on the other
...
7
...
The two configurations of lactic acid rotate plane of polarised light in the
same degrees but in the opposite directions
...

Highlights:

• Number of possible stereoisomers = 2n
...

• A mixture of equal parts of enantiomers is called racemic modification
...
They can be separated by various
physical and chemical methods
...

CH3

CH3

CH3

CH3

H

Cl

Cl

H

H

Cl

Cl

H

Cl

H

H

Cl

H

Cl

Cl

H

C2H5

C2H5

(I)

(II)

C2H5
(III)

Fig
...
8 (c) Stereoisomers of 2, 3-Dichloropentane
...
blogspot
...
PM5

165

sp

165

MECHANISM OF ORGANIC REACTIONS

C2H5
(IV)

...

y
...
7
...

H

Cl

rs

Cl

ve

H

it

CH3

CH3

ni

Fig
...
8 (d) Optically inactive isomer (meso form)
...
This type of isomer is known
as mesoform
...
When similar
groups are attached to the same side of the molecule, the configuration is known as
cis-isomers (Z-isomers)
...
The geometrical isomerism
is also a case of diastereoisomerism [Fig
...
8(e)]
...
7
...
The system is often termed as absolute
configuration assignment as this type of specifying configuration is independent of any reference
compound
...
These are as follows:
• The number of stereocentres in the molecule are identified
...
based on sequence rule, such that 1 → 2
→ 3 → 4 or a → b → c → d
...

If the path provides a clockwise motion, then the stereocentre is designated to have R
configuration
...
7
...

The (R) or (S) designation is written in italics within the parentheses followed by a
hyphen before the name of the compound
...
blogspot
...
PM5

166

...

3

2

C

it

4

C

rs

4

1

bl

1

4

C

2

ni

C

3

lu

3

ca

1 ® 2 ® 3 anticlockwise
(S)–Configuration

2

1 ® 2 ® 3 clockwise
(R)–Configuration

gi

Fig
...
9 Assigning R and S notations
...
For
example, in 1-bromo-1-chloroethane (CH3CHClBr), the chiral centre is attached to CH3,
Cl, Br, H
...

ht
tp
:/
/k
er
al
a

te

• When the preferences cannot be determined on the basis of the atomic number of the
atoms directly attached to the chiral carbon, in this case, the atomic numbers of next
sets of atoms in the unassigned groups are taken into consideration
...
As for example, with 2-chlorobutane
(CH3CHClC2H5), the four ligands attached to the central chiral centre are CH3, C2H5,
Cl, H
...
For deciding the preference
between CH3 and CH2CH3 decision cannot be made on the basis of first Catom of
each group attached directly to the chiral centre
...
e
...
e
...

CH3

So, CH2CH3 gets priority over CH3
...

Similarly, in the case of CH2NH2 and CH2CH3 , the former will get priority over the

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH7-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

168

C ≡ X

equals

C

it

y
...

For example

lu

ni



But one thing to be kept in memory is that a real  C  A has priority over C ==A
...
The
complete priority sequence is then OH → CHO → CH2OH → H
...
The priority sequence of 1-amino-2-methyl-

HC C CH
1-phenyl-propane is NH2 → C6H5 → C3H7 → H
...
blogspot
...
PM5

168

...

bl

Example: (i) 3-chloro-1-pentene
...
For Fischer projection formula, the number 1 carbon should be on the top of
the vertical line
...

rs

• Then the asymmetric carbon atoms are to be determined
...

ve

• Then configuration is specified if priority sequence is a → b → c → d is clockwise and
hydrogen (d) remains in the horizontal line, then the configuration of the asymmetric
carbon atom is assigned to be S
...
e
...
Fischer projection of 3-chloro-1-pentene is:

Cl

CH = CH2

(d)

gi

*

H3C5¾C4H2¾CH¾H2C

(b)

(a)

H

CH2

3-Chloro-1-pentene

Cl

lo

CH2CH3

(c)

no

Fischer projection formula

ch

Priority sequence is: Cl→ CH = CH2 → CH2CH3

te

Rotation is anticlockwise and hydrogen is on the horizontal line
...

ht
tp
:/
/k
er
al
a

*
(ii) Alanine C3H3C2 H(NH2) COOH
...
Its optical isomer i
...
, enantiomer will inevitably be L-configuration, i
...
,
hydrogen will fall on the right hand side of the horizontal line
...
So
configuration is R
...
The configuration of the asymmetric carbon is S
...
blogspot
...
PM5

169

...

CH3

bl

(iii) For 2, 3-dichloro butane [C4H3C3
*H(Cl)
...
C1H3] the Fischer projection is

ni

(I) and (II) are enantiomers
...
(III) and (IV) are
known as mesoforms
...

ca

lu

In the case of (I) the priority sequence for carbon number (2) is Cl → CH(Cl)CH3 → CH3
...

The priority sequence for carbon number 3 is Cl → CH(Cl)CH3 → CH3
...

So the IUPAC nomenclature of the compound (I) is:

lo

(2S,3S)-2,3-Dichlorobutane
...

no

E and Z Nomenclature

ht
tp
:/
/k
er
al
a

te

ch

For the compounds of the type Cab = Cab or Cab = Cac, the terms cis and trans are
adequate but if three or four of the substituents are different then the nomenclature of these
geometrical isomers or diastereomers leads to ambiguity and sometimes to confusion
...
Generally E- is applied for trans-isomer and Z- is for
cis-somer when the groups of higher priority are on the same side of the reference plane, i
...
,
double bond, then the symobol (Z) is used to specify the configuration
...
For example:
2-Butenoic acid
...
blogspot
...
PM5

170

...

Q
...
Why is the RX + KOH → ROH + KX called nucleophilic substitution?
Ans
...
e
...

Q
...
How can you ascertain that X is a weakly basic group and OH is a strongly
basic group?
Ans
...

Q
...
What are nucleophilic reagents?
Ans
...
Obviously a nucleophilic reagent
attacks a molecule at the point of low electron density
...
OH, CN etc
...

Q
...
Rate equations suggest that there are two different mechanisms for
nucleophilic substitutionexplain
...
Hydrolysis of primary halogenoalkane viz
...

The rate equation is,
R = K[C4H9Br] [OH]
The suggested mechanism is:

ch

H

H

CH3

CH3

!

HO

CH3

+ : Br :
–

C

H

CH3

Br

: :

C

te

: :

H:O:

H

ht
tp
:/
/k
er
al
a

In SN2 reaction two molecules are involved in the rate determining step
...
2-bromo 2-methylpropane is first order
...
blogspot
...
PM5

171

sp

171

MECHANISM OF ORGANIC REACTIONS

...

ve

rs

O


CH3 C X + NH3 → CH3CONH2 + HX
...

bl

The mechanism shows that CBr bond breaks first to form a carbocation intermediate
...
So, SN2 is a one step
process and SN1 is a two step process
...
5
...

C

O
X

NH2

CH3

C+ X

–

NH2

gi

Here substitution of X takes place by nucleophilic NH3, so, this is an example of
nucleophilic substitution
...

te

ch

no

lo

Q
...
Of the two isomeric C4H9 Br, why does 2-bromo-2-methylpropane follow
SN1 path?
Ans
...
More the number of methyl groups, more is the dispersal of charge and more the
dispersal of charge, more is the stability of carbocation
...
2-bromo-2methylpropane ionises to give most stable 3° carbocation whereas 1-bromomethane gives 1°
carbocation
...

Q
...
What do you expect if ethanol is heated with conc
...
At first ethanol is protonated,

H

...

then a water molecule is eliminated to give a carbocation
H +
+

...

...

H H
H

C

+

C

CH2 = CH2 + H

+

H H

This reaction is an example of dehydration of an alcohol
...
blogspot
...
PM5

172

sp

172

...
This rearranges to the most stable 3° carbocation by 1,2
hydride shift
...

H

H

CH

C

CH3

2-methyl but-2-ene

ch

Q
...
Give an example of nucleophilic addition
...
First step of nucleophilic addition HCN to ethanal:

–

CH3

CH3

To complete the reaction, the negatively charged oxygen acts as a base and accepts an
H+ from HCN
...
10
...
Explain
...
blogspot
...
PM5

173

sp

ot
y
...
CH3 CH2 CH  CH 2OH + H+ → CH3CH2 CH  CH 2 O H

bl

Q
...
2-Methylbutanol on dehydration gives 2-methyl but-2-eneexplain
...
c
ot
og

ENGINEERING CHEMISTRY

sp

174

N

C

(Resonance)

rs

N

it

: :

–

:

:

–

C

y
...
The bulky group (C6 H5) surrounding carbonyl group prevents the attack of
nucleophilic (SO32) due to steric hindrance and hence the nucleophilic addition to form the
bisulphite compound does not take place
...
11
...

Ans
...
e
...

ve

So the products of the reaction are:
C2H5 Br + Ag CN → C2H5 NC + C2H5CN + Ag Br
major

minor

:

:

:

: : : :

:

–

ni

Q
...
Indentify the products of the following reaction:
Ans
...

:

:

RX + KNO2 → RONO + RNO2 + KX

gi

major
(A)

minor
(B)

(C)

lo

Q
...
Vinyl chloride does not undergo nucleophilic substitutionexplain
...

Due to resonance CCl bond attains a partial double bond character and CCl bond
energy increases and no carbocation is formed
...

Q
...
Allyl Bromide undergoes nucleophilic substitution readilyexplain
...
Allyl carbocation is resonance stabilised
+

+

CH2 = CH – CH2

CH2 – CH = CH2

and behaves as if the chlorine atom is ionic
...
15
...

+

SN1

Ans
...

+

CH2

CH2
+

CH2

+

CH2

+

Q
...
Find out the nucleophile from the following:
+

...

Ans
...

Q
...
Arrange the reactivity of the following towards nucleophilic reagent:
CH3F, CH3 I, CH3Br, CH3Cl

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH7-2
...
c
ot
og

sp

175

MECHANISM OF ORGANIC REACTIONS

OC 2H 5

ni

ve

rs

it

y
...

CH3I > CH3Cl > CH3Br > CH3F
as bond dissociation energies (D) is of the order CF > CCl > CBr > CI
...

Q
...
Aqueous KOH with RX gives alcohol whereas alcoholic KOH alkene
explain
...
In aqueous medium, SN takes place,
RX + KOH → ROH + KX
whereas in alcoholic medium
C2H5OH + KOH
C2H5OK+ + H2O
...

gi

ca

lu

RCH2CH2X → RCH = CH2
Q
...
Why do haloalkanes give cyanides with KCN and isocyanides with AgCN?
Ans
...

C ≡ N ←→ C = N

...

Ag+ promotes R+ formation from RX by precipitating AgX and reaction takes SN1 path
...
g
...
S
...
20
...
The charged species (group) that is replaced during a substitution reaction is a
leaving group
...
21
...
The stronger or harder as a base, worse as a leaving group
...
The best leaving groups are anions of
strong acids e
...
, halide ions (X)
...
22
...

Ans
...

R

R

C
R¢

Br

HO

R
Slow

OH

+

C

+

Br

R²
–

R¢

C

R¢

OH

http://keralatechnologicaluniversity
...
com
175

(±)

R

R²

C-8\N-ENGCHE\ECH7-2
...
c
ot
og

ENGINEERING CHEMISTRY

sp

176

y
...
That is, always
racemisation takes place during SN1 reaction
...
S
...

gi

Q
...
Discuss the effect of solvent on SN1 and SN2 reactions
...
The change of solvent (I) affects the rate of the reaction (II) which may change the
mechanistic pathway
...

no

The solvolysis of (CH3)3 Br becomes 3 × 104 times faster in 50 % ethanol than in ethanol
alone
...

ht
tp
:/
/k
er
al
a

te

ch

Increase in solvent polarity has little effect in SN2 reaction; only a slight decrease in
reaction rate is observed
...
The
reaction rate becomes 4
...
Because in CH3OH due to hydrogen bonding N is
3
solvated and its nucleophilic activity is reduced
...

Increase in solvent polarity and ion solvating ability may change reaction pathway from
SN2 → SN1
...

Q
...
The order of reactivity of halogen acids towards an alcohol is
HI > HBr > HCl
...

Ans
...
So, the reaction is
nucleophilic substitution and the leaving group is H2O
...

2

Nucleophilicity of X decreases in order: I > Br > Cl
...

Q
...
For a given HX, the order or reactivity of the alcohols follows the order
3° > 2° > 1°explain
...
blogspot
...
PM5

176

...
Since the stability of carbocation follow the order: 3° > 2° > 1°
...

it

y
...
26
...
Elimination reaction is a reaction that splits off a simple molecule of a compound
e
...
, H2O from a molecule of organic compound to form a double bond
...
This reaction is known as
dehydrohalogenation
...

Rate = K[RCH2CH2Br][B]

CH3CH = CHCH3 (B)

no

In substrates which have alternative β-hydrogen available, more than one alkenes can
be obtained, that is determined by two empirical rules
...

N+(CH3)3

CH3CH2 CH CH3

Y

OEt

95%

5%

Hofmann

The alkene which has
least alkyl substituents
on the double bond
carbons
...
27
...
(i) The strength of HA bond, (ii) the electronegativity of A, (iii) factors stabilising
A, (iv) the nature of the solvent
...
28
...

O


Ans
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH7-2
...
c
ot
C

H

O

+

+ H3O

C
O

y
...

it

Q
...
Justify the pKa values
pK a
4
...
05

ve

4
...
CH3 → C → O → H

lo

gi

ca

Acidity in CH3COOH is somewhat reduced due to (+I)-effect of the CH3 group and that
effect is more pronounced in (CH3)2CHCOOH and still more pronounced in (CH3)3CCOOH
...
e
...

Q
...
Justify the pKa values
Acid

pKa
4
...
66

ClCH2COOH

2
...
90

ICH2COOH

3
...
The electron withdrawing substituents with (I) effect has got marked influence
on the acidity of simple aliphatic acids
...

Q
...
Acidity order with pKa values of the following acids is:
Cl¬
Cl¬
CH COOH(pKa = 1
...
65) >
Cl
Cl
Justify
...
As the number of electron withdrawing groups increases acidity increases; pKa
value decreases
...
32
...
Explain
...
blogspot
...
PM5

178

:

¬

H

:

¬

O

sp

178

O

H

...

it
rs
ve
ni
lu

te

ch

no

lo

gi

ca

http://keralatechnologicaluniversity
...
com

ht
tp
:/
/k
er
al
a

please send ebooks questionpapers study materials
...
com so that it will be helpful to your fellow students and
teachers

http://keralatechnologicaluniversity
...
com

...

bl

(i) The electronegative atom O of phenol gets positively charged due to resonance
...
Moreover, the anion formed on the release of H+ by phenol molecule is
resonance stabilised
...

ni

ve

rs

it

(ii) Due to resonance, o- and p- positions of the benzene ring of phenol molecule become
electron rich
...
When benzene ring is attached to a group containing a key atom (here
O has lone pair of electrons) the resonance effect gives rise to increased electron
densities in the o- and p- positions
...
The electrophiles can attack at
those positions leading to electrophilic substitution
...

ca

lu

Q
...
pK a values for NH 3 , CH 3 NH 2 , (CH 3 ) 2 NH are 9
...
64 and 10
...
Justify
...

Ans
...
When this donation capacity

CH3

NH2

pKa = 10
...
77

ch

pKa = 9
...
The (+I)-effect of CH3 groups increases the
electron density of N atom in CH3NH2 and this effect is more pronounced in (CH3)2 NH due to
two CH3 groups performing as stronger bases than NH3
...
34
...
25, 10
...
62 respectively
...

+

+

NH2

NH2

NH2

:

!

:

:

+

NH2

!

:
!

NH2

:

ht
tp
:/
/k
er
al
a

Ans
...
The
pKa values are in accordance with the above fact
...
62 i
...
, it
is less basic than NH3
...

So aniline (pKa = 4
...

Q
...
Do you expect that p-nitroaniline is less basic than aniline?
Ans
...

...

*This property common to other groups, like NH2 , : OR , helps electrophilic substitution and are o-,

...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH7-2
...
c
ot
N

–

–

O

it

Å

O

O

rs

O

bl

N
pKa = 4
...

NH2

Ph NH2

og

+

:

:

ENGINEERING CHEMISTRY

pKa = 0
...
36
...

lu

ni

Ans
...
The three NO2 groups in 2, 4, 6-trinitrophenol exercise
pronounced (I) effect making the phenol molecule total acidic
...

OH

OH

NO2

lo

gi

ca

O2N

NO2
pKa = 1
...
9

Q
...
NO2 group is m-orientingexplain
...
The resonating structures of nitrobenzene are:
–

Å
Å

Due to resonance, o- and p- positions of benzene ring of nitrobenzene become electron
deficient
...
The m-position of the
benzene ring is comparatively electron-rich, that is why electrophile attacks there and msubstitution takes place
...

Q
...
Nitration of phenol is easier than that of nitrobenzeneexplain
...
In phenol OH group activates the benzene ring towards further electrophilic
substitution by enriching the electron density at o- and p- positions due to resonance
...
On the contrary,
NO2 group in nitrobenzene deactivates the benzene ring by withdrawing electrons from the
benzene ring and making o- and p- positions positively charged
...
So, nitration of nitrobenzene molecule becomes
difficult
...
39
...

Ans
...
e
...
H2SO4
...
blogspot
...
PM5

180

sp

180

...

:

: O:

T
...

Q
...
What are the electrophiles for (i) halogenation and (ii) alkylation
reactions of benzene?
Ans
...
chlorination, the reagents are anhydrous FeCl3 and Cl2
...

Cl2 + FeCl3
FeCl4 + Cl+
+ acts as an electrophile during chlorination of benzene
...
Electrophile is thus
generated
...
e
...

So, R
Q
...
Mention an organic reaction where rearrangement takes place
...
Pinacol-pinacolone rearrangement (example of 1, 2-alkyl shift)
CH3 C

te
ht
tp
:/
/k
er
al
a
!

CH3 C

CH3 CH3
C

OH

H

CH3

CH3 CH3

+

CH3 C

C

OH

OH

CH3
+

OH2

Pinacol
– H2O

CH3 CH3
CH3
C

CH3

CH3 C

CH3

:OH CH3

C

CH3

CH3 C

C
Å

OH

:OH CH3

:

+

–H

+

CH3

CH3 C
O

C

CH3

CH3

Pinacolone

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH7-2
...

og

181

MECHANISM OF ORGANIC REACTIONS

...
42
...

bl

Ans
...
Due to crowding in (I), N(Me)2 group goes out of plane of the benzene ring by free
rotation about the single bond
...
So lone pair over N(Me)2 group in (I) is available to be accepted
by a proton (H+)
...
But in (II) lone pair over
N(Me)2 comes into resonance with benzene ring and not so much available for an H+
...
43
...
Is this reaction an electrophilic substitution?
Ans
...

Classify the different organic reactions
...

What do you mean by polarisation? What is the reason behind it?

3
...

Compare the acidity among
CH3COOH, CH2Cl
...
Cl2COOH, CCl 3COOH
...

What is electromeric effect? Is it permanent?

6
...

7
...
Mention the
mechanism
...

What is polymerisation reaction? Give an example of such type of reaction with plausible mechanism
...

What do you mean by electrophiles and nucleophiles?

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH7-2
...
c
ot
og

10
...

bl

11
...

12
...

it

13
...

rs

14
...
Explain with proper mechanism involved with
examples
...
What is resonance? State the important features of it
...
What are the significances of the terms:

ni

(i) Resonance hybrid and (ii) Resonance energy
...
What is elimination reaction? Describe different types of elimination reactions
...
Heat of hydrogenation value of 1, 3, 5-cyclohexatriene is 85
...
8 kcal/moleexplain
...
Write a short note on hyperconjugation
...
What do you mean by 1, 2-shift
...
Compare the basicity among the following:

NMe2

lo

NH2

NMe2
Me

Me

,

no

,

ht
tp
:/
/k
er
al
a

te

ch

22
...

23
...

24
...
Name them as per RS
nomenclature
...
Draw the resonance structures of:
(i) phenate ion
(ii) acetate ion
(iii) chlorobenzene
(iv) butadiene
...
Draw all the Fischer projection formulae of:
(i) glyceraldehyde
(ii) lactic acid
(iii) tartaric acid
(iv) 2, 3-dibromopentane
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH7-2
...
c
sp

ot
y
...

In a solution a weak electrolyte dissociates reversibly
...

If for a weak acid the degree of dissociation is α, then
H+ + A
Cα Cα

ht
tp
:/
/k
er
al
a

∴

te

ch

When C = concentration of HA
Ka =
α=

[H + ] [A − ] C α
...
mol
...

2
Ka = V V = V
1− α
1− α
V
V

Ka =
α=

[as α is negligible]

...
(2)

The expression which relates the variation of degree of dissociation (α) of a weak
electrolyte with dilution is known as Ostwalds dilution law
...

Putting C = 1 we get α =

Ka

i
...
, the degree of dissociation of a normal solution of a weak electrolyte is approximately equal
to the square root of its ionisation constant
...
blogspot
...
c
ot
og

sp

185

IONIC EQUILIBRIUM

bl

Common Ion Effect

H+ + OAc , NaOAc → Na+ + OAc

AcOH

it

[H + ] [OAc − ]
[AcOH]

...

If we add NaOAc to a solution of AcOH, the ion ( OAc ) becomes common
...

lu

ni

ve

Now, NaOAc being a salt dissociates completely in solution
...
e
...
As a result, the dissociation of AcOH will be suppressed
...
In general, we can say, that common ion
effect suppresses the dissociation of a weak electrolyte in solution
...
It is well known
that in neutralisation reactions, acids react with alkalies to form salts and water
...
e
...

ht
tp
:/
/k
er
al
a

Bronsted and Lowry Concept
Arrhenius theory is suitable in explaining the reactions of acids and bases in aqueous
solutions but it fails to explain the following reactions, specially in non-aqueous solvents
...

2NaNH2 + MgSO4 = Mg(NH2)2↓ + Na2SO4 (in liq
...
e
...
The definition of acids and base needs to be extended
...
These species may be neutral or charged
...
The strengths
of the acids or bases may be determined by their tendencies to donate or accept a proton in a
definite solvent
...

As for example, Cl is a conjugate base of the acid HCl and HCl is the conjugate acid of
the base Cl
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH8-1
...
c
ot
ClO
OH
SO4=
CO3=
NH3
[Cr(H2O)5OH]+2

y
...
Solvent behaves as
a base towards acid and vice versa
...

ht
tp
:/
/k
er
al
a

te

ch

Highlights:
• HClO4, HBr, H2SO4, HCl and HNO3 are of same strengths in water; but in glacial
acetic acid their strengths are as follows:
HClO4 > HBr > H2SO4 > HCl > HNO3
This phenomenon in water is known as levelling effect of water
...

CH3COONa → CH3COO + Na+; H2O
H+ + OH
is a strong base as its conjugate acid, acetic acid
According to Bronsted, CH3COO
is weak
...
As a result, the solution will get enriched with OH ions and
will behave alkaline
...

Classification of Solvents
Solvent

Example

(i) Protophilic (Proton seeking)
(ii) Protogenic (Proton generating)
(iii) Amphiprotic (Both proton seeking
and generating)
(iv) Aprotic (Independent of proton
seeking and generating)

H2O, NH3
H2O, CH3COOH, HF
H2O, EtOH
C6H6, CCl4
...
blogspot
...
PM5

186

sp

186

...

bl

An acid is a substance which can accept a pair of electrons and a base is a substance
which can donate a pair of electrons
...

N ¾® AlCl3

Acid
Base

ca

N + AlCl3

Salt

CO
Base

CO

Cl
O ¾® B

Cl
Cl

lo

:

gi

Cl
O: + B

:

CO

CO
Salt

no

Acid

Cl
Cl

ch

• A substance can behave as an acid even though it does not donate a proton, this
phenomenon can only be explained by the Lewis concept
...
It ionises as follows:
H2O
H+ + OH
or more correctly, 2H2O
H3O+ + OH
...
Therefore,
K[H2O] = [H+][OH]

or
Kw = [H+][OH]
Kw is known as ionic product of water, its value at 25°C is 1 × 1014
...

• Dissociation constant of water and ionic product of water are not same
...
It is
worthwhile to mention that an aqueous solution always contains H+ and OH ions
...
Again an alkaline solution contains

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH8-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

188

bl

H+ ions though in small concentration
...

0

1

2

3

4

pH scale
5

6

7

8

9

10

11

12

13

14

no

pH

lo

gi

ca

lu

ni

ve

rs

it

y
...
ion l1
...
ion l1
...
01 (N)
strong alkali solution contains [OH], 102 g
...
Therefore, hydrogen ion concentration of the solution will be 1012 g
...
In pure
water [H+] = [OH] = 107
...
And in the solution where the [H+] becomes less than that of [OH], the solution
becomes alkaline
...
ion l 1
...
66 × 10
solution in such a manner
...
P
...
Sorensen (1909) simply applied negative logarithm of hydrogen
ion concentration to remove this sort of difficulty for expressing such concentrations
...
He
defined pH as negative logarithm of hydrogen ion concentration:
pH = log10 [H+]
A more convenient scale for expressing concentration of H+ ion in aqueous solutions is
thus developed
...

Therefore, in any aqueous solution pH + pOH = 7 + 7 = 14
Highlight:
or,
∴

log10

[H+]

[H+] × [OH] = Kw
...

Pure water is neutral because in pure water, [H+] = [OH] = 107
...

Highlight:
Following such conventions we express Ka and Kb as follows:
pKa = log10 Ka, and pKb = log10 Kb
As for example: Ka for salicylic acid = 103
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH8-1
...
c
ot
og
bl
y
...
Calculate pH of the following solutions:
(a) 4
...
0016 (N) base
...
Both acid and base are strong
...
So,
(a)
[H+] = 4
...
9 × 104)
∴
pH = 4 log10 4
...
69 = 3
...
6 × 103 g-ion l1
log10 [OH] = log10 (1
...
6 = 3 0
...
7959 or 2
...
76 = 11
...

Example 2
...
63
...

pH = 3
...
63

gi

log10 [H+] = 3
...
63 = 4 0
...
37

ht
tp
:/
/k
er
al
a

te

ch

no

lo

[H+] = antilog 4
...
34 × 104
∴
[H+] = 2
...

Example 3
...
1(N)]
...
013
...

[OH] = 0
...
1 = 1
...

10 −14
= 7
...

1
...
7 × 1012) = 12 log 7
...
8865 = 11
...

[H+] =

Relative Strengths of Acids and Bases

Tendency of donating protons in any aqueous solution is a measure of acidity of the
solution
...
There are several other processes for comparing strengths of acids
...

Let, degree of dissociation of acid A1 = α1
Degree of dissociation of acid A2 = α2
The concentrations of the acids were same (C)
...

Buffer Solutions
Some solutions do not change their pH on addition of little acid or alkali
...
The arrest of pH changes of these solutions is known as buffer
action
...
blogspot
...
PM5

189

sp

189

IONIC EQUILIBRIUM

...

bl

Mechanism of buffer action: A buffer solution is generally a mixture of solutions of a
weak acid HA and its salt BA
...
So A will readily accept H + from
A
solution which comes from the added acid to the solution
...
So the change of pH will be
arrested
...

So, pH of such solution will not change on addition of little acid or alkali and that is the
buffer action of the solution
...

As in this case,
BA → B+ + A
(complete dissociation)
+ + OH
BOH
B
(incomplete dissociation)
On addition of acid to such solution, external H+ will be removed by BOH
H+ (external) + BOH → B+ + H2O
...

B
So the pH of the solution will not change on the addition of a little acid or alkali
...

∴

pH = pKa + log10

This is the famous Henderson equation
...
blogspot
...
PM5

190

...

bl

The acidity or alkalinity of mixed solution, i
...
, pH depends upon the ratios of the
concentration of salt and acid
...
e
...

(ii) Buffer solution (prepared from a weak base and its salt)
In this case:

rs

Kw
[B + ] [OH − ]
[B + ]
=
×
[BOH]
[BOH] [H + ]
K
[B + ]
[H+] = w
...

[B + ]
[Salt]
= pKw pKb log
[BOH]
[Base]

lu

pH = pKw pKb log

ca

∴

lo

gi

Highlights:
• Buffer solution almost invariably consists of a mixture of a weak acid HA and its
salt BA or a mixture of weak base BOH and its salt BA
...

te

Different Buffer Solutions

ht
tp
:/
/k
er
al
a

Component conjugate acidbase pair
(i) Glycine/Glycine hydrochloride

(ii) Phthalic acid/Potassium hydrogen phthalate

(iii) Acetic acid/Sodium acetate
(iv) NaH2PO4/ Na2HPO4

pH ranges
1
...
7
2
...
38
3
...
6
5
...
8-9
...
Prepare a buffer solution of pH 5
...
76]
...
76 + log
[Acid]

Sol
...
76 = 5
...
76 = 0
...

[Acid]
[Salt]
= antilog (0
...
738
[Acid]

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH8-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

192

bl

Therefore, when 1
...

y
...
But it can be successfully applied to the
saturated solutions of sparingly soluble salts, because a heterogeneous equilibrium is set up as
follows
...
By convention it is unity
...

Therefore,
[B+] [A] = constant = Ksp
...
The above equation
signifies that the product of concentrations of B+ and A of a salt is constant independent of the
individual concentrations of B+ and A ions when temperature is constant
...
mol l1 and [A] = S g
...
l1
...
Sx+y
It is a universally applicable equation
...
l1
Mg3(PO4)2(s)
Mg3(PO4)2 (Solution)
[Mg+2]3

[PO43]2

(3C)3

(2C)2

C5
...

• It is customary to express the concentrations of the ions in g
...
e
...
equiv
...

The solubility product of a salt may be defined as the greatest possible product of
concentrations of its constituent ions in its saturated solution expressed in g
...
ions of each type
formed by dissociation of one molecular formula weight of the salt
...
The solubility of chalk is 0
...
Calculate its solubility product
...

wt
...
0305 gl1 = 3
...
05 × 104)2 = 9
...

Example 2
...
0002 mol l1
...

CaF2
Ca+2 + 2F

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH8-1
...
c
ot
Effect of Common Ion on Solubility

og
bl

[Ca+2] = 0
...
[F] = 2 × 0
...

Ksp = [Ca+2] [F]2 = 0
...
0004)2 = 3
...

ve

rs

it

y
...
As a result, the concentration of other ion will decrease
otherwise the constant Ksp will change
...

ni

Highlights:

ca

lu

• It is almost invariably true that addition of a common ion at first diminishes the
solubility of a sparingly soluble salt but when relatively large amounts are added
the solubility starts to increase
...

lo

gi

Example
...
(a) At 25° the solubility of BaSO4 is 0
...
Calculate the solubility
product of the salt, taking complete dissociation
...
2 gl at
25°C
...
00233
= 105 g
...
[SO4=] = 105 × 105 = 1010
...
(a)
∴

13
...
1 (M)
132
∴
[SO4=] = 0
...
ion l1
...

∴
Ksp = S′ × (S′ + 0
...

te

[(NH4)2SO4] =

ht
tp
:/
/k
er
al
a

(b)

∴

S′ =

10 −10

[S′ is negligible compared to 0
...
l1
...
33 gl1
...
A litre of a solution contains 0
...
001 g
...
To
arrest the precipitation of Mg(OH)2
...
8 × 105 and K sp Mg(OH) = 1
...

4

2

Sol
...
12 × 1011
∴

[OH]

L 1
...
001 Q

−11 1/2

= 1
...
ion l1
...
1 × 104 g
...

For doing so, we are to suppress the dissociation of NH4OH by adding common ion NH4+
...
8 × 105
...
blogspot
...
PM5

193

sp

193

IONIC EQUILIBRIUM

...
1 × 10 −4
4
= 1
...
01

∴ [NH4+] = 1
...
ion l1
...

Effect of a Salt without a Common Ion on Solubility

it

For the correct expression for solubility product we should use activity (a) in place of
concentration: i
...
, Ksp = aAg +
...

rs

So, true expression is Ksp = γ Ag +
...
γ Cl− [Cl − ]

lu

ni

ve

Q
activity (a) = Concentration (c) × activity coefficient (γ)
∴
a = cγ
...

If we add KNO3 to a saturated solution of AgCl the γ-term of the expression of Ksp
decreases
...
[Cl] increases in order to keep the true Ksp value constant
...
This effect is known as salt effect
...

• The effect of common ion on solubility is utilised in qualitative inorganic analysis
to separate the ions present in a solution
...
A
salt may not get precipitated even when its ionic product exceeds its solubility product
...
That is why, for precipitation in chemical analysis,
the value of solubility product of the salt should always be higher than its ionic product
...
The chlorides of Group I metals (Hg2+2, Pb+2, Ag+) are insoluble, on addition of
dil
...
Only PbCl2 has higher solubility product and for that reason it is not completely
precipitated here
...

Group II
...
HCl
...
So concentration of sulphide ion CS= remains low
...
e
...
IIIB metallic ion (Co+2, Mn+2,
Ni+2, Zn+2) sulphides have higher values of solubility products, so their precipitation is arrested
here, CdS and PbS have comparatively higher values of solubility products, so CS= should be
high for them
...
Again diluted acid medium
precipitates colloidal As2S3 and SnS which creates difficulty in filtration
...

Group III A
...
The common NH 4+ suppresses the
dissociation of weak base NH4OH thereby COH remains low
...
The precipitation of

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH8-1
...
c
ot
og

sp

195

IONIC EQUILIBRIUM

y
...

Group IV
...
Group IV metals i
...
,
+2, Ca+2, Sr+2 are precipitated as carbonates
...

pH = 14 2 = 12
...
Calculate the pH of 0
...

Sol
...
005 = 102 mol
...

lu

Example 2
...
1 M HCl to 1 litre
...
1
= 0
...

1000
∴
pH = log10 [H+] = log10 [2 × 10 3]
= 3 log 2 = 3 0
...
6990 ~ 2
...
7 = 11
...
3
[OH] = 1011
...
01 × 1012 g
...

Example 3
...
0 × 10 8 (M) HCl solution
...

Sol
...
But when it exceeds 106, the contribution of H+ ions is to be counted during
calculation of pH
...

So, the [H+] of the solution = (1 × 108 + x) and [OH] = x
∴
Kw = [H+] [OH]
= (1 × 108 + x) × x = 1014
...

∴

∴

− 10 −8 ± (10 −8 ) 2 + 4
...
10 −14
2×1
8 (M)
= 9
...
0 × 108 + x) = (1
...
5 × 108)
[H
x=

= 10
...
5 × 108)

= 8 log10 10
...
98
...

total [OH] = (1 × 108 + x)
[H+][OH] = Kw = 1014

∴
So,

(1 × 108 + x) × x = 1014

∴

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH8-1
...
c
ot
∴

og

ENGINEERING CHEMISTRY

x2 × 1
...
5 = 6
...
98 = 7
...

y
...
5 × 108 (M)
[OH] = 9
...
ion l1

it

∴
∴

=

[H + ] [CH 3 COO − ]
[CH 3 COOH]

ve

lu

Ka =

0
...
2C 0
...
02)
0
...
(a) Calculate the molar concentration of an CH3COOH solution
...
8 × 105
...
02)
(b) Calculate the degree of dissociation of 0
...

Sol
...
8 × 10 −5 × 0
...
004
= 0
...

c=

lo

∴

Ka

no

1
...
24 × 102
...
01
Example 5
...
1 mole CH3COOH and 0
...
Calculate the pH of buffer solution
...
74)
...
According to Henderson equation pH of a buffer solution
α=

=

ht
tp
:/
/k
er
al
a

te

ch

(b)

pH = pKa + log

[salt ]
[acid]

0
...
74
...
1

Example 6
...
4
...
Given Ka of
H2CO3 = 4
...

Sol
...
74 + log

∴
∴

Ka =
−
[HCO3 ]

[H 2CO 3 ]

=

−
[H + ] [HCO 3 ]
[H 2 CO 3 ]

Ka

[H + ]

=

4
...
5 × 10 −7
=
_
~
[H + ]
3
...
4
∴
log10 [H+] = 7
...
4 = 3
...
ion l1
Example 7
...
45 × 1011
...

Sol
...

= 4S3

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH8-1
...
c
ot
og
bl

4S3 = 3
...
45 × 10 −11
mole l1
4
= 2
...

Example 8
...
1M NaF solution
...

Sr+2 + 2F
Sol
...

S=

2S mole

ve

S mole

Initially = in 0
...
1) mol
...
1)2 = 0
...

0
...
1
...

Ans
...

For weak electrolytes, α is negligibly small,

ht
tp
:/
/k
er
al
a

So,

1α≈1

K

...
2
...
An acid is a substance which in aqueous solution gives H+ ions
...

Thus, HCl is an acid and NaOH is a base
...
3
...
An acid is a species (neutral or charged) which can donate a proton and a base is a
substance or species (neutral or charged) which can accept a proton
...

and HSO4

Q
...
What are conjugate acid-base pairs?
Ans
...
This sort of pairs are known as conjugate acid-base pairs
...
HSO4 is a conjugate base of H2SO4
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH8-1
...
c
ot
og

ENGINEERING CHEMISTRY

y
...

NH4+/NH3 and so on
...

Q
...
Show that solvent acts as a base or an acid according to Lowry Bronsted
concept
...
According to Lowry Bronsted concept acidbase reaction always follows the equation:
+
BaseII
AcidII
+
BaseI
AcidI
CH3COOH +

H3O+

+

F
OH

lu

H2O

no

H

base

te
ht
tp
:/
/k
er
al
a

H

...

acid
H
base

ch

acid

...

lo

gi

ca

So, every acidbase reaction proceeds according to the equation i
...
, conjugate acids and
bases are formed during the reaction,
AcidI
+
BaseII
AcidII
+
BaseI
Q
...
Give Lewis concept of acids and bases
...
An acid is a species which can accept a pair of electrons and a base is a species
which can donate a pair of electrons
...
7
...
8 × 1016
...

H2O + H2O
or

H+ + OH

H2O

K=

[H3 O + ] [OH − ]
[H 2 O]

or

[H + ] [OH − ]
[H 2 O]

1000
= 55
...

18
Kw = K [H2O] = [H+] [OH] = 1
...
5555

[H2O] =

= 100 × 1016 = 1
...

Q
...
In pure water, what will be the [H+] or [OH]?
Ans
...
ion l1
...
blogspot
...
PM5

198

sp

198

...
9
...

Q
...
Explain the pH scale
...

bl

Ans
...
e
...
The pH scale is a logarithmic scale for measuring the concentration of hydrogen
ions in aqueous solutions
...
ion l1
In acidic solutions, [H+] range

ve

In neutral solutions, [H+] = [OH] = 107 g
...

ni

In alkaline solutions, [H+] range = 108 1014 g
...

lu

pH = log10 [H+]
0

1

2

3

4

5

6

7

8

9

[H+] =

10 0

10 1

10 2

10 3

10 4

10 5

10 6

10 7

108

10 9

←

neutral

→

10

11

12

13

14

1010 10 11 10 12 1013 10 14

alkaline

gi

acidic

ca

pH =

ht
tp
:/
/k
er
al
a

te

ch

no

lo

Q
...
What is the pH of 0
...

pH = log10 [H+]
= log10 [2 × 102] (as the acid is strong)
= log10 2 + 2 log10 10
= 2 0
...
699 ≈ 1
...

Q
...
What is the hydrogen concentration of coca cola with pH 2
...

pH = 2
...
3
or
log10 [H+] = 2
...
3
= 5 × 103 mol dm3
...
13
...

Ans
...

Phenolphthalein

pH 7

pH 7
Methyl
orange

0

0
0

25
Alkali(c
...
)
Strong acid–strong base

0

25
Alkali(c
...
)
Weak acid–strong base

Fig
...
1 Neutralisation Curves
...
blogspot
...
PM5

199

sp

199

IONIC EQUILIBRIUM

...

it

y
...
8
...
It is to be noted that, at the equivalence
point, when exactly equal amounts of acid and alkali have been added, the pH is not always
neutral
...
14
...

ni

ve

Ans
...
When a salt formed at the equivalence point has either a parent acid or a parent
base weak, it hydrolyses to give a solution that is not neutral
...

ca

lu

Weak acid/strong base end point is alkaline (pH > 7)
Strong acid/weak base end point is acidic (pH < 7)
...

gi

Q
...
Neutralisation is essentially a reaction between H+ and OH ions in
aqueous solutionexplain
...
16
...

This experimental evidence supports the above view
...
pK is the logarithmic form of an equilibrium constant, useful for pH calculations
...

ht
tp
:/
/k
er
al
a

Q
...
How can you use pK values for pH calculations?
Ans
...

(ii) pH of a weak acid = pH =

c = concentration of undissociated acid
...

(iii) pH of a weak base = 14

Kb = dissociation constant of weak base
...
18
...
02 mol
...
NaOH is a strong base
[OH] = 0
...
02 = 1
...
7 = 12
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH8-1
...
c
ot
−
[H 3 PO4 ]

2

3

2

Q
...
Relate Ka, Kb and Kw
...
(i) HA + H2O

–

(ii) A + H2O

te

og

lo

Ka × Kb =

ht
tp
:/
/k
er
al
a
or

–

[HA] [OH − ]

no
ch

Kb =

∴

ca

[H 3 O + ] [A − ]
[HA]

HA + OH

Conjugate pair

Now,

base

Conjugate pair

Ka =

–

gi

acid

H3O + A

lu

1

ni

Ka > K > Ka
...

−
[H + ] [H 2 PO42 ]

H+ + HPO42; K a =

(ii) H2PO4

it

1

−
[H + ] [H 2 PO 4 ]
[H 3 PO 4 ]

rs

H+ + H2PO4; K a =

(i) H3PO4

bl

Q
...
H3PO4 has three Ka valuesexplain
...
There are three dissociations for H3PO4 and accordingly ka values
...

Ka × Kb = Kw

log Ka log Kb = log Kw

∴

pKa + pKb = pKw = 14
...
21
...

Ans
...

(ii) A small variation of pH of human blood (6
...

(iii) pH value helps to determine the condition of reactions in laboratory and in industry
...
22
...
The change in equilibrium position due to addition of an ionic compound that
contains one of the ions involved in the equilibrium is known as common ion effect
...

(ii) The common ion effect influences the behaviour of buffer solution
...

Q
...
What is a buffer solution?
Ans
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH8-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

202

100

...
40
= 3
...
4 = 4
...

1
...
1 × 1022
[H 2S]

(0
...
01) [S −2 ]
=
[H 2 S]
0
...

∴

+

2H+ + S2; K =

H2S

∴

FG N IJ H
H 100 K

rs

containing

ni

Ans
...
1M]

lu

Q
...
Will

y
...
1 × 1019 = 1020

gi

Ksp
...
4 × 1015
So, ppt
...

ca

Ans
...
24
...
4 mol dm3 methanoic
acid and 1
...
8
...

6
...

Deduce Ostwalds dilution law and state its limitations
...

Explain the terms: (i) Buffer solution (ii) Buffer capacity and (iii) Buffer action
...

Which are the strongest Lewis acids in the series? (a) BF3, BCl3, BI3; (b) BeCl2, BCl3
...

The reaction HCl (aq) + KOH (aq) → KCl (aq) + H2O is neutralisation according to:
(a) Bronsted-Lowry concept, (b) Lewis theory and (c) Solvent system concept
...

Deduce the Hendersen equation and state its utility
...
Show that it is different from dissociation constant of water
...

What is the basic equation for acid-base reaction of Bronsted theory?
Explain (a) neutralisation, (b) hydrolysis, in the light of Bronsted theory
...

Derive an expression for pH of the buffer solutions:
(a) Weak acid and its salt
...

What is pH? Give its importance and usefulness
...

Discuss the effect of common ion on solubility product
...

2
...

4
...

9
...

11
...

13
...

15
...

17
...

19
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH8-1
...
c
ot
og

sp

203

IONIC EQUILIBRIUM

bl

21
...
05 (N) NaOH and 200 ml of 1N
HCl?
[Ans
...
3]
[Ans
...
Find α for NH4OH in a solution of
...
Given Kb = 2 × 105
...
014]

y
...
Calculate the pH and pOH of
...

it

24
...
of CH3COOH and 7
...
of CH3COONa,
making a volume equal to 500 ml?
[Ans
...
78]
25
...
57
...

[Ans
...
69 × 1011 moles l1]

(b) 0
...
00345 (N) acid

rs

26
...
00886 (N) base

[Ans
...
46, 11
...
11, 10
...
95, 2
...

27
...
038 g-l1
...

Calculate its solubility product
...

[Ans
...
6 × 108]
[Ans
...
4 × 1012}

in a solution is 4 ×
g-in
Calculate the minimum concentration of Cl to precipitate
10
...
5 × 108 g-in l1]
AgCl
...
8 × 10

ca

29
...
Solubility of Ag2CrO9

g-l1
...
Calculate the concentration of H2S required to arrest the precipitation of PbS from a solution of
[Ans
...
6 (M)]
0
...
Given Ka(H2S) = 1
...
4 × 1028
...
blogspot
...
PM5

203

...

it

9

ve

rs

Electrochemistry

ni

INTRODUCTION

lo

gi

ca

lu

Substances behave differently towards electric current
...
Substances which conduct electricity are conductors, as for example, metals, acids, bases
etc
...
Again conductors can be divided into two subdivisions: (i) electrolytes and (ii) nonelectrolytes
...
e
...

Substances which conduct electricity and get dissociated in solution or in the fused states were
termed electrolytes by Faraday
...

Table 9
...

• It involves no chemical change during
conduction of current
...

• Chemical change takes place i
...
, new products are obtained during conduction of
current
...

Electrolysis

Dissociation of a compound by passing electric current through a compound in solution
or in fused state is known as electrolysis
...
9
...

The current is always passed into and out of the electrolyte by means of metal foils or plates
Battery
+
–

Anode

Cathode

+

–

Voltameter

Electrolyte

Fig
...
1 Set-up for electrolysis
...
blogspot
...
c
ot
og

sp

205

ELECTROCHEMISTRY

it

y
...
They are electrodes (cathode and anode)
...
When an electrolyte
(electrically neutral) is dissolved in water (or in fused state), it breaks up into two or more ions
of two different kinds, positive and negative, the amount of positive charge being exactly equal
to the amount of negative charge
...

Na+ + Cl, NaOH

NaCl

Na+ + OH etc
...
This
dissociation is complete at infinite dilution
...
The anions migrate towards the anode and cations migrate towards
the cathode
...
This theory of electrolytic dissociation was first put forward by Arrhenius, that is
why the theory is known as Arrhenius ionic theory
...

gi

If W = the mass of ion liberated in gms,
t = the time in secs,

lo

c = the current strength in amperes,

then according to first law:

no

Q = the quantity of electricity in coulombs,

ch

W ∝ Q but

∴

Q=c×t

W ∝ ct

te

∴ W = Zct where Z is a constant
...
e
...
e,
...
Z is called electrochemical
equivalent (E
...
E
...

+

+

–

+

1

–

–

+

2

H2O + Acid

CuSO4 solution

3

AgNO3 solution

Fig
...
2 Different voltameters containing different electrolytes
...
blogspot
...
PM5

205

–

...
5/2 g Cu will be liberated in
cell (2) and 108 g Ag will be liberated in cell (3) (Fig
...
2)
...

Let, the quantity of electricity = Q coulomb
the quantity of Cu deposited = W1 g

it

the quantity of Ag deposited = W2 g
Then, according to Faradays second law:

ve

(from the first law)

E1 E2
=
Z1 Z2

or

or E ∝ Z

ni

E1 Z 1
=
E2 Z 2

∴

rs

W1 E 1 Z 1Q
=
=
W2 E2 Z 2 Q

lu

So chemical equivalent of an element is proportional to its electrochemical equivalent
...
C
...
of hydrogen = ZH, E
...
E
...
008
1
So, E
...
E
...
C
...
of hydrogen
...
of any element during electrolysis, the quantity of
electricity is fixed
...

When

∴

F=Q=

∴

or

W = E, Q =

W = KQE =

1
K

(for 1 gm
...
)

QE
F

From first law, W = ZQ
E = ZQ (for 1 gm
...
)
= ZF

or

F=

E
Z

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH9-1
...
c
ot
og

E
E 1 E2
=
=
...

1
...
0000104

107
...
0001118

Cu

31
...
0003294

O

8
...
0000829

lu

ni

Ag

ve

H

Z

rs

E

it

Table 9
...

bl

for one gm equivalent of different elements

Element

96496
96495
96494
96495
≈ 96500

no

lo

gi

ca

The concept of transport number
...
e
...
If 100 cations cross the barrier from left to right, then
current is wholly carried by cation
...
The case may be totally reversed,
in that case, the transport number of anions is hundred per cent and that of cations is zero
per cent
...
9
...

te

ht
tp
:/
/k
er
al
a

D
E

a
C
A
T
H
O
D
E

ch

A
N
O

b

Fig
...
3 Concept of transport number
...
For example, if 80 cations cross
the barrier (ab) towards cathode compartment and 20 anions cross the barrier (ab) towards
anode compartment, the total quantity of the current passed will remain same as above i
...
,
100 units but the current carried by cations is 80 per cent and the current carried by anions is
20 per cent
...
So,

transport number (t) =

ni Z i
Σ ni Z i

where, ni = number of the ions and Zi = valency of the ions which cross the barrier
...

So, t+ ∝ u and t ∝ v and (t+ + t) ∝ (u + v)
But
t+ + t = 1
v
u
∴
t+ =
and t =
u+ v
u+ v
where u and v are the speeds of cations and anions respectively
...
blogspot
...
PM5

207

sp

207

ELECTROCHEMISTRY

...

+

it

y
...
The current I is flowing, the solution contains n(±) number of ions per millilitre

B

+

lu

–

ni

ve

A

rs

–

+

–
v

+

gi

ca

u

lo

Fig
...
4 Voltameter
...
The number of ions liberated at the positive and negative
electrodes per unit area are given by n+ u and n v
...
9
...

ht
tp
:/
/k
er
al
a

The total current carried by the positive and negative ions = I = I+ + I
= (n+u)z+e + (nv)ze
...

The following model will make the idea clear (Fig
...
5)
...
blogspot
...
PM5

208

...

Anode
compartment

+

o

ca

a

gi

Fig
...
5 Scheme showing the equivalence of discharge for any
relative rate of motion of the two ions
...
Let there be total 14
molecules in the electrolyte
...

ht
tp
:/
/k
er
al
a

te

ch

(ii) When only the anions move
...
The cations did not move at all
...

(iii) When the anions and cations move at the same rate
...
In this case also, the number of anions and cations discharged is the same i
...
,
four, but the concentration of both the compartments has fallen to the same extent
i
...
, by two molecules due to deposition of ions at the respective electrodes
...
Let when two cations have crossed
the diaphragm towards the cathode, one anion passes towards anode
...
The total number of cations and anions discharged is again the same
three
...

It is evident from the above discussion that the fall of concentration around an electrode
is proportional to the speed of the ions moving away from it
...
blogspot
...
PM5

209

sp

209

ELECTROCHEMISTRY

...
equivalence liberated from both the compartments is proportional to (u + v)
...

Total number of equivalence of the electrolyte liberated on the electrode

it

y
...
The three tubes are fitted with
stopcocks
...
A dilute
AgNO3 solution (N/20) is taken for electrolysis
...
01
to
...
is passed for a period of 23 hours through the
AgNO 3 solution
...
After a definite time, the current is
stopped
...
9
...

rs

Determination of Transport Number (Hittorfs Method)

+

A

gi

ca

B

lo

e

Let,

no

The solution collected from anode (anolyte) = x g

ch

The amount of AgNO3 in x g anolyte

=yg

te

The amount of water containing
y g
...
9
...
Transference number
determination by Hittorfs method
...

Weight of silver deposited on cathode in the coulometer = w g
...

108

If no migration would have taken place, the total weight of AgNO3 should have been
present (x y) g of water in the anode compartment = (W + z) g
...

tAg + =
tAg + =

∴

No
...
of AgNO3 lost from anode compartment due to migration
No
...
of silver deposited in the coulometer
W ( y Z) × 108
170 × w

tNO

3

= 1 tAg +

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH9-1
...
c
ot
og

sp

211

ELECTROCHEMISTRY

0
...
02

0
...
10

0
...
444

0
...
396

0
...
127

it

Concentration (N)

y
...

0
...
003

rs

It is obvious that Cd+2 is moving towards anode in larger amounts than the
cathode and that is the cause of decrease of tCd+ 2
...

Let, CdI2 ionises as follows in a concentrated solution:
Cd+2 + [CdI4]2
2CdI2
+2 ion is moving towards both cathode and anode and towards anode due to
i
...
, Cd
above complex ion formation
...
This is true for other complex compounds too
...
In an electrolysis of CuSO4 between copper electrodes the total mass of
copper deposited at cathode was 0
...
79 and 0
...
Calculate the transport number

of the Cu++ and SO4 ions
...
of Cu+2 in the liquid per unit vol
...
79 g
...
of Cu+2 in the liquid per unit vol
...
91 g
...
due to dissolution of Cu anode during electrolysis = (0
...
79) g = 0
...

ch

Increase in wt
...
153 g
...
would have been 0
...

ht
tp
:/
/k
er
al
a

te

But actual increase = 0
...

Fall in concentration due to migration of Cu+2 ions = (0
...
12) g = 0
...

∴ Transport number of Cu++ ( tCu + + ) =

0
...
215
0
...
215) = 0
...

Example 2
...
916 during electrolysis of a silver nitrate solution
...
916
−
v
Speed of NO 3
r=

1
u
1 n
=
(n = tNO 3 ) or n =
1+ r
v
n

n = tNO 3 =

1
= 0
...
916

tAg + = 1 tNO = 1 n = (1 0
...
479
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH9-1
...
c
ot
R=ρ
...

where ρ = constant, its value is dependent on material of the conductor and is known as specific
resistance
...

ve

The reciprocal of specific resistance is termed specific conductance or specific
conductivity (K, Kappa)
...
=
= ohm1 cm1 = mho cm1
ρ a R cm 2 × ohm

K=

ca

lu

If a solution acts as an electrolyte, the specific conductivity of the solution is known as
Kv, i
...
, it is the conductivity of 1 cm3 of the solution
...
e
...

ch

no

If C is the concentration of the solution in g-equivalent l1, the volume of the solution
containing 1 g-equivalent will be 1000/C
...

=

l 1

...

a R

OP
Q

cm × 1 × cm 3
cm 2 × ohm × g
...
equivalent1
...
If M is the concentration in moles l1, then

1000 K
M
1 cm2 mole1
...

But the value of λv or λm actually increases with dilution as it is the product Kv × V and on

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH9-1
...
c
ot
og

sp

213

ELECTROCHEMISTRY

it

y
...
After a certain dilution there remains no
more electrolyte molecule to ionise and then there is no change i
...
, no increase of λv or λm with
dilution
...

Table 9
...
0982

0
...
00132

0
...
05115

0
...
001005

0
...
01119

0
...
00024

0
...
001225

0
...
001

0
...
0001

0
...
2

41
...
3

49
...
01

111
...
1

2
...
000143

122
...
2

14
...
0000752

0
...
6

75
...
0

0
...
0000107

129
...
8

107
...
82

gi

ca

lu

1
...

Such electrolytes are called strong electrolytes
...
Such electrolytes whose λv values
increase with dilution are known as weak electrolytes (see Fig
...
7)
...
9
...

Experimental Determination of Specific Conductance (K)
The arrangement of apparatus adopted for the determination is modified Wheatstones
meterbridge arrangement (see Fig
...
8)
...
The products of electrolysis will accumulate on the
electrodes which will change the effective resistance
...
C
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH9-1
...
c
ot
y
...
C
...
9
...

ca

Fig
...
8 Determination of conductivity of solutions;
C is a compensating condenser (adjustable)
...
C
...
9
...

The solution whose conductance is to be measured is put into the conductivity cell (see
Fig
...
9)
...
Conductivity water (double distilled water) should be used throughout
...
9
...
Connections are made by Pt
wires
...
But the procedure is to calculate a
factor for each cell known as cell constant (x)
...

l
=ρ×x
s

The cell constant is known by determining the conductance of

FG N IJ KCl solution
...
002768 ohm1
...

Specific conductance K = x × Observed conductance
...
blogspot
...
PM5

214

...
002768
...

cell constant being known it is easy to obtain the specific conductance of any solution by using
the above relation
...

• According to equation:
K = x × observed conductance
...

ca

lu

ni

ve

rs

• It should be noted that cell constant (x) =

Kohlrauschs law (Law of independent migration of ions)

lo

gi

At 25° the equivalent conductance at infinite dilution (λ∞) values for some electrolytes
are given in the table below:
Table 9
...
volt

Anion

λa

Mobility, V
cm2/sec volt

197
...
00205

349
...
00362

OH

73
...
00076

1
SO4
2

79
...
00083

NH 4+

73
...
00076

Cl

76
...
00079

Ag+

61
...
00064

1
Ca++
2

59
...
00062

NO 3

71
...
00074

1
Mg++
2

53
...
00055

HCO 3

44
...
00046

Na+

50
...
00052

CH 3COO

40
...
00042

ht
tp
:/
/k
er
al
a

K+

te

H+

no

Ionic Conductance and Ionic Mobilities of some Ions at Infinite Dilution at 25°C
...
This regularity was first observed by Kohlrausch and was put in the form of
a law which is known as Kohlrauschs law
...
e
...

λ∞ = Ionic conductance of anion
...
blogspot
...
PM5

215

sp

215

ELECTROCHEMISTRY

...

bl

Highlight:
Kohlrauschs law can be stated in another way: At infinite dilution, when the
dissociation of an electrolyte is considered complete, each ion makes a definite
contribution towards the molar conductance of the electrolyte irrespective of its
∞
association with other ions
...
λ∞ + r
...
4 ohm1
Na+ = 50
...
22 ohm 1
K
Cl = 76
...
40 ohm1
NO3 = 71
...
Examples are: λm (KCl) = λK

ch

no

lo

gi

ca

Applications of Kohlrauschs law
(i) Determination of ionic conductances
...
Its unit is ohm1 cm2 and is directly proportional to the
speeds of the ions
...

And
λ∞ = λc + λa = ku + kv = k(u + v)
λc
u
kv
∴
=
=
= t+
u+ v
λ ∞ k(u + v)

λa

kv
v
=
= t = (1 t+)
λ ∞ k(u + v) u + v
So, the ionic conductances of cations and anions can be determined from their
experimentally determined transport numbers from the above relations
...
But λ∞ for weak electrolytes can be calculated from
Kohlrauschs law
...

Calculate λ∞ for CH3COOH
...

So, ( λ + + λ
+ λ H + + λ Cl − ) ( λ Na + + λ Cl ) = (x + y z) = (λ CH 3COO − + λ H + )
Na
CH 3COO
λ∞(CH3COOH)
(iii) Ionic mobility (Absolute velocity of ions)
We have,
It 1000

...
blogspot
...
PM5

216

...

bl

h = The distance through which cation moves
...

C = Concentration (equiv
...

1
1
=
=I
ρ V /I

ve

Specific conductance K =

rs

when, A = 1, Potential gradient = 1 V cm1

[3 V = 1 V cm1]

1
λ
= c
F
F

d i

[3 t+ λ∞ = λc]

λa
, where V = mobility of anion in cm sec1 under potential gradient
F

ch

1 V cm1
...

Highlights:

• The ions move very slowly
...

• The H+ ions are about five times and OH ions are three times faster
...
And
the use of this conductivity change is made to determine the equivalent point of reactions
involving neutralisation reactions or precipitations
...
And the end point is determined
...
9
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH9-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

218

y
...

ve

rs

it

• Measurements of conductance in the region of equivalence point are of little value
due to hydrolysis, dissociation or solubility of the reaction products
...
9
...

lo

gi

ca

lu

ni

(a) Neutralisation Reactions
In the titration of a strong acid with a strong base, there is always an initial decrease in
conductance
...
In the titration of
NaOH with HCl, the decrease in conductance is due to the replacement of OH ions (molar
ionic conductivity = 199) by Cl ions (molar ionic conductivity = 76)
...

In the titration of HCl with NaOH, the initial fall in conductance is due to the replacement
of H+ ions (350) with Na+ ions (50) and the rise beyond equivalence point is due to excess OH
ions (199) [Fig
...
10(a)]
...
9
...

Conductivity rises
due to excess
H+ (aq) ions added

Conductivity of
Na+Cl– (aq)

End point

Volume of HCl (aq) added

Fig
...
10 (a) Changes in conductivity during titration
of NaOH(aq) with HCl(aq)
...

Conductance

Conductivity

ht
tp
:/
/k
er
al
a

te

Conductivity falls as
OH– (aq) ions are
neutralized

Volume of alkali

Fig
...
10 (b) Changes in conductivity
during titration of a weak acid
(CH3COOH) (aq) with a strong
base (NaOH) (aq)
...
The precipitate should be formed fairly rapidly and should not have
strong adsorbent properties
...
The nature of the titration curve is as in Fig
...
10 (c)
...
So, end point of the reaction can be
determined easily
...
blogspot
...
PM5

218

...

bl

og

sp

219

ELECTROCHEMISTRY

ni

Volume of AgNO3

Fig
...
10 (c) Titration curve of KCl solution by AgNO3 solution
...
The conductance increases as the concentration of the
salt increases
...
9
...
The equivalence point is located by extrapolating the
straight lines
...

ch

no

Example 1
...
25 cm2
...
5 cm
...
If the cell is filled with an electrolyte and offers a resistance of 1996 ohm,
calculate the cell constant and specific conductivity
...
5
=
= 8
...
25

1
ohm1
...

Observed conductivity =
Specific conductivity

1
1
= 8
...
2 × 103 ohm1 cm1
...
4 ×

N
KCl solution at 25°C is 0
...

50
If the resistance of cell containing this solution is 500 ohms, what is the cell constant?
Example 2
...

Cell constant =

or

l
a

and

R=ρ

l
a

1
R
l
=
=R×
=R×K
ρ
ρ
a

l
= 500 × 0
...
138 cm1
...
blogspot
...
PM5

219

...

y
...
Specific conductivity of a conductivity cell containing 0
...
767 ×
103 ohm1 cm1, the observed resistance of the cell is 4364 ohm
...
If
the cell is filled with another solution the observed resistance is 3050 ohm
...

ve

rs

R
1
l
=
=R×
=R×K
a
ρ
ρ

or

3050
R
=
ohm
...

12
...
58 ohm
...

lu

ρ=

ni

l
= R × K = 4364 × 2
...
075 cm1
a

∴

no

Sol
...
A conductivity cell containing 0
...
The specific conductivity of 0
...
002768 ohm1 cm1
...
2 N ZnSO4 , the observed resistance of the
cell is 72
...
Calculate the equivalent and molar conductivities of the ZnSO4 solution
...
002768 = 1
...
5224 ×

ht
tp
:/
/k
er
al
a

te

ch

Again,

1
= 0
...
18

λv(equivalent conductivity) = Kv ×

1000
C

1000
0
...
45 ohm1 cm2

= 0
...
02109
=
M
0
...

= 210
...
The resistance of a decinormal solution of a salt occupying a volume between
two Pt electrodes 1
...
4 cm2 in area was found to be 32 ohms
...

Sol
...

×
=
=
R a
32 5
...
010416 ohm1 cm2
λv =

1000 K
1000 × 0
...
166 ohm1 cm2
...
1

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH9-1
...
c
ot
og

Example 6
...
028 × 103 (N) acetic acid is 48
...
Its equivalent conductance at infinite dilution is 390
...

Calculate the degree of dissociation of acetic acid
...
15
= 0
...

390
...

y
...

rs

Example 7
...
1 λ∞AcONa = 91
...
5
...

λ∞HCl + λ∞AcONa λ∝NaCl

ve

given:

sp

221

ELECTROCHEMISTRY

= λ H+ + λ OAc = λ∝AcOH

ni

= (λ H + + λ Cl ) + (λ Na + + λ OAc ) − (λ Na + + λ Cl )

lu

∴ 426
...
0 126
...
6 Ohm1 cm2
...
Equivalent conductance of acetic acid at 25°C is 0
...
If
ionic conductance of H+ ions and CH3COO ions at infinite dilution are 0
...
004 ohm1 m2eq1, respectively
...

λ∞(CH3COOH) = λ∞H+ + λ∞CH3COO

Sol
...
0348 + 0
...
0388

λ∞

=

0
...
046
...
0388

te

ch

Example 9
...
Calculate the percentage ionisation of acetic acid
...
8 × 105)
...
Strength of CH3COOH solution =
Initially

CH3COOH
= 0
...
05(1 α)

∴

Ka =

3
g equiv
...
05(N)
60
CH3COO + H+
0
0
α

...
05α

0
...
05α
[CH3 COO ] [H + ]
(0
...
05 (1 α)
[CH 3COOH]
0
...
05α2
α=

Ka
=
0
...
8 × 10 −5
=
0
...
9 × 103
0
...
01898
...
The specific conductivity of saturated solution of AgCl is 1
...
The mobilities of Ag+ and Cl ions are 53
...
3 mho eq1 cm2
...
wt, Ag = 108, Cl = 35
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH9-1
...
c
ot
og

ENGINEERING CHEMISTRY

Sol
...
3 + 65
...
1 mhos eq1 cm2
λv = KvV
119
...
6 × 105 cm3 eq1
Kv
1
...
6 × 102 l eq1

rs

V=

1
eq l1 = 0
...
6 × 10 2
= (0
...
5) g l1

=

ni

∴ Solubility

ve

∴

it

y
...
e
...
916
=
v 1
...
916
0
...
478
u + v 0
...
916

lo

Speed of NO 3

gi

Speed of Ag +

ca

lu

= 0
...

Example 11
...
916
...

Sol
...
478 = 0
...

te

ch

Example 12
...
The amount
of Cu in the anodic solution was found to be 0
...
6236 g before and after electrolysis,
respectively
...
1351 g
...

Wt
...
of Cu from anodic solution (anolyte)

= 0
...

= (0
...
6236) g = 0
...
Wt
...
wts
...
88), Cu(63
...
6236 g
...
of Ag deposited in voltameter
= 0
...

∴ Amt
...
1351 g of Ag
...
of Cu( x)
wt
...
wt
...
wt
...
1351
x
=
63
...
88
2

0
...
8
= 0
...
88

∴

x=

∴

tCu +2 =

∴

∞
tSO4 = 1 tCu +2 = 1 0
...
714
...
114
=
= 0
...
0398

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH9-2
...
c
ot
og
bl

SHORT QUESTIONS AND ANSWERS

y
...
1
...
Electrochemistry is the study of interrelations of electrical energy and chemical
energy and interconversions of the two energies
...
m
...
of a cell as well as electrolysis
...
2
...
Electrochemical reactions are the reactions which involve the flow of current
...
3
...

ni

Ans
...
e
...

ca

(ii) Electrochemical cell reactions: Electrochemical cell reactions are mainly redox
reactions, involved in the cell where electrical energy is produced due to a chemical change
...
4
...
Electrolysis is a process where electric current is used to decompose a molten ionic
compound or a solution of ions into elements
...
5
...
Ions can only conduct electricity when they are free to move, which is only possible
in molten state or in solution
...
6
...

Ans
...

ht
tp
:/
/k
er
al
a

(ii) Electrolysis of brine to produce NaOH and Cl2

(iii) Electroplating
(iv) Copper refining
...
7
...
Metals are deposited at the cathode and the nonmetals are liberated at the anode
...
8
...
During electrolysis of a solution of a salt in water, the deposition at the cathode
depends on the type of metal ion in the salt
...
Cu+2
Cu+2(aq) + 2e

Cu°(s)

But if the metal is in higher position in electrochemical series, the product at the cathode
is hydrogen, from hydrogen ions produced by the ionisation of water
2H+ (aq) + 2e

H2(g)

During the electrolysis of a salt solution, the liberation at the anode depends on the type
of electrode
...
blogspot
...
PM5

223

sp

223

ELECTROCHEMISTRY

...
If the anode is a metal (Cu, or Ag), atoms of
electrode turn into ions
...

Cu(s) → Cu2+ (aq) + 2e
...
9
...
The concentration of a salt solution has an effect on the product of electrolysis at
the anode
...
In electrolysis of a dilute solution of NaCl increasing amounts of oxygen are liberated
...
10
...

ni

(b) Sodium is extracted by the electrolysis of a mixture of a molten NaCl
and CaCl2
...
What mass of
Na is formed in an hour at the steel cathode?

lu

Ans
...
9
...
Electrolytic cell
...

Quantity of electricity in an hour = 30000 C/S × 3600 s
...

Amount of Na formed per hr
...
75 kg
...
11
...
Electrolysis of brine is the basis of the alkali and chlorine industrya well known
electrochemical industry
...
Electrolysis of brine is used
to manufacture chlorine, hydrogen and sodium hydroxide
...

Mass of Na formed per hr
...
blogspot
...
PM5

224

...

bl

The cell to be used for electrolysis should be carefully designed so that chlorine can be
kept apart from NaOH, otherwise they will react
...

H2(g)

it

Cl2(g)

–
Ni-electrode

ca

+
Ti-electrode

Porous
membrane

NaOH(aq)

lu

ni

ve

rs

Brine

gi

Fig
...
12 Membrane cell
...
9
...
The membrane permits the solution to pass and
prevents mixing of NaOH and Cl2
...

no

Q
...
What do you mean by resistance?

ch

Ans
...

te

R∝

l
; where l = length, a = area of cross-section of the conductor
a

l
a
where, ρ = proportionality constant and is known as specific resistance or resistivity
...
a
; unit of R = ohms
...
13
...
Specific resistance or resistivity is the resistance offered by the conductor of 1 cm
length and 1 cm2 area of cross-section
...

R
...

unit of ρ = ohm-cm
...
14
...
The conductance (C) is the reciprocal of R
1
C=
R
Unit of conductance = ohm1 or mho

From,

ρ=

It is a measure of ease with which current flows through a conductor
...
blogspot
...
PM5

225

...

K=

bl

Q
...
What is specific conductance?
Ans
...

og

ENGINEERING CHEMISTRY

ve

rs

it

It is defined as the conductance of 1 cm3 of a conductor
unit of K = ohm1 cm1
Q
...
What do you mean by equivalent conductivity of an electrolytic solution?
Ans
...

1000 K
C
C = normality of the solution
...

Q
...
What do you mean by molar conductivity of an electrolyte?
Ans
...
i
...
, molar conductivity λm =
M
where, M = molarity of the solution
K = specific conductance
...
18
...

Ans
...

Q
...
What is the effect of dilution on molar conductivity?
Ans
...

Q
...
What do you mean by degree of dissociation of an electrolyte?
Ans
...
For weak electrolytes it is related to λm and λm∞ as follows:
λ
α= m
...
21
...
It is the fraction of total quantity of electricity, carried by cations or anions
...
22
...

Ans
...

Q
...
What are the applications of conductance measurement?
Ans
...

(ii) Determination of solubility and solubility product
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH9-2
...
c
ot
og

sp

227

ELECTROCHEMISTRY

Q
...
All conductance measurements are done with the help of A
...
explain
...

bl

Ans
...
C
...

Q
...
In all conductometric titrations, we plot conductance vs
...

FG
H

rs

Ans
...
volume will not give straight
line
...

ni

Q
...
Equivalent conductivity of a weak electrolyte increases with dilution
explain
...
Equivalent conductivity of a weak electrolyte depends on the number of ions of
the electrolyte present in solution with dilution of a weak electrolyte, degree of dissociation
increases, so is the number of ions
...

lo

gi

Q
...
Why equivalent conductivity at infinite dilution cannot be directly
determined experimentally?

ch

no

Ans
...
e
...

λ = λ∞ K c

cm eq

–1
0

150

Equivalent conductivity-L-ohm

–1

ht
tp
:/
/k
er
al
a

te

So, λ∞ can be determined by extrapolation of the curve λ vs
...
9
...
However λ are not so related in case for weak electrolytes
...

Sodium chloride
100

Sodium acetate
50

Acetic acid
0

–4
–8
ÖC – (C in equivalent/liter)

Fig
...
13 Extrapolation of λ versus

?
...
blogspot
...
PM5

227

...
28
...

rs

it

y
...
When an electrolyte is diluted, degree of dissociation increases and also the total
volume increases
...
But it outweighs the
minor increase in conductance due to increase in degree of dissociation
...
e
...
But equivalent conductance increases because the total number of
ions per gram equivalent increases with dilution for the increased value of degree of dissociation
...
What do you mean by electrolysis?

2
...
C
...

(b) Relate C
...
and E
...
E
...

E1 E2
E
=
=
...

Zn
Z1 Z2

gi

(b) Prove that

ca

(a) State the Faradays laws of electrolysis
...

lu

1
...

(a) Define the terms (i) specific conductance and (ii) equivalent conductance
...

ch

5
...

What is meant by the transport number of an ion? How is it determined? A molar solution of
CdI2 showed an anion transport number 1
...
How would you account for the result?

ht
tp
:/
/k
er
al
a

6
...

7
...
Mention its units
...
Discuss its significance and applications
...

(a) Define transport number
...

(c) State Kohlrauschs law
...

9
...

(b) Define specific conductance
...

(d) Define Faradays second law
...

10
...

(b) State Kohlrauschs experimental equation
...

11
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH9-2
...
c
ot
og

sp

229

ELECTROCHEMISTRY

rs

it

y
...
Write short notes on :
(i) Cell constant
(ii) Absolute velocity of an ion
(iii) Conductometric titration
(iv) Kohlrauschs extrapolation method of determining λv
...
Discuss all types of conductometric titrations
...

14
...

15
...
000275 mhos cm1
...
0
...
098 (N) KCl was found to be 214
...
Calculate the equivalent
conductance (λv) of the solution at the same temperature, if the cell constant is 0
...

[Ans
...
18 ohm1 cm 1]
The resistance of a conductivity cell filled with 0
...

Calculate the equivalent conductance (λv) of the solution (cell constant = 0
...

[Ans
...
9 ohm1 cm2]
The resistance of a cell filled with 0
...
The specific conductance of 0
...
00277 ohm1 cm1
...
1 M of CuSO4 ; and its resistance was found to be 37
...
Calculate
the equivalent and molar conductances of CuSO4 solution
...
83
...
0 ohm1 cm 2]
The resistances of 0
...
02 N of an electrolytic solution in a conductivity cell
were found to be 310 ohms and 2,000 ohms respectively at 298 K
...
1 N KCl solution is 0
...
Calculate the equivalent conductance of the
given solution
...
99
...
74 × 104,
144
...
36 × 104 Sm2 eq1 respectively
...

[Ans
...
382 × 102 S m 2 eq1]
1 cm2 eq1
...
01 N acetic acid is 16
...
What is
the percentage dissociation of acetic acid at this concentration?
[Ans
...
19%]
During the electrolysis of CuSO4 solution, loss of Cu in the anode compartment was 0
...
In a
voltameter connected in series, 1
...
Find the transport no
...

lu

ht
tp
:/
/k
er
al
a

21
...

no

lo

19
...

gi

17
...
Specific conductivity of an

22
...

[Ans
...
215]

24
...
84% CuSO4 solution was electrolysed using Pt cathode and Cu-anode
...
409 g Cu in 54
...
The increase in the weight of cathode

was 0
...
Calculate the transport number of Cu+2 and SO 4 ions [At
...
= Cu(63
...

[Ans
...
215, tSO = = 0
...
A 0
...
After electrolysis 51
...
519 g of AgNO3
...
current was passed for
[Ans
...
46]
2 mins
...
of Ag+ in AgNO3
...
blogspot
...
PM5

229

...

10

ve

rs

Electrochemical Cells

ni

ELECTRODE POTENTIAL

ht
tp
:/
/k
er
al
a

te

ch

no

lo

gi

ca

lu

Oxidation is a process where electrons are lost by a substance and reduction
is a process where electrons are gained by a substance
...
e
...
85 g
...
atom of Fe
to 1 g
...
And for every g
...

If we make an arrangement as shown in Fig
...
1 after sometime, we get Sn+4 in the
vessel B and Fe+2 in vessel A
...
There is a clear sign of
flow of electrons through the metallic wire connected and this arrangement is considered as a
cell which generates electric current at the cost of oxidation and reduction reactions occurring
simultaneously
...
m
...
of the cell
...
10
...

2Fe+3 + 2e
Sn+2 2e

Fe+2 [reduction]
Sn+4 [oxidation]

2Fe+3 + Sn+2
Fe+2 + Sn+4 [cell reaction]
So, a cell is constructed of two electrodes and the e
...
f
...

Nernst Solution Pressure Theory for Electrode Potential
If a metal rod (M) is dipped into a solution containing its ions (M+n) the metal shows a
tendency to send ions into solution
...
By
230
http://keralatechnologicaluniversity
...
com

...

bl

sending the ions, the metal rod accumulates electrons and as a result, metal rod becomes
negatively charged
...
When solution pressure equalises osmotic pressure there is
no net effect
...
As for
example, in the case of Zn/Zn+2, the solution pressure
Zn
Cu
exceeds osmotic pressure, Zn rod sends Zn+2 ions into
+ – – +
the solution and gets negatively charged and attracts
– + + –
+ – – +
– + + –
positive charges towards the rod and, as a result, an
+ – – +
– + + –
+ – – +
electrical double layer is set up and a potential is
CuSO4
ZnSO4
established between the metal rod (Zn) and its ions
(Zn+2)
...
10
...

osmotic pressure exceeds solution pressure and Cu rod
gets positively charged
...
This established potential is called
electrode potential
...
For example, the system
(Pt) Fe+3 + e

lo

(Pt) Fe+2

no

sets up an electrical double layer where an inert metal platinum is dipped into a mixture
containing Fe+2 and Fe+3 and an electrode potential is established
...
To consider the electrodes
separately, we call each of them as single electrode
...
E
...
F
...

E = ∈1 + ∈2

ht
tp
:/
/k
er
al
a

Single Electrode Potential (∈)
∈

The electrode potential for an electrode reaction:
M+n + ne
M (metal)

is given by Nernst equation ∈ = ∈° +

metal
...

At 25°C the equation comes to :
∈ = ∈° +
= ∈° +

2
...
341 × 298
log10 aM + n
n × 96500
0
...
blogspot
...
PM5

231

...
059
log10 C + n
M
n

[A form of Nernst equation]

y
...

rs

If we construct the following cell:

ve

Zn()| Zn+2 || Cu+2 |(+) Cu, Ecell = 1
...
e
...
e
...

ca

Total cell reaction is:

Zn+2 + Cu
...

ch

• The double vertical lines denote the junction of the two solutions and this liquid
junction potential is eliminated or minimised by the use of a salt bridge
...
The right hand half cell is regarded as
the positive electrode and the left hand half cell is regarded as negative electrode
...
So reduction takes at the right hand electrode and oxidation takes place
in the left hand electrode
...
m
...
of the cell E = ∈right ∈left (when both are reduction potentials)
E = ∈red + ∈ox
...

Determination of Standard Potential ∈° of a Metal Electrode

The electrode potentials cannot be determined straight
...
For example, to determine the electrode
potential, we take the ∈° value for hydrogen electrode to be zero i
...
, a solution of acid with
([H+] = 1) and to which hydrogen gas is bubbled at one atmosphere and platinum foil is dipped
...
Now if we want to determine standard electrode
potential of zinc (∈°Zn) we are to construct the following cell
...
blogspot
...
PM5

232

sp

232

...
10
...

Electrode
1
2

F2

Pt, O2; H+

1
2

O2 + 2H+ + 2e = H2O

Au, Au+++
Hg, Hg2++
Ag, Ag+
Pt; Fe+++, Fe++
Cu, Cu++

Au+++
Hg2++
Ag+
Fe+++
Cu++

+
+
+
+
+

Calomel electrode

1
2

+ e = Hg + Cl

0
...
000

Hg2Cl2

Pb,
Sn, Sn++
Zn, Zn++
Mg, Mg++
Na, Na+
Li, Li+

Sn++
Zn++
Mg++
Na+
Li+

ca

H+

Pb++

no

lo

gi

Pb++

it

2
...
23

1
...
799
0
...
771
0
...
360

rs

+ e = Cl

Cl2

(Pt) H2, H+

Reductants
i
...
, electropositive

+ e = F

ni

Oxidants
i
...
, electronegative

Pt, Cl2(g);

Cl

lu

F2, F

+ e=
+
+
+
+
+
+

H2

2e = Pb
2e = Sn
2e = Zn
2e = Mg
e = Na
e = Li

0
...
136
0
...
866
2
...
959

ch

The e
...
f
...
m
...
m
...
E° of the
above constructed cell which is ∈°Zn
...
This list with ∈° values are known as electrochemical series
...
1)
Example 1
...
m
...
of the cell

Sol
...
oxidation potential of Zn
...
344 + 0
...
106
...
m
...
of a cell
Liquid junction potential

Daniel cell:

Zn | ZnSO4(C1) || CuSO4(C2) | Cu

Cell reaction is:

Zn + Cu+2

Zn+2 + Cu

E = ∈right ∈left
°
∈right = ∈Cu +

[when both are reduction potentials]

RT
[Cu +2 ]
ln
2F
[Cu]

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH10-1
...
c
ot
[Q [solid] = 1]

RT
ln [Zn +2 ]
2F

y
...

2F
[Zn +2 ]

7
8
9

ni

∴

7 4
8 5
9 6

RT
RT

...
ln [Zn +2 ]
2F
2F

rs

4
5
6

°
Ecell = ∈Cu +

[Q [solid] = 1]

ve

∈left = ∈°Zn +

Interpretation of the Electrochemical Series (Table 10
...
The higher the standard electrode potential (reduction) of an element, higher is the
electronegativity of that element
...

gi

2
...
m
...
of the
cell is obtained from the oxidation potential of anode and reduction potential of cathode
...
m
...
of the cell,

no

E = Reduction potential of Cu + Oxidation potential of Fe
...
344 + 0
...
785 volt
...
The higher electropositive metal i
...
, possessing lower standard electrode potential
(reduction) will displace the metal from the solution of its ions with a higher standard electrode
potential (reduction) value
...
762) will displace Cu from its solution (∈°Cu =
...

For example:
2KI + Cl2 → 2KCl + I2↑

Redox-electrodes
A mixture of Fe+2/Fe+3 salt in a solution or Ce+3/Ce+4 salt in a solution can act as an
electrode if a platinum wire is dipped into either of the solutions
...
These electrodes are known as redox electrodes
...

a
RT
0
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH10-1
...
c
ot
og
bl

Table 10
...
15
0
...
36
0
...
535
+ 0
...
20
+ 1
...
25
+ 1
...
36
+ 1
...
52

Ce+4

Ce+2

+e
MnO4 + 4H+ + 3e
MnO2 + 2H 2O
CO+2 + e
CO+2
S2O42 + 2e
2SO42

+
+
+
+

1
2

te

F2/F

ht
tp
:/
/k
er
al
a

1
2

ch

Ce+4/Ce+3

1I
2 2

+
+
+
+

+ 1
...
00

Sn+2
Cu+1
Fe(CN)64
MnO42

lu

(Pt) Fe+2/Fe+2

H2

ve

Sn+4/Sn+2
Cu+2/Cu+1
[Fe(CN)6]2/[Fe(CN)4]4
MnO4/MnO42

ni

(Pt)
(Pt)
(Pt)
(Pt)

0
...
21 0
...

Electrode

F

+ 2
...
61
1
...
82
2
...

Latimer Diagram

The redox potential of different oxidation states for a particular element can be
summarised with the help of EMF diagram and the simplest type of such diagram is the Latimer
diagram
...

We know that Mn exists in different oxidation states and in acidic medium preferably at
zero pH, the different oxidation states are represented by the corresponding ∈° values as
follows:
Mn2+ + 2e +
Mn,
∈° = 1
...
52 V
MnO2 + 4H+ + e
Mn3+ + 2H2O,
∈° =
...
26 V
MnO42 ,
∈° = +
...
23 V
2

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH10-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

236

0
...
26 V

0
...

bl

MnO4 + 4H+ + 3e
MnO2 + 2H2O, ∈° = 1
...
51 V
The whole information can be summarised in the compact manner in a collinear diagram
as follows
...
52 V

1
...
The
species H+, H2O etc
...
The couple such as MnO4/MnO2 or
MnO4/Mn2+ or MnO2/Mn2+ etc
...

A Latimer diagram helps us to derive the standard potentials of such non-adjacent
couples
...
Again ∆G° is related to ∈° as follows, ∆G° = nF∈°
...
Since the nF factor
cancels in this way, we can write
n1∈°1→ 2 + n2 ∈°2 → 3
∈°1 → 3 =
n1 + n2

ht
tp
:/
/k
er
al
a

te

ch

no

lo

Besides calculating the ∈° values of non-adjacent couples, the Latimer diagram is also
helpful in predicting whether a particular species will undergo disproportionation or
comproportionation
...
On the other hand, a species will undergo
comproportionation if the potential on the left is higher than that of the right species in the
diagram
...

0
...
76 volt

O 2 → H 2 O 2 −1 → H 2 O −2

The feasibility of disproportionation of H2O2 can be predicted by considering the
change in the ∈° values for the following reactions:
Overall reaction:
2H2O2 → 2H2O + O2
(a)
∴

(b)
∴

H2O2 → O2 + 2H+ + 2e

Oxidation:
Reduction:

∈°Ox =
...
70) = 1
...
76 V
∆G°2 = nF∈° = 2F × 1
...
52 F

Adding (a) and (b),
2H2O2 → 2H2O + O2
∆G° = 2
...
80 V

1
...
On the other hand, for the change Ag2+ → Ag+ → Ag
it can be shown by similar calculation that disproportionation of Ag+ will not take place because
it will be accompanied by increase in ∆G° value
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH10-1
...
c
ot
og

Frost Diagram

ni

ve

rs

it

y
...
On the basis
of this diagram, it can be predicted whether the oxidant or the reductant will show greater
tendency for a reaction
...
Hence, we can make thermodynamic predictions
about the reaction between any two couples by comparing the steps of the corresponding lines
...

The reducing agent of the couple with less +ve slope will tend to undergo oxidation
...
10
...
3(b)
...
10
...
10
...

An examination of this plot shows that the slope of the line connecting HNO3 to lower
oxidation numbers is quite steep and hence HNO3 will function as a good oxidising agent
under standard conditions i
...
, (at pH = 0)
...
The diagram also indicates that the slope remains steep all the way to N2
indicating that N2 should be the product of reduction of HNO3 if excess Cu is present in the
reaction
...

An ion or a molecule in a Frost diagram will be unstable with respect to disproportionation
if it lies above the line connecting two adjacent species
...
From the diagram it is seen that since NH2OH lies above the line joining NH3 and N2
it will undergo disproportionation
...

A substance that lies below the line connecting two adjacent neighbours in a Frost
diagram is more stable than they are because its average free energy is lower
...
g
...
blogspot
...
PM5

237

...

bl

other hand N2O has an oxidation state of +1, which is intermediate between 3 and + 5 and its

position in the Frost diagram is lower than that of NO3 ion and NH4+ ion and so NH4NO3
+ + NO → N O + 2H O
...
g
...
This is due to the fact that NO, HNO2
and HNO3 lie approximately on a straight line in the Frost diagram
...
g
...

0
...
76 V

H2O2

ca

O2

H2O

gi

+1
...

When O changes from O2 to H2O2, oxidation number of O changes from 0 to 1, Hence,
change in oxidation number = 1
...
70 =
...
Therefore, n∈° for the formation
of H2O = 2 × 1
...
46 volt
...

ht
tp
:/
/k
er
al
a

te

The potential corresponding to reduction of H2O2 to H2O can be calculated as follows
from the examination of the line it is obvious that at the point corresponding to 1 oxidation
number n∈° =
...
46 volt
...
46 (
...
76 volt
...
Therefore, the ∈° for the couple

− 1
...
76 volt
...
10
...

This is in accordance with the Latimer diagram
...
blogspot
...
PM5

238

...

1
...

2
...

3
...

bl

Highlights:

Zn + Cu+2

∈° Zn +2 / Zn = 0
...
Predict whether the reaction will occur spontaneously or not
...
344

ni

The two half cell reactions are:

Zn [∈° = 0
...
344]

Zn+2 + Cu

Zn + Cu+2 [E°Cu = 1
...

lu

Zn+2 + 2e
Adding

lo

So, the reaction will not occur spontaneously
...
Find whether Cu+ disproportionate in aqueous solution into Cu+2 and Cu°
i
...
, cell reaction is

ch

2Cu+

Cu+2 + Cu°, Given, ∈° Cu +2 /Cu + = + 0
...
52 V

ht
tp
:/
/k
er
al
a

The two half cell reactions are:

Adding

Cu+2

sp

239

ELECTROCHEMICAL CELLS

Cu+ + e

Cu° [∈° = 0
...
15 V]

e

Cu+ + Cu+

Cu+2 + Cu° [E°cell = 0
...

Example
...
798
...
Cell reaction:

2Ag + 2H+ → 2Ag+ + H2

The two half cell reactions are:

Adding

2Ag 2e

2 Ag+ [∈° = 0
...
00 V]

2Ag + 2H+

2Ag+ + H2 [E°cell = 0
...

Concentration Cell
When a metal is dipped into two solutions of one of its salts of different concentrations,
a very interesting situation arises:

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH10-1
...
c
ot
og

ENGINEERING CHEMISTRY

AgNO3(C2)
[Concentrated]

Ag | AgNO3(C1M) || AgNO3(C2M) | Ag

(C2 > C1)

ve

rs

Voltmeter

–

NH4NO3
Salt bridge

ni

e

ca
gi

+

no

+

ch

C1M Ag ions

Ag
electrode

+

Ag + e–® Ag

lo

Ag ® Ag + e –

Electron
flow

+

lu

–
Ag
electrode

Ag

y
...

NH4NO3

it

AgNO3(C1)
(Dilute)

bl

Ag | AgNO3(C1) || AgNO3(C2) | Ag
Ag

+

C2M Ag ions

C2 > C1

Fig
...
5 Concentration cell
...
We shall
get silver deposited on the right hand electrode and dissolution of silver from the left hand
electrode as if silver being transported from concentration C2 to concentration C1
...
303
E=

2
...
138 × (298)
RT
C
C
log 2 =
log 2
C1
C1
nF
n × 96500

0
...
m
...
of such cell depends on the relative concentration and not on the absolute
values
...
m
...
is 59 mV
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH10-1
...
c
ot
og

This type of concentration cell is known as electrolyte concentration cell
...

bl

Another type of concentration cell is electrode concentration cell, one such cell is:
Pt | H2 (p1) | H+ | H2 (p2) | pt

2H+
H2 (p2)

H2 (p1) 2e
2H+ + 2e

H2(p1) → H2(p2)

Application of the Concentration Cells H2

lu

Determination of solubility of sparingly-soluble salts
...
m
...
of the following

ca

cell
...

2

e
...
f
...
01N)
Saturated AgCl | Ag
salt bridge
C
0
...
m
...
of the cell is given by,

ch

E=

te

Here n = 1, concentration of Ag+ in 0
...
01 g
...

So,

E=

0
...
01
log
1
C1

ht
tp
:/
/k
er
al
a

So, C1 i
...
, Ag+ in AgCl can be calculated
...
Calculate (i) Solubility product of AgI, (ii) Solubility of AgI in water at 25°
...
m
...
of the cell is 0
...
The activity coefficient (f) is 0
...

Cell: Ag/AgI/ in 0
...
05M) | Ag
...
05 × 0
...
045 M
The concentration of I in KI is 0
...
9 = 0
...

∴

or
or
or

E=

0
...
045
log
1
C1

0
...
059 log

log

0
...
045 0
...
33
C1
0
...
045
= Antilog 13
...
138 × 1013

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH10-1
...
c
ot
K sp

rs

Solubility of AgI =

bl

Ksp

y
...
045

= 2
...

2
...
105 × 1015 × 0
...
472 × 1017
C1 =

it

∴

og

ENGINEERING CHEMISTRY

lu

ni

ve

−
= 9
...
732 × 109 mol l1
= 9
...
5 g l1
= 1
...
5(N) || Hg2(NO3)2 (0
...
m
...
of the above cell = 0
...
059
0
...
5
log 2 =
log
We have,
E=
where n is valency
...
05
0
...
059
log 10 =
=
n
n
0
...
059
0
...

n
0
...
The
platinum black surface exhibits a strong absorption power
towards hydrogen gas, as a result, the metal surface remains
in continuous contact with the hydrogen gas
...
When
in use, therefore, only a part of the foil is immersed in 1(N)
HCl; the remainder is surrounded by pure hydrogen gas at
1 atm
...
This is standard hydrogen electrode
...
m
...
of this electrode has been arbitrarily assigned to be zero
...

H2-Gas

HCl

Fig
...
6 Hydrogen Electrode
...
blogspot
...
PM5

242

sp

242

...
059 log [H+]
= 0
...

∈ = ∈° + 0
...

RT
[H 2 ]1/ 2
log
F
[H + ]

rs

∈ = ∈° +

ni

ve

A full cell is constructed by coupling the above half cell with a standard hydrogen
electrode
...
m
...
E of the cell is then determined potentiometrically
...
m
...
of the cell gives directly the electrode
potential (∈) of the half cell
...
059

lo

pH =

ca

EObs = ∈ = 0
...

KCl

+

HgCl
paste

H2

Calomel
electrode

Solution

Salt bridge
Hydrogen
electrode

Fig
...
7 Determination of pH by Hydrogen Electrode
...
But there are some difficulties with hydrogen electrode
...

pressure of hydrogen and to make aH+ = 1 is very difficult
...
One of such electrodes is calomel electrode
...
10
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH10-1
...
c
ot
og

ENGINEERING CHEMISTRY

Calomel Electrode

ni

ve

rs

it

y
...
It can be prepared easily and can be used
for a long time
...

gi

ca

lu

KCl

HgCl + Hg
Hg

lo

Fig
...
8 Calomel Electrode
...
Mercury layer is covered with a paste
of Hg2Cl2 (0
...
The
electrode reaction is:
1
Hg + Cl ( aCl − )
Hg 2 Cl 2 (s)
2
The electrode potential ∈ is given by

RT
ln aCl − ( Q n = 1)
...
0(N) KCl = + 0
...
2422 V
Any electrode whose standard potential is to be determined is connected to calomel
electrode by means of KCl salt bridge
...
m
...
of the set-up cell is determined
potentiometrically from which the standard electrode potential of the electrode is calculated
...
059 log [H+]
= 0
...
059 pH

ht
tp
:/
/k
er
al
a

sp

244

∈ = ∈° +

or

pH =

E Obs − 0
...
059

Ag-AgCl Electrode
The use of this reference electrode is very common
...
The potential of this electrode

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH10-2
...
c
ot
og
bl

Ag/AgCl(s) Cl ( aCl − = 1) || HCl (a = 1), H2 (1 atm)/Pt
∈° = 0
...

has been accurately determined against a standard hydrogen electrode
...
The thick glass
membrane serves as a solid electrode whose potential changes with pH of the solution with
which it remains in contact
...
A platinum wire may be used in place of the
AgAgCl electrode (Fig
...
9)
...
The potential of the glass electrode varies
linearly with pH (Fig
...
10)
...
303 RT
pH
F
= ∈° 0
...

te

ch

no

= ∈°

+

ht
tp
:/
/k
er
al
a

–
Potentiometer

Pt wire or
silver chloride
coated silver
wire

Saturated
calomel electrode
Glass
electrode

0
...
10
...

Fig
...
10 Determination of pH by Glass Electrode
...
blogspot
...
PM5

245

sp

245

ELECTROCHEMICAL CELLS

...

• e
...
f
...
059 pH
• Glass electrode is virtually hydrogen electrode
...

• ∈° value of glass electrode can easily be determined by calibration using buffers of
known pH
...

lu

ni

ve

The advantages of glass electrode
...

The disadvantages of glass electrode
...

Only lithium silica glasses enable pH measurements to be valid over practically
the entire pH range
...
m
...
of a cell (E) constructed of a reference electrode and an indicator electrode
...
0592 pH
∆E
i
...
,
= 0
...
059
...

Polarisation

sp

246

ht
tp
:/
/k
er
al
a

When a simple cell drives a current, the following is the cell reaction:
At Copper plate:
Cu+2 + 2e
Cu
2H+ + 2e
H2↑
At Zinc plate:
Zn
Zn+2 + 2e
+2 + SO 2
ZnSO4
Zn
4
Total cell reaction:
Zn + H2SO4 = ZnSO4 + H2

+

–
Zn

Cu

dil
...
10
...
blogspot
...
PM5

246

...

bl

When current flows from Cu-plate to Zn-plate, a layer of hydrogen bubbles is found to be
formed on the surface of the Cu-plate
...

(ii) The layer of H2 in contact with the acid solution is found to acquire a potential lower
than that of Zn
...
m
...
is generated, which is called
polarisation e
...
f
...
m
...
and which tends to drive a current opposite to
the direction of the main current flow; and hence this back e
...
f
...
m
...
As the hydrogen bubble is generated more and more, the polarisation e
...
f
...
m
...
and the current
stops totally
...

Polarisation effect is also seen during electrolysis: when an electric current is passed
through dil
...

H2SO4
2H+ + SO42
2 + H O
SO4
H2SO4 + O2
2
At anode: The reaction is,
2O2 4e
O2↑
At cathode: The reaction is,
2H+ + 2e
H2↑
If, after some time, the battery is removed and a galvanometer is fitted in the outer
circuit, a current is seen to pass between the two electrodes, but in opposite direction to that
during electrolysis
...
m
...
(back e
...
f
...
m
...
developed by products
of electrolysis is known as polarisation (Fig
...
12)
...
H2SO4

(a) Polarisation during
electrolysis

(b) Polarised cell

Fig
...
12 Development of polarisation by the products of electrolysis
...
H2SO4 using Pt electrodes applying an e
...
f
...
m
...
developed during electrolysis
...
m
...
which can overcome the effect of back e
...
f
...
m
...
or polarisation
e
...
f
...
10
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH10-2
...
c
ot
it

Current density

y
...
10
...

ni

At this stage, if the applied e
...
f
...
So, a minimum voltage must always be applied to start the electrolysis process
...

• The decomposition potential of CuSO4 is 1
...
55 V with Zn-electrodes
...
m
...
of less than 2-5 V is applied
between Cu-electrodes only Cu will get deposited at the cathode while Zn will
remain in solution if a mixture of CuSO4 and ZnSO4 is used as electrolyte
...
m
...
of the reversible cell constructed with H2 (g) at 1 atm
...
m
...
is always higher than this theoretical value
...
H2SO4 with Ptelectrodes requires 1
...
23 V (theoretical value)
...

Cells are devices where electric current is generated at the cost of some physicochemical
processes going inside the cell
...
Because the thermodynamic principle is only applicable to reversible cells
...
Since electrical
work is equal to nFE, where F = faraday and E = e
...
f
...
Battery works on the above thermodynamic principle
...
blogspot
...
PM5

248

...

bl

(a) Leclanche cell
...
10
...
The
cell consists of a glass vessel B, which contains a saturated solution of NH4Cl as an active
liquid
...
The
anode is made of gas carbon (C) placed within a porous pot P which is also dipped partially in
NH4Cl solution
...
Since MnO2 is a very poor conductor,
charcoal is added to increase the conductivity
...
The seal
has a hole to allow the escape of NH3 gas
...
m
...
of the cell is 1
...

Pitch
+

ni

Hole C
P

ca

lu

Zn

–

gi

Porous pot

Zinc rod(–)

NH4Cl (Sol)

no

te

ch

Carbon–
manganese
dioxide mixture

lo

Carbon rod

Glass vessel

B

ht
tp
:/
/k
er
al
a

Fig
...
14 Leclanche cell
...

When current is drawn from the cell, Zn
rod is used up and the MnO2 is reduced
...

Hole

Pitch

2Mn2O3 + O2 = 4 MnO2

(b) Dry cell
...
10
...
Instead of NH4Cl solution, NH4Cl
paste is used here
...
The cell is not really dry
...

A carbon rod is placed at the centre to act as a
positive electrode
...
The carbon rod is insulated at the bottom
from Zn-vessel with a cardboard washer
...
10
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH10-2
...
c
ot
og

ENGINEERING CHEMISTRY

sp

250

y
...
To prevent drying of the paste, the top of the cell is sealed with pitch
...
The e
...
f
...
45 V
...

it

Alkaline Battery

Zn(s) + 2MnO2(s) + H2O(l) → Zn(OH)2(s) + Mn2O3(s)

ni

Net reaction:

ve

rs

It is a modification of dry cell where NH4Cl has been replaced by KOH and acts as an
electrolyte
...
And
the graphite-rod is kept surrounded by a paste of MnO2
...
The life of alkaline battery is longer than the dry cell because zinc does not
corrode
...
It is mainly used in camera, calculators, watches etc
...
The
cell reaction is
Cd(s) + 2OH(aq) → Cd(OH)2(s) + 2e

Anode:

2NiO
...
OH(s) + Cd(s) + 2H2O(l) → Cd(OH)2(s) + 2Ni(OH)2(s)

ht
tp
:/
/k
er
al
a

te

Here the reaction products adhere to the electrode surfaces and the reaction can be
easily reversed
...
The main advantage of this
battery is that, it undergoes no deterioration as no gases are produced during charging and
discharging
...

Mercury Battery

This type of battery is constructed of zinc-amalgam (a solution of Zn in mercury) as
anode and a paste of KOH, Zn(OH)2 and HgO as cathode
...
The paper permits the migration of ions
...
The size is small
...

Use: It finds its use in pacemakers, hearing aids, digital watches etc
...

Fuel + O2 → Combustion products + electricity

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH10-2
...
c
ot
og

Aluminium-Air battery

y
...
The cell reaction is:

it

Al3+(aq) + 3OH(aq) → Al(OH)3(s)
Al(s) + 3OH(aq) → Al(OH)3(s) + 3e

O2(g) + 2H2O(l) + 4e → 4OH (aq) (Reduction)
4 Al(s) + 3O2(g) 6H2O(l) → 4Al(OH)3(s)

ve

Net reaction is:

rs

At cathode:

ni

In such a battery the anode is very very pure aluminium and air is bubbled through the
solution at cathode
...

lu

It is expected that this type of battery will find its application in automobiles as source
of energy replacing fuels
...
The common
example of storage cell is lead-acid storage cell
...
The two
types of electrodes are separated by strips of wood or glass fibres
...
The cell reaction is

ch

no

At anode:

ht
tp
:/
/k
er
al
a

te

At cathode:

Pb → Pb2+ + 2e

Pb2+ + SO42 → PbSO4↓
PbO2 + 2H+ + 2e → Pb2+ + 2H2O
Pb2+ SO42 → PbSO4↓

Net reaction: Pb + PbO2 + 4H+ + 2SO42 → 2PbSO4↓ + 2H2O + Energy

It is worthwhile to mention that PbSO4 gets precipitated at both the electrodes
...
The cell loses its function as a voltaic cell
...

Reaction at cathode:
PbSO4 + 2e → Pb + SO42
Reaction at anode:
Net reaction:

PbSO4 + 2H2O 2e → PbO2 + 2H+ + SO42
2PbSO4 + 2H2O + Energy → Pb + PbO2 + 4H+ + 2SO42

After charging the cell restores its original condition and is again used
...

Solar Battery
In this type of battery, solar energy is utilised to generate electric current in a photovoltaic
cell
...
blogspot
...
PM5

sp

251

ELECTROCHEMICAL CELLS

251

...
Due to this contact, a limited number of electrons can flow and cross the junction
between the two types of semiconductors
...

SOLVED EXAMPLES

rs

it

Example 1
...
296 V when [Cu+2] = 0
...

= ∈° +

0
...
0592
log [M + n ]
n

ni

∈ = ∈° +

Sol
...
0592
log 0
...
296 0
...
8239)] V
= [0
...
05398] V
= 0
...

Example 2
...
15 (M) Cu+2 solution
...
34 V (R = 8
...
K1 mol1, T = 298 K)
...

∈ = ∈° +

lu

∈° = ∈

ch

no

lo

gi

ca

∴

RT
ln [M + n ]
nF

= 0
...
303 × 8
...
303 × 8
...
15
2 × 96500
= 0
...

Example 3
...
1 M) and zinc in zinc sulphate (0
...

Sol
...
1 M) || ZnSO4 (0
...
34 +

Zn+2 + 2Ag

FG
H
F
= G ∈°
H

Ecell = ∈°Zn +
Zn

+

Zn + 2Ag+

IJ FG
K H
I F
]J − G ∈°
K H

IJ
K
I
]J
K

RT
RT
ln [Zn +2 ] − ∈° Ag +
ln [ Ag + ]2
2F
2F
RT
ln [ Zn + 2
2F

Ag

+

RT
ln [ Ag +
F

= ( 0
...
0296 log 0
...
798 + 0
...
1)
= 1
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH10-2
...
c
rs

• If we cannot make right choice during construction of a cell, Ecell would come out
negative, but the table of ∈° values and the above procedure will help to calculate
Ecell of any reversible cell
...
Calculate the e
...
f
...
001 M and 0
...
The standard potential of cell is 1
...

Sol
...
0592
0
...
001
= 1
...
0296 log 100
= 1
...
0296 × 2
= 1
...

Example 5
...
m
...
of the cell:
Ni | Ni+2 1(M) || Pb+2 1(M) | Pb
at 25°C
...
Given ∈°Ni = 0
...
13 V at 25°C
...

E°cell = ∈°right ∈° left
= ( 0
...
24)
= 0
...

Cell reaction:
At anode:
Ni 2e
Ni+2 (Ox)
+2 + 2e
At cathode:
Pb
Pb (Red)

ht
tp
:/
/k
er
al
a

te

ch

no

lo

gi

ca

= E°Cell +

Ni + Pb+2
Ni+2 + Pb
Example 6
...
Also find out the standard emf of the cell, given
that ∈° Zn/Zn +2 = 0
...
8 V at 25°C
...
∈° = ∈° Zn / Zn +2 = 0
...
8 V
Ox

i
...
, ∈°Red = ∈Zn +2 / Zn = 0
...
e
...
8 V
...
R
...
So, Ag-electrode will
form right hand half cell i
...
, +ve electrode
...

Cell reaction ⇒
At cathode:
2Ag+ + 2e
At anode:

Zn 2e
2Ag+ + Zn+2

2Ag (Reduction)
Zn+2

(Oxidation)

2Ag + Zn+2

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH10-2
...

bl

Highlights:
• If after calculation of Ecell it comes negative, half cells are to be reversed to get
positive value of Ecell
...

og

253

ELECTROCHEMICAL CELLS

...

bl

= 0
...
76) = 1
...

Example 7
...
1 M and 0
...
Write the scheme of the cell and calculate its
e
...
f
...

Cell = Cu/Cu+2 (0
...
1 M)/Cu

rs

Sol
...
0592
log 2 , here C2 = 0
...
01 M
C1
n

Ecell =

0
...
1 0
...
0296 V
...
01 log 10

ni

ve

Ecell =

lu

Example 8
...
316 J
...
S
...
P
...

gi

= 0
...
E
...
(Ox) for Cu electrode = 0
...
∈° Zn / Zn +2 = 0
...
337 V

ht
tp
:/
/k
er
al
a

∴

te

Cell reaction:

∈°Cu +2 / Cu = 0
...
∈° = 0
...
e
...
765 V

no

and

lo

i
...
,

Zn+2
...
765 V

Zn 2e

Zn + Cu+2
K=

Zn+2 + Cu (E°cell = ∈°Red + ∈°OX) = 1
...

[Zn +2 ] [Cu]
[Zn] [Cu +2 ]

∈Zn +2 / Zn = ∈° Zn +2 / Zn +

0
...
059
[Cu + ]
log
2
[Cu]

At equilibrium, these two electrode potentials will be equal
...
0592
[Zn +2 ]
0
...
337 ( 0
...
0592
[Zn +2 ] 0
...
0592
[Zn +2 ]/[Zn]
log
2
[Cu +2 ]/[Cu]

1
...
0296 log

[Zn +2 ]/[Cu]
[Cu +2 ]/[Zn]

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH10-2
...
c
ot
og
bl

= 0
...
102
= 37
...
0296
K = Antilog 37
...
697 × 1037
...

log10 K =

it

∴

rs

Highlight:

• The high value of K indicates the spontaneity of the reaction
...
Calculate the potential of an Ag-electrode in a solution that is saturated
with AgI and has an iodide concentration of exactly unity
...
3 × 1017,

∈° Ag + / Ag = + 0
...

K sp

lu

Sol
...
3 × 10 −17
= 8
...

I
1
Example 10
...
29 V at 298 K as measured against normal hydrogen electrode
...

Sol
...
0592 pH)
= 0
...
29
≈ 4
...

=
0
...
0592
Example 11
...
The e
...
f
...
123 V
at 25°C
...
2415, ∈Q/H2Q = 0
...

Sol
...
123 = (0
...
0592 pH) 0
...
0592 pH = 0
...
2415 0
...
3345

or
or

pH =

te

ht
tp
:/
/k
er
al
a

∴

0
...
65
...
0592
Example 12
...
2223

Sol
...
798 at 25°C
...

∆G° = nFE°

∈° = 0
...
2223
E°cell = 0
...
blogspot
...
PM5

255

sp

255

ELECTROCHEMICAL CELLS

...
2754 = 1
...

og

rs

SHORT QUESTIONS AND ANSWERS

bl

nFE°
1 × 0
...
7246 = 10 + 0
...
303 RT
0
...

or

log K =

it

or

ENGINEERING CHEMISTRY

Q
...
What is galvanic cell or voltaic cell?

ni

ve

Ans
...
g
...
Such a cell is also known as electrochemical cell
...
10
...

Q
...
What is an electrolytic cell?
Ans
...

Q
...
What do you mean by electrode potential (E)?
Ans
...

Q
...
What are reduction and oxidation potentials?
Ans
...

Q
...
What do you mean by standard electrode potential (E°)?
Ans
...

Q
...
What is a salt bridge?
Ans
...
g
...
It connects
(acts as a bridge) the solutions of the two half cells
...
7
...
M
...
of a cell?
Ans
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH10-2
...
c
ot
og

sp

257

ELECTROCHEMICAL CELLS

ni

ve

rs

it

y
...
8
...

Ans
...
Its electrode potential is taken as
zero at all temperatures
...
It can be represented as:
Pt, H2 (1 atm) || H+ (1 M)
1
Reaction:
H+(aq) + e → H 2 ( g)
2
1
H 2 ( g) → H+(aq) + e
or
2
Q
...
How is electrode potential measured?

ca

lu

Ans
...
10
...

Saline bridge

Inert
electrode (Pt)

no

+

lo

gi

H2
(1 atm)

H (a=1)

Pt

Redox system
B

ch

A

Fig
...
17 A cell constructed with standard hydrogen electrode
...

Saline bridge has the function of bringing into physical contact the two solutions without
mixing them; it consists of a strong electrolyte (e
...
, KCl)
...
10
...
M
...
of a cell measured?
Ans
...
M
...
of a cell is measured by means of a device, named potentiometer
...
10
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH10-2
...
c
ot
og

ENGINEERING CHEMISTRY

Q
...
What do you mean by potentiometry?

ve

rs

it

y
...
Potentiometry is an electrochemical method of analysis based on measuring the
potential difference (e
...
f
...

Q
...
What is an indicating electrode?
Ans
...

Q
...
Give the hemistry the different indicating electrodes
...
(a) First Class ⇒ Metallic electrodes in contact with a solution of their own ion
(an electrode which is reversible in relation to the cation)
M; where, [Mn+] ⇒ conc
...
059
log [M n ]
n
(b) Second class ⇒ Metallic electrodes in contact with one of their not readily soluble
salts and with the anion of this salt:
M | MA(s), An
where,
M ⇒ Metal
MA(s) ⇒ the salt which is not readily soluble
...
of the anion in moles dm3
...
059
0
...

ch

no

lo

gi

ca

lu

∈ = ∈° M / M n+ +

te

(c) Redox = Electrodes which are inert in contact with a redox couple in solution
...
059
log [Ox]/[Red]
n
Pt ⇒ Platinum
[Ox] = Conc
...

[Red] = Conc
...

(d) Membrane type = Selective electrodes specific to certain ions
...
The best known of
this type is glass electrode
...
059
log a
n
where, ∈r ⇒ Constant potential linked to the choice of the reference electrode and the internal
solution, a ⇒ activity of the ion in relation to which the electrode is selective
...
14
...
These are the electrodes whose potential is constant and independent of the
composition of the contacting solution
...
246 V) and the silver-silver
chloride electrode (∈ = + 0
...

∈ = ∈r +

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH10-2
...
c
ot
og
bl

Highlight:

y
...

Q
...
Define the electrochemical series?

rs

it

Ans
...

Q
...
What is Nernst equation?

ve

Ans
...
303 RT
[Reduced form]
log
nF
[Oxidised form]

ni

∈Red = ∈°Red
R ⇒ molar gas constant
...

n ⇒ number of electrons involved in the redox reaction
...

lo

∈Red = observed reduction electrode potential
...
303 RT/F comes out as equal to 0
...

ch

So at 25°C

te

∈ = ∈°

0
...

Q
...
What is lead storage battery?
Ans
...

Reactions:
Anode:
Cathode:

PbO2 +

SO42

Pb + SO42 → PbSO4 + 2e
+ 4H+ + 2e → PbSO4 + 2H2O

Net reaction: Pb + PbO2 + 4H+ + 2SO42 → 2PbSO4 + 2H2O
...
18
...
Anode:
Cd(s) + 2OH(aq) → Cd(OH)2(s) + 2e
Cathode:
NiO2 + 2H2O + 2e → Ni(OH)2 + 2OH (aq)

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH10-2
...
c
ot
og

ENGINEERING CHEMISTRY

Q
...
What are fuel cells?

Q
...
Give the reaction in H2O2 fuel cell
...

bl

Ans
...

Ans
...

ca

Q
...
What do you mean by corrosion?

gi

Ans
...
g
...

Q
...
Classify corrosion
...
(a) Chemical corrosion ⇒ it involves direct chemical action between metals and

lo

gases
...

(c) Dry corrosion ⇒ it refers to the corrosion of metals involving direct chemical action
between metals and dry gases
...

Q
...
State the electrochemical theory of rusting
...
Reaction:
Anode:
Cathode:

OH

Fe → Fe2+ + 2e
2H2O + O2 + 4e → 4OH
...
e
...

2Fe+2 + H2O + O → 2Fe+3 + OH
2Fe+3 + 6OH → 2Fe(OH)3 or Fe2O3
...
24
...
(a) Barrier protection
...

(c) Electrical protection
...

Q
...
Given (i) Fe+2 + 2e → Fe,
∈° = 0
...
77 V
(ii) Fe
→ Fe
Represent the data in the form of Latimer diagram
...
blogspot
...
PM5

260

sp

260

...
We have

∆G°(i) = nFE° = 2F ( 0
...
88 F

Adding the above two equations,
∆G°(iii) = ∆G°(i) + ∆G°(ii) = 0
...
77) F = + 0
...

bl

∆G°(ii) = nFE° = F(0
...
77 F

rs

Fe+3 + 3e → Fe

∆ G° + 0
...
04 V
−n F
−3F

ve

∈° =

0
...
44

+2

Fe

ca

–0
...
10
...

Fe

gi

Fig
...
19 Latimer diagram for Fe species
...

no

Q
...
In alkaline solution (pH = 14) the Latimer diagram for chlorine is
+ 0
...
30

–

+ 0
...
42

+ 1
...
ClO →

ClO → Cl
...
42 V;

∆G°I = (+ 0
...
42 F

1
+e
Cl → Cl,
∈° = + 1
...
78 F

∆G°II = (+ 1
...
36 F

From the relation, ∆G° = nFE°
∈° (ClO/Cl) =

∆ G I + ∆ G II − 178 F

...
89 V
=
− nF
−2F

Q
...
Use the following data to draw a Frost diagram
...
18 V,

∈°(Mn+3,
∈

Ans
...
36 V
∈

= 1
...

Mn) = 1
...
95 V
3∈°(Mn+3, Mn) = 0
...
10 V

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH10-2
...
c
ot
Mn

6+

y
...
10
...

ht
tp
:/
/k
er
al
a

te

Highlights:
• Plot of n∈° vs n for Mn (n = oxidation state) such diagram are called Ebsworth diagram
or Frost diagram
...

• A state is unstable with respect to disproportionation if it lies above the line connecting
two adjacent oxidation states
...
Since both these products involve
one electron transfer, the process is likely to be rapid
...

• MnO2 is also a strong oxidizing agentits slope to Mn+2 is greater than the slopes to
higher oxidation states
...

• The minimum at Mn+2 suggests this to be the common product of reduction of MnO4
[Mn(VII)] in acidic solution and it is the most stable oxidation state of Mn
...
28
...

+3

Tl

+1
...
34

Tl

+1
...
The oxidation states of Tl are + 3, + 1 and 0, in the three species
...
e
...
34 V, here n = 1, so, n∈° = 0
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH10-2
...
c
ot
og

For the change of oxidation number from + 3 to 0

it

y
...
23 V
So, for n = 3, n∈° = 3 × 1
...
69 V
...
10
...

ch

no

Tl+1 is the most stable oxidation state of Tl as the species lies lowest in the Frost diagram
...

Define the electrode potential
...

What is a standard hydrogen electrode? What is its potential?
What is overvoltage? What is the cause of overvoltage?
Give the reason: the hydrogen overpotential falls with rising temperature
...

Why is a voltmeter is not used for the measurement of e
...
f
...

What is a calomel electrode? Describe its construction: Why it is used as reference electrode in
place of a standard hydrogen electrode?
What is an electrochemical series?
Why are standard potentials of Zn/Zn +2 and Cu/Cu+2 electrodes opposite in sign?
Describe the construction and working of H2 O2 fuel cell
...

Describe the construction of a glass electrode
...

What are primary and secondary reference electrodes?
Write a note on decomposition potential
...

ht
tp
:/
/k
er
al
a

1
...

3
...

5
...

7
...

9
...

11
...

13
...

15
...

17
...

19
...
blogspot
...
PM5

263

sp

263

ELECTROCHEMICAL CELLS

...
Distinguish: (i) a reversible cell from an irreversible cell

bl

(ii) a galvanic cell from a concentration cell
...

21
...

22
...
What is fuel cell? Give detail of one such cells
...
What are reversible and irreversible cells?

rs

25
...

26
...

28
...

ni

27
...

lu

29
...

30
...
Write down the electrode reactions and overall cell reactions for the following cells
...
m
...

gi

(i) Zn | ZnSO4 || CuSO4/Cu

(ii) (Pt) H 2 (1 atm) | HCl/AgCl(s), Ag

lo

32
...

no

(ii) Calculation of solubility product of AgCl
...
The reaction H2 + Cl2 + 2H2O
2H2O + 2Cl has an equilibrium constant K = 1046 at 25°C
...

ht
tp
:/
/k
er
al
a

te

34
...
337 and 0
...
Give
the equilibrium constant for the reaction,
2Cu+

Cu2+ + Cu

35
...
01 (M) ZnSO4 solution at 25°C
...
763 V (0
...
Calculate the e
...
f
...
Given the electrode potentials of
Cu and Fe are 0
...
44 V, respectively
...
78 V)
...
Will a reaction take place if an Ag-bar is placed in a solution of FeSO4? Explain using the following data:

∈°Ag + / Ag = 0
...
44 V ( 1
...
Calculate the e
...
f
...
001 M and 0
...
The standard potential of the cell is 1
...
13 V)
...
Calculate the e
...
f of the following concentration cell:
Ag/Ag+ (0
...
0
...
The e
...
f
...
0 N)| Quinhydrone | Pt
is 0
...
Calculate the pH of the solution
...
2812 V and E° for the quinhydrone electrode is 0
...

[Ans
...
5]

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH10-2
...
c
ot
og

41
...
001 N) in 0
...
01) | Hg+

bl

it

Fe+2 +

[Ans
...
2]

y
...
Find the equilibrium constant of the reaction at 25°C
...
2
...
Calculate the equilibrium constant of the reaction at 25°C
...
44 V, ∈°Fe +3 / Fe ⇒ 0
...
5355 V
...
K = 166]

ht
tp
:/
/k
er
al
a

te

ch

no

lo

gi

ca

lu

44
...

[Ans
...
When calomel electrode is connected to H2-electrode at 18°C, gives e
...
f
...
5622 V
...

[Ans
...
4]
46
...
m
...
of the cell, which is constructed by connnecting H2-electrode to normal calomel electrode,
at 25°C in 0
...
Calculate its (i) pH and (ii) H+ concentration
...
(i) 6
...
16 × 107]

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH10-2
...
c
ot
sp
og
bl

it

y
...
We all know that a homogeneous system is one in which both the reactants and products
are of one phase (i
...
, solid, liquid or gas) and a heterogeneous system is one in which they are
in different phases
...

no

lo

1
...
Phase is defined as any physically distinct portion of matter which itself is
homogeneous and uniform in composition, mechanically separable from other parts by definite
boundary surfaces
...

Thus mixture of H2 and O2 constitutes single phase
...

(c) Solution of a solute in a solvent constitutes single phase such as salt solution in water
...

(e) Except solid solutions all different kinds of solids form different phases
...

( g) At freezing point, water consists of three phases:
Ice(s)

Water(l)

Water vapor( g)

(h) A heterogeneous mixture of the type
CaCO3(s)

CaO(s) + CO2( g)

consists of three phasestwo solid and one gaseous
...
Component
...

This concept of component can be explained in connection with phase rule with the help
of the following examples
...
e
...
So, it is a one-component system
...

266

http://keralatechnologicaluniversity
...
com

...

bl

(c) In the thermal decomposition of MgCO3,
MgCO3(s)
MgO(s) + CO2(g)
...

(d) Suppose a solid dissociates into a number of gaseous substances in a closed vessel
NH4Cl(s)
NH4Cl(g)
NH3(g) + HCl(g)
The overall composition of the dissociated vapour (NH3, HCl) is exactly the same as that
of the undissociated substance (NH4Cl)
...
However, if
NH3 or HCl is introduced in the system in excess, the system becomes a two-component system
...
The composition of each phase can be expressed
in terms of Na2SO4 and H2O, so the system is a two-component system
...

3
...
The number of degrees of freedom of a system is
the minimum number of the independent variables of a system, such as temperature, pressure
and concentration, which can completely define the equilibrium of a system
...
It is a one component, one-phase
system
...
Hence
the degree of freedom is two
...
So this system will have no degree of freedom i
...
, it is a nonvariant or invariant system
...

(c) For the system, NaCl(s)
NaCl-Water(aq)
H2O(g) the solubility at the
saturation point is fixed by either temperature or pressure, so the system is univariant
...

The Phase Rule

The rule can be stated as the sum of the number of phases and the degrees of freedom
of any system exceeds the number of components by two, provided that the only significant
external factors acting are temperature, pressure and concentration and not influenced by
gravity, surface action, magnetic or electric forces
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH11-1
...
c
ot
og

ENGINEERING CHEMISTRY

Examples 1
...

bl

Vapor ( g)

Water(l)

Hence F = 1 2 + 2 = 1
...

(a)

(b) For water at critical point
C = 1, P = 3
...

CaO (s) + CO2 ( g)

C = 2, P = 3
...

ni

Advantages of phase rule

ve

(c) For CaCO3 (s)

Vapor ( g)

it

Water (l)

rs

Ice (s)

lu

1
...

2
...

ca

3
...

gi

4
...

no

lo

5
...

ht
tp
:/
/k
er
al
a

te

ch

Limitations of phase rule
1
...

2
...

3
...

Phase diagram
The conditions of equilibrium between different phases of a substance can be shown by
plotting temperature and pressure as variables and the diagram is called the phase diagram
...

The Water System
This system consists of three phasesice, water, vapor and one-component H2O
...
11
...
The point B has a natural limit of 273°C,
beyond which the two phases merge
...
The OA
curve terminates at A, the critical temperature of +374°C above which distinction between
liquid and vapor vanishes
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH11-1
...
c
ot
og
bl

C
218 atm

y
...
0075 °C

100 °C

374 °C

ca

Temperature

ni

Z

Ice

B

ve

1 atm

lu

Pressure

Water

4
...
11
...

lo

Since F = 1 there is only one degree of freedom i
...
, if the temperature is fixed, all other
properties are also fixed
...
e
...
e
...
0098°C under 4
...
e
...
The curve OC represents the change of melting point of ice with pressure
...

The curves OA, OB and OC divides the whole region into three portions AOC, BOC and
AOB in which only one phase is present and so the system becomes bivariant and to locate any
point in these areas, temperature as well as pressure is to be known because the degree of
freedom F = 1 1 + 2 = 2
...
This curve represents a metastable system
...
e
...

Sulfur System
...
Sulfur at low temperature is in the rhombic form and at high temperature in the
monoclinic form
...

In the phase diagram for sulfur (Fig
...
2), AB is the vapor pressure curve of rhombic
sulfur which is stable upto 95°C (0
...
BC is the similar curve of monoclinic sulfur
and the point B is the transition point between the two allotropes of sulfur
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH11-1
...
c
ot
og

ENGINEERING CHEMISTRY

F

bl

SR

y
...
03 mm)

rs

D

ve

C(120 °C, 0
...
6 °C, 0
...
11
...

lo

gi

ca

Hence, B is actually the triple point
...
04 mm) monoclinic sulfur
melts and CD is the vapor pressure curve of liquid sulfur
...
These two
lines meet at E (151°C, 1288 atm) which is again a triple point where rhombic, monoclinic and
liquid sulfur co-exist in equilibrium
...

F=CP+2

ht
tp
:/
/k
er
al
a

Phase (P): Phase is defined as any physically distinct portion of matter which is
itself homogeneous and uniform in composition, mechanically separable from other
parts by definite boundary surfaces
...

Degrees of freedom (F): It is the minimum number of independent variables of a
system, which can completely define the equilibrium of a system, such as
temperature, pressure, concentration
...
Curve BG is the metastable vapor pressure curve of rhombic sulfur
...
There are three stable and one unstable triple points and
four phases co-exist nowhere in the curve in equilibrium
...
e
...

Along the lines AB, BC, CD, BE, CE and EF two phases co-exist and F = C P + 2 =
1 2 + 2 = 1, i
...
, the system is univariant and either temperature or specific volume determines
the system completely
...
blogspot
...
PM5

270

sp

270

...

Thus actual observation can be explained perfectly in terms of phase rule
...

it

Phase Rule for Two-Component Alloy Systems

ve

rs

For a two component system, the highest degree of freedom F = C P + 2 = 2 1 + 2 = 3
i
...
, the behaviour of a system may be represented by a three-dimensional diagram of pressure,
temperature and composition which cannot be drawn on a paper
...
Thus now the system is present at atmospheric pressure and it remains constant,
which will reduce the degrees of freedom by one i
...
, F = C P + 1 and the system is called
condensed system
...

gi

Eutectic Systems

no

lo

The cooling curve of a pure substance can be represented as Fig
...
3 (a)
...

a

a

Freezing
point
Temperature

Temperature

ht
tp
:/
/k
er
al
a

te

ch

The cooling curve of a mixture of solid is represented by Fig
...
3 (b)
...
The temperature decreases continuously but at different
rate than before freezing point
...
The system becomes invariant, temperature remains constant until
total solidification occurs (along cd) and again temperature falls uniformly along de
...
11
...

From the cooling curve of any mixture of definite composition freezing point and eutectic
temperature both can be obtained
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH11-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

272

bl

If the composition of the mixture coincides with the eutectic composition, there is no
double break but the curve mimicks that of pure component
...

By plotting freezing point against composition, T-C curve is obtained for alloy system
...

O

2
...
4 Pb

Solid Pb
+
Liquid
Eutectic
+
Solid Pb
100% Pb

lo

Composition

no

Fig
...
4 T-C diagram of Pb-Ag system
...

ch

A binary system consisting of two substances which do not react chemically but is miscible
in all proportions in liquid phase is called eutectic system
...

The eutectics are applied for constructing safety devices in boilers, automobiles etc
...
At constant atmospheric pressure, the vapour phase is absent and the
condensed phase rule is applicable as F = C P + 1
...
A is the melting point (961°C) of
Ag
...
This point O is the eutectic point (2
...
4 % Pb) and the whole
mass at this point crystallizes out with the above fixed composition
...
According to reduced phase rule equation, the system
is univariant along AO and BO and at point O, F = 3 P = 3 3 = 0 i
...
, invariant, which is the
eutectic temperature and a lead-silver mixture can never have a melting point below the eutectic
temperature
...
blogspot
...
PM5

272

...

bl

The region above the curve AO and BO represents solution of Pb and Ag and below the
curve AO represents solid eutectic with crystalline Ag and below the curve BO represents solid
eutectic with crystalline Pb
...
11
...
When
Mg is added to Sn, the melting point of Sn (232°C) lowers along PQ
...
So Q is the invariant
eutectic point
...
Thus along QR from molten alloy only solid compound crystallizes out in
equilibrium with the liquid
...

This temperature (783°C) is the congruent melting point of the compound, which is Mg2Sn
...
11
...

Further increasing the magnesium, the freezing point decreases along RS and reaches
the second eutectic point S (565°C)
...
At the eutectic points the solid compound is in equilibrium with either solid tin or solid
Mg
...
The compound formed is
stable and has its melting point at the maximum
...

Iron-Carbon Alloy System
The equilibrium diagram of Fe-C is especially useful to understand the heat treatment
of steel
...
67% weight of carbon
...
C atoms being small compared to
iron atoms form only interstitial solid solutions and the solubility of C in these allotropes is
quite different
...
blogspot
...
PM5

273

...
025%
Ferrite
Pearlite
+
Ferrite

M

6

6
...
0
4 4
...
4 0
...
8 1
...
0
Hypoeutectoid
Hypereutectoid
Cast iron
Steels
x
Weight %C

no

Wrought
iron

Pearlite
+
Cementite

Cementite
+
Pearlite
+Transformed
Ledeburite

gi

0
...

A

1600
1539
1500

og

ENGINEERING CHEMISTRY

Fig
...
6 Equilibrium diagram for Fe-C system
...
Above the liquidus there is only liquid phase whereas below the solidus there is only solid
phase and between the two lines both phases are present
...
3% C by weight
...
67% C content and it is called cementite
...
The phase diagram
indicates that upto 0
...
088% to 2% C content is
steel and C content above 2% represents cast iron
...
Area DCH represents cementite
and liquid
...
e
...

The transformation of one solid phase into another takes place at the critical temperatures
indicated on the diagram
...
On further
cooling, austenite separates out from the liquid, then at 1130°C, the mixture is austenite
containing 2% C and liquid has eutectic composition
...
Cooling
further leads to the decomposition of the eutectic mixture of cementite and finally at 723°C the
residual austenite transforms to pearlite and at temperature below 723°C, all the ledeburite is
transformed into pearlite and cementite mixture
...
e
...
But with faster cooling rates metastable phases like
martensite and bainite are formed which are not shown in the phase diagram
...
blogspot
...
PM5

274

sp

274

...

Condensed phase rule
...
So the
system is considered to be under atmospheric pressure which reduces the degrees
of freedom by one and hence,

rs

F=CP+1

lu

ni

ve

Triple point
...
At triple point the system is nonvariant
...
A solid solution of two or more substances having lowest freezing
point is the eutectic mixture and the minimum freezing point attained is the eutectic
point
...
A compound possesses congruent melting point if it
melts to give a liquid having the composition same as the solid
...
An alloy of Cd and Bi contains 25% Cd
...

Sol
...

ch

In 1 kg alloy content of Cd is 25%, i
...
, 250 gm
...

40

∴ The mass of eutectic in 1 kg alloy is (250 + 375) gm = 625 gm
...

ht
tp
:/
/k
er
al
a

sp

275

PHASE RULE

Problem 2
...
AB on cooling forms eutectic containing
60% A and 40% B and the rest of B
...
In 1 kg of AB, A = 40 % = 400 gm and B = 60% = 600 gm
...

∴ Corresponding to 400 gm A, the content of B =

400 × 40
= 266
...
7) gm = 333
...
Ans
...
1
...

Ans
...

Q
...
What is condensed phase rule?
Ans
...

Q
...
Define the following terms:
(a) Phase (b) Component (c) Degrees of freedom
...
blogspot
...
PM5

275

...
(a) See page 266
...

bl

(b) See page 266
...

it

Q
...
What is triple point?
Ans
...

rs

Q
...
What is an invariant system? Give an example
...
A system in which the degree of freedom is zero is called an invariant system
...

ni

ve

Example: Triple point of water is where ice, water and water vapour are in equilibrium
...
6
...
A triple point for a system is invariant
...
If temperature or volume is altered, one phase of the
substance disappears and the system becomes univariant from invariant
...
7
...

gi

Ans
...

(ii) Phase rule helps to predict the behaviour of a system under different sets of conditions
...
8
...

Ans
...

ch

no

(ii) Phase rule conditions that all phases of the system must be present simultaneously
under similar set of conditions
...
9
...

ht
tp
:/
/k
er
al
a

te

Ans
...

Eutectic composition of Pb-Ag system → 97
...
By suitable choice, very low
melting alloys can be selected for preparing safety devices like fire sprinklers, plugs in
automobiles etc
...
10
...

Ans
...
So there are three phases in equilibrium
...

Q
...
How many degrees of freedom are there for the following systems?
Water vapour(g)
(i) Water(l)

(ii) Gaseous mixture of H2 and O2
Ans
...
Hence degree of freedom is one
...

Q
...
For a two-component alloy system of Pb and Ag, state the degrees of
freedom (i) as per phase rule and (ii) as per condensed phase rule
...
blogspot
...
PM5

sp

276

276

...

bl

Ans
...

(ii) As per condensed phase rule:
For solid-liquid equilibrium of alloy, practically no gas is present and hence at atmospheric
condition the pressure remaining constant, degrees of freedom reduces by one and F becomes
F = C P + 1 = 2 1 + 1 = 2
...

Define the following terms:
phase, component, degrees of freedom
...
What is condensed phase rule?
4
...
Write a brief note on: eutectic point, metastable state
...
Write down the limitations of phase rule
...
What is phase diagram? Explain (a) triple point and (b) eutectic point with reference to phase
diagram
...
Draw and explain the phase diagram of ice-water-water vapor system and show the variation of
melting-point of ice with pressures
...
What are the merits and the limitation of phase rule?
10
...

11
...
Draw and explain the phase diagram of a binary alloy system with simple eutectic formation
...

2
...

2
...

3
...

4
...
6% Pb, 97
...
6% Ag, 97
...

5
...

6
...
In the water system at triple point, the system is
(a) univariant
(b) trivariant
(c) invariant
...
Condensed phase rule has two variables, namely
(a) temperature and concentration
...
Eutectic mixture has:
(a) highest melting point
...

10
...

ht
tp
:/
/k
er
al
a

1
...
blogspot
...
PM5

277

...

bl

12

rs

it

Colloids

ve

INTRODUCTION

ni

Thomas Graham (1861) while doing his classical researches on liquid diffusion observed
two classes of substances
...

To this class belonged almost all inorganic acids, bases and salts and many organic compounds
like urea, sugar etc
...

The other class of substances are diffused very slowly in solution and the solution could
not pass through the membrane, they were called colloids (from the Greek word Kolla meaning
glue, which is a member of this class)
...

te

ch

no

lo

Grahams view has undergone changes since it has been seen that every substance can
exhibit colloidal properties under suitable conditions
...
In a colloidal solution there exists a discontinuous phase called the dispersed phase
and the continuous dispersion medium, and also a stabilizing agent which does not allow the
dispersed phase to coalesce and settle
...
1) of colloids are formed
...
1 Types of colloidal systems
Dispersed
phase

Colloidal
system

Examples

Gas

Liquid
Solid

Liquid aerosol
Solid aerosol

Mist, Fog, Cloud, Insecticide spray,
Smoke, Fume

Liquid

Gas

Foam

Liquid
Solid

Emulsion
Sol

Foam, Froth, Whipped cream,
Lemonade
Milk, Cream, Mayonnaise,
Glue, Paints, Starch paste, Milk
of Magnesia, Gold sol, As2O3, S,
FeO3 or AgCl sol in water

Gas

Solid foam

Liquid

Gel

Solid

Solid sol

Solid

278

Pumice stone, bread dough, Lava,
Styrene foam, Rubber
...

Gems, Alloys, Minerals

http://keralatechnologicaluniversity
...
com

...
2 Characteristics of lyophilic and lyophobic sols

y
...
The main differences between these two classes of colloids are summarised
in Table 12
...

(i) Stable

(ii) The particles are charged and hence
move towards electrode in an electrical
field
...

(iii) Viscosity is same as that of the medium
...

(iv) They are reversible sols
...

(v) They are much less stable, stabilizer is
reqd
...

ca

(v) They are self-stabilized due to the strong
attraction between two phases
...

(vii) They are not easily precipitated by the addition of electrolytes
...

(viii) Starch gelatin, gum, albumin are lyophilic
colloids
...

no

lo

gi

(vi) Surface tension is much lower than that of
the medium
...

(ix) Visible under ultramicroscope
...

te

(x) Prepared simply by direct dissolving
...
They are lyophobic in nature
...

(ii) Macromolecular colloids: A large number of small molecules combine to form a
giant molecule held by covalent bonds having a colloidal dimension are called
macromolecular colloids
...

Examples: Proteins, Polysaccharides, Gums, Synthetic rubber, Nylon etc
...
Example: Soaps and synthetic detergents
...
They move freely in an electric field and the solution has high conductivity
...
These colloids play very important role in solubilizing solvent repellant
substances, such as water insoluble dyes are solubilized in soap solutions
...
blogspot
...
PM5

279

sp

279

COLLOIDS

...

bl

The main methods of preparation of colloidal solutions are (a) Condensation method
(b) Dispersion method
...
The
various processes used are:

rs

(i) By exchange of solvent: Sulfur or phosphorus is not directly soluble in water
...

ni

ve

(ii) By changing physical state: Hg or S sols are produced by allowing their vapours to
pass through cold water
...

lu

(iii) By controlled condensation: Prussian blue sol is obtained by precipitating it in
presence of a protective colloidal system like starch
...

gi

As2O3 + 3H2S → As2S3 + 3H2O
...

no

lo

(b) By reduction: Colloidal solutions of metals such as Ag, Au, Pt in water can
be prepared by reducing aqueous solution of their salts by reductants like formaldehyde, carbon monoxide, hydrazine etc
...
3 %)
...

ht
tp
:/
/k
er
al
a

(c) By hydrolysis: Colloidal solutions of many oxides and hydroxides of iron, aluminium
can be prepared by this method
...

FeCl3 + 3H2O → Fe(OH)3 (sol) + 3HCl

(d) By oxidation: Sulfur sol is prepared by passing H2S through a solution of SO2 in
water until the smell of SO2 is removed
...

(B) Dispersion method: In this method, the bigger or large particles are broken down
to colloidal dimension and dispersing them in a medium to form colloidal solution
...

The space in between the metal discs breaks down the particles to colloidal size
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH12-1
...
c
ot
og

sp

281

COLLOIDS

it

y
...
1) Colloidal solution of metals
like Au, Ag, Cu, Pb, Pt etc
...
An electric current is passed through
water containing traces of alkali, when an electric arc is produced between the tips of two
closely placed electrodes of these metals
...
The trace of
alkali stabilizes the colloidal solution and finally the solution is cooled by cooling mixture
...
12
...

ht
tp
:/
/k
er
al
a

te

ch

(iii) Mechanical dispersion method: (Fig
...
2) this technique consists of finely pulverising
the substances to be dispersed in the medium, which constitutes the dispersion phase
...
The colloid-mill consists of two discs made of metal, which rotates in opposite direction
at a very high speed
...
The coarse particles which come in between the two rotating
discs get teared to smaller colloidal particles, which are finally stabilized by addition of a
suitable protective colloid
...
12
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH12-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

282

bl

(iv) Peptization: A freshly prepared precipitate such as AgCl, Fe(OH)3, Al(OH)3 etc
...

The foreign electrolyte is known as the peptizing agent and the process is called peptization
...
Fe3+

→

Peptizing agent

(Colloid/Sol)

rs

Precipitate

it

y
...

(b) Freshly precipitated AgCl can be peptized by shaking with a dilute aq sol
...
H+

lu

(c)

Peptizing agent

ni

Precipitate

AgCl
...

lo

Purification of Colloidal Solutions

gi

Dispersion is also sometimes carried out by the use of an atomiser e
...
, in the dispersion
of a liquid in a gas
...
So, they become unstable
...
The following methods are commonly used for purification
...
The semipermeable membranes like cellophane parchment paper, animal
membrane have pore sizes which allow the free passage of only the dissolved molecules or ions
of a true solution but retains the bigger colloidal particles
...

The sol to be purified is taken in a parchment or cellophane bag, which is partly immersed
in water or the dispersion medium
...
The solvent is renewed
from time to time
...
In certain sols such as Al2O3 hydrosol, the
disperse phase is too small to be retained by cellophane and hence the system needs controlled
heating whereby the particles grow bigger in size
...
12
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH12-1
...
c
ot
og

sp

283

COLLOIDS

D

E

H2O

+
H2O

n

ni

Sol
A

ve

–

rs

it

y
...
Electrodialysis is of no use in separating non-electrolytic impurities
...
12
...

no

lo

gi

ca

(ii) Ultra-filtration
...
But
when ordinary filter paper is impregnated with a solution of gelatin or collodion and hardened
by formaldehyde the pores become smaller, so that colloidal particles cannot pass through it
...
The sol when poured over the ultrafilter, electrolytes can pass through, but the colloidal particles are retained and form a slime over it
...
This
process of purifying colloids from the crystalloids using ultrafilters is called ultrafiltration
...

Colloidal solutions possess some characteristic properties
...

(b) Colour
...
Gold sol of very fine particles is red
and of coarser particles is blue in colour; sulfur sols may be colorless to faint and
deep yellow in reflected light and reddish in transmitted light
...
Although the most common shape of the particles are spherical; but highly
asymmetrical shape is also found
...
Colloidal particles are readily filterable through ordinary filter paper
...
Generally colloidal particles are either positively or negatively
charged, so they attach to a variety of molecules on their surfaces
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH12-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

284

y
...
High molecular weight is the characteristic of colloidal
particles and hence in a solution, the number of moles present is very low
...

it

(iii) Mechanical properties

lu

ni

ve

rs

(a) Brownian movement
...
This random zigzag motion is also executed by all colloidal particles, including colloidal particles suspended in a gaseous medium, independent
of their nature, smaller particles executing a more rapid and brisk motion than
the larger ones
...
This
motion is described by Perrin as they go and come, stop, start again, mount,
descent, remount again, without in the least tending towards immobility
...
The colloidal particles are constantly hit from all sides of the surrounding molecules
...
The intensity of Brownian motion is less with increase in size of the colloidal particles and also with the increase in viscosity of medium
...
Large particles
do not show Brownian movement
...
In a colloidal solution, colloidal particles move from a region of higher
concentration to a region of lower concentration until uniformity is attained
...
Diffusion is used to separate colloidal particles of different size
...
Colloidal particles constantly exhibit Brownian motion and remain
suspended in solution, thereby stabilizing the colloidal solution
...
Svedberg
increased the rate of sedimentation with centrifugal sedimentation by employing
a high-speed centifuge called ultracentrifuge
...

(iv) Optical properties or Tyndall effect
...
This phenomenon is called Tyndall effect, which does not happen for true
solution
...
The phenomenon of Tyndall effect can be
explained by the scattering of light by the colloidal particles
...
The intensity of the scattered
light depends on the difference between the refractive indices of particle and medium
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH12-1
...
c
ot
bl

og

sp

285

COLLOIDS

–

+

Powerful
beam of light

rs

Path is
invisible
Colloidal
solution

True solution

Electrophoresis

ve

Path is
visible

it

y
...
12
...

Fig
...
6 Electrophoresis
...
Lyophilic and lyophobic colloid particles are either positively or
negatively charged
...
After reaching the electrode, they lose their charge and coagulate there
...

When the negatively charged particles like CdS, As2S3 metallic sols, organic sols
move towards cathode, the phenomenon is called cataphoresis
...
The speed of the colloidal particle
under the potential gradient of 1 volt/cm is called electrophoretic mobility
...
When electric current is passed
through a colloidal solution such that the dispersed
+
–
phase is prevented from movement, the dispersion
medium begins to move in the electric field
...
12
...

ht
tp
:/
/k
er
al
a

(c) Isoelectric Point
...

Fig
...
7
Hence the pH of the dispersion medium at which
the dispersed particles are neutral and hence they do not migrate when subjected
to an electric field is called isoelectric point
...
Proteins are least soluble in
isoelectric point and hence coagulate at isoelectric point
...

When the charge is neutralised, the particles approach each other to form aggregates and
settle down
...
This
can be achieved by
(i) Adding oppositely charged: Two oppositely charged colloidal solutions when mixed,
mutual coagulation of the two sols takes place
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH12-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

286

it

Na+ < Ba+2 < Al3+ or Cl < SO 2− < PO 3−
...

bl

(iii) Adding electrolytes: By addition of oppositely charged ion i
...
, by adding electrolytes
the charges of the colloidal particles are neutralised and precipitated
...
The higher the valency of the
ion, greater is the coagulating powerthis is known as Schulze-Hardy law
...

ve

Protection of Colloid

The stability of colloids can be achieved by any of the following:

lu

ni

(i) Electrical charge
...
This mutual repulsion prevents them from coalescing and coagulating
...
Colloidal particles are surrounded by a layer of solvent molecules which
resists the dispersed phases from forming large aggregates and coagulate
...
These sols are very stable
...
Protective agents are added to some colloidal systems, which
get adsorbed on the surface of the colloidal particles and by coating them prevents coagulation
...
Lyophilic colloids are much more stable than the lyophobic
colloidssince the former are extensively solvated
...
The process
by which lyophilic colloid protects the lyophobic sol is called protection and the lyophilic colloid
is called the protective colloid
...
This protection is due
to the formation of a protective thin layer surrounding the particles of the lyophobic colloid,
through which the oppositely charged ion of the electrolyte cannot penetrate to neutralize the
charge for coagulation
...
It is defined as the minimum weight in mg of a protective
colloid, which when added to one ml of standard gold sol (containing 0
...
0058 % gold)
containing also 1 ml of 10 % NaCl solution to just prevent its coagulation
...
The smaller the gold number the greater is the protective power of lyophilic colloid
...
3 Gold numbers

Protective colloid

Gold number

Gelatin

0
...
015

Casein

0
...
02

Albumin

0
...
2

Gum

0
...
2

Starch

10 to 15

Sodium oleate

0
...
003 to 0
...
blogspot
...
PM5

286

...

bl

Emulsions are colloidal systems in which both dispersed phase and dispersion medium
are liquids (immiscible)
...

Emulsions are prepared merely by shaking one liquid with the other, and hence they
are not stable and easily separate into two immiscible layers
...
This substance forms a thin layer around
the dispersed phase thereby preventing it from coalescing and coagulating
...

Albumin, casein, gum, agar-agar, soaps and detergents are the common emulsifiers
...
g
...
are more soluble in aqueous phase, hence they are used as stabilizers for oil-in-water-type
of emulsion whereas heavy metal soaps of palmitic and oleic acid are soluble in fat and hence
used in water-in-oil-type emulsion
...

Gel: Many lyophilic sol and few lyophobic sol when coagulated under certain conditions
form semi-solid mass
...
g
...
This is formed by entrapment of the dispersion medium inside the loose
network of the dispersed particle
...

Gel formation is utilized for preparation of shoe polish, cheap soaps, curds, jellies, solid
fuel of alcohol with calcium oxalate
...
When a colloid can be reversibly converted from a sol to gel and
vice versa, it is called a reversible colloid, e
...
, solution of gelatin can be reconverted into sol by
heating
...
g
...

(v) Zeta potential
...

The charge is embedded in the colloidal particle and an equivalent amount of opposite
charge remains outside and these two layers form a double layer
...

–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–

Fixed

+
+

zeta pot
...
12
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH12-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

288

bl

Hence, there is a potential difference between the particle and the medium
...

y
...
Impure water is treated with alum
...

(ii) Purification of polluted air
...
, polluted air
...
Air is passed
through Cottrell precipitator where the charge is neutralised and carbon settles down
while the hot air passes out through chimney
...
Sewage contains charged dirt particles, which is
passed through tanks fitted with oppositely charged electrodes
...

(iv) Leather tanning
...

(v) Laundry
...

(vi) Medicine
...
Blood coagulation
is effected with alum or FeCl3
...
Different types of colloidal systems and emulsion are used in cosmetics
...
Noble metals are detected by formation of their colloidal solutions and
observing their colours
...

(x) Delta formation
...

Highlights:

Dimension of colloidal particles range from 104 to 107 cm
...

Brownian motion
...
The motion is rapid for smaller
particles and also for a less viscous medium
...
When a beam of light is passed through a colloidal solution, the
path of light becomes illuminated due to the scattering of light by the colloidal
particles
...

Schulze-Hardy Law
...
This is called Schulze-Hardy law
...
It is the minimum weight in mg of a protective colloid, which when
added to 1 ml of standard gold sol (containing 0
...
0058% gold) also containing
1 ml of a 10% NaCl solution to just prevent its coagulation
...
The phase in which the emulsifier is more soluble becomes the
outer phase
...
blogspot
...
PM5

288

...

Q
...
Describe a colloidal system
...
A colloidal system is a two-phase heterogeneous system in which one phase is
dispersed in a fine state of subdivision (from 1 to 50 mµ) in another medium termed the
continuous or dispersion medium
...

Particles of colloidal system have dimension in the range from 10 to 1000 Å
...
2
...
Sol is a colloidal solution of a solid dispersed in a liquid medium whereas emulsion
is a liquid dispersed in another immiscible liquid in the form of droplets
...
3
...
Large particles of the colloid solution do not settle down and scatter the light
falling on the solution, whereas in true solution there are no such particles
...
4
...

Ans
...

Q
...
Explain the action of gelatin as protective colloid
...
Gelatin is a lyophilic colloid and when it is added to lyophobic sol, it forms a very
thin protective shell, surrounding each particle of the lyophobic colloid and protects the
penetration of oppositely charged ions, which neutralize the charge and precipitate the lyophobic
colloid
...
6
...

Ans
...

Q
...
Which of the following electrolytes will be most efficient for the
precipitation of As2S3 sol and why?
(i) KCl
(ii) CaCl2
(iii) AlCl3
...
blogspot
...
PM5

289

sp

289

COLLOIDS

...
9
...
See page 288
...
8
...

Ans
...

y
...
As2S3 sol is a negatively-charged sol and it can be precipitated by positively charged
ions of the added electrolyte
...
Since Al3+ possess highest positive valency, AlCl3 will be the most efficient
electrolyte to ppt As2S3 sol, as per Schulze-Hardy rule
...
10
...

Ans
...

lu

Q
...
Mention some important applications of colloid chemistry to industries
...
See page 288
...
13
...

Ans
...

ca

Q
...
Differentiate between lyophilic and lyophobic solutions
...
See page 279
...
14
...
The pH of the medium at which the dispersed colloidal particles are neutral and
hence do not migrate when an electric field is applied to the colloidal solution
...
15
...
If a sol is filtered through an ordinary filter paper, the colloidal particles will pass
through the pores of the filter paper since the pore-size of ordinary filter paper is larger than
the size of the colloidal particles
...

2
...

(b) Brownian movement
...

3
...

4
...

5
...

State Schulze-Hardy rule and explain with an example
...

OBJECTIVE QUESTIONS

The sizes of the colloidal particles fall in the range

(a) 102 to 104 cm
(c)
2
...

Light passing through a colloidal solution is
(a) Reflected

(b) Absorbed completely

(c) Scattered
...
blogspot
...
PM5

290

...

(c) KCl
...

rs

ve

ni

lu

ca

ht
tp
:/
/k
er
al
a

11
...

lo

8
...

ch

6
...

The random zig-zag movement of colloidal particles in a dispersion medium is called
(a) Tyndall effect
(b) Brownian movement
(c) Dialysis
...

Haemoglobin in blood is
(a) Hydrophobic colloid
(b) Hydrophilic colloid
(c) Gel
...
This can be demonstrated by
(a) Peptization
(b) Electrophoresis
(c) Dialysis
...

Milk is an emulsion of
(a) Casein dispersed in water
...

(c) Fat globules dispersed in water
...

(c) The phase in which the emulsifier is more soluble is the outer phase
...

te

5
...

4
...

http://keralatechnologicaluniversity
...
com
C-8∴N-ENGCHE∴ECH12-1
...
c
ot
sp
og
bl

it

y
...
In the d-block series from scandium (1s2 2s2 2p6 3s2 3p6 3d1 4s2) to zinc (1s2
2s2 2p6 3s2 3p6 3d10 4s2), the definition holds good for all the element excepting scandium and
zinc
...
Zinc is excluded because all its compounds
are in the +2 state
...

Transition metals have a number of common features
...

All form compounds in more than one oxidation states
...

All form a variety of complex ions
...

Many transition metal salts are paramagnetic because of the presence of unpaired
electrons in the partially-filled inner d-energy levels
...
13
...

It is to be noted that Sc and Zn form ions in one oxidation state i
...
, + 3 and + 2,
respectively
...

292

http://keralatechnologicaluniversity
...
com

...

bl

A double salt is formed generally when molar proportions of a monovalent cation
sulphate solution in water is mixed with trivalent cation sulphate solution in water and
evaporated to remove excess water, and the salt crystallises as X2SO4Y2(SO4)3
...
Another important double salt is Mohrs salt,
(NH4)2 SO4
...
6H2O
...
The double salt is characterised by complete dissociation in
solution and gives the reactions of all the ions formed by the salts in solutions, viz
...
Al2(SO4)3
...

A complex salt does not give all the ions of its constituents in solution
...

FeSO4 + 2KCN = Fe(CN)2 + K2SO4
Fe(CN)2 + 4KCN = K4[Fe(CN)6]
The solution of K4[Fe(CN)6] does not respond to the tests for Fe+2 or CN ions, but responds
to a test for a new ion [Fe(CN)6]4 (ferrocyanide ion)
...
So, it can be said, the complexions, like ferrocyanide ion, are
quite stable in the solid state as well as in solution
...

no

Examples of complex salts

ch

[Ag(NH3)2]Cl
[Cu(NH3)4]SO4

te

K[Ag(CN)2]

[Ag(NH3)2]++ + Cl
[Cu(NH3)4]++ + SO4
K+ + [Ag(CN)2]

ht
tp
:/
/k
er
al
a

Instability Constants of Complex Salts
The dissociation of a complex ion, like ionisation of weak electrolyte, follows the law of
mass action
...

Kins =

Complex ions

[M + ] [L− ]
[ML]
Instability constant

[Ag(NH3)2]+

Ag+ + 2NH3

6
...
0 × 1021

[Cu(CN)4]3

Cu+ + 4CN

5
...
4 × 1017

Werners Theory for Formation of Complex Compounds
Werner put forward a theory for the formation of complex compounds
...
The postulates of his theory may be summarised as follows:
• Metals possess two types of valencies: (i) Primary or principal or ionisable valencies
(ii) Secondary or subsidiary or non-ionisable valencies
...
blogspot
...
PM5

293

sp

293

TRANSITION METAL CHEMISTRY

...

bl

• Every metal atom has a fixed number of secondary valencies or co-ordination number
(C
...
The maximum number of ions or molecules thereby the central atoms could
form co-ordinate bonds is known as co-ordination number (C
...

Ligands

rs

it

The ions or molecules thus attached to the central metal atom by co-ordinate
bonds are called ligands
...
depending
upon the number of co-ordination centres in the ligand
...
N
...
N
...

gi

ca

• Primary valencies of the metal are satisfied by negative ions, but secondary valencies
may be satisfied by negative groups (CN , Cl, etc
...
)
or even sometimes some positive groups
...
N
...

no

lo

• The secondary valencies are directed in space about the central metal ion
...
N
...
Again, for metals, with C
...
= 4, the four such valencies are either
directed to the apices of a regular tetrahedron or a square (planar)
...
Werner could isolate even optical isomers
...

Chelate Compounds

ht
tp
:/
/k
er
al
a

Chelate compounds are complex compounds containing a ring structure in which a ligand
molecule or ion forms more than one dative covalent bonds (co-ordinate bonds) with the central
metal ion
...
Chelation increases the
stability of co-ordination complex i
...
, chelate complexes are generally more stable than
complexes formed by monodentate ligands
...
This type of ligands are known as complexones
...

++

Chelate complex with en

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH13-1
...
c
ot
og

O

bl

CO

CH2

+2

it

M

y
...
13
...

lu

It is to be noted in chelate complexes that the rings formed are five or six membered
...
They form very stable cyclic complexes, which have very low
solubility in water but high solubility in organic solvents
...
e
...
Such non-electrolytic cyclic complexes
are known as inner metallic complexes or simply inner complexes
...

ht
tp
:/
/k
er
al
a

(i) In naming cationic complexes like [Co(NH3)5Cl]Cl2, the name of the cation is considered first and then the name of the anion
...

(iii) If the complex compound is non-ionic (neutral) the name of the complex compound
like [Pt (NH3)4Cl2]0 is written as one word
...

Naming of the ligands
Neutral ligands
(C2H5)3N

Triethylamine

CO

Carbonyl

NH2-NH2

Hydrazine

CS

Thiocarbonyl

CH3NH2

Methylamine

H2O

Aquo or aqua

NO

Nitrosyl

NS

Thionitrosyl

Dimethylamine

NH3

Amine

(CH3)2NH

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH13-1
...
c
ot
og

ENGINEERING CHEMISTRY

bl

Anion ligands

Fluoro

CH3COO

Acetato

Br

Bromo

NH 2

Imido

Cl

Chloro

OH

Hydroxo or hydroxyl

I

Iodo

S2

Thio

NH2

Amido

CN

Cyano

NC

Iso-Cyano

NO2

ONO

Nitrito

SCN

S2O32

Thiosulphato

NO3

lu

ni

ve

rs

it

y
...
These ligands can co-ordinate to the metal atom through any of the
their donor atoms
...
their number is
indicated by di- for two; tri- for three; tetra- for four before the names of the ligands
...
The name of the ligands or organic molecule
is written in the bracket
...

Order of Naming the Ligands
If the co-ordination sphere of a given complex compound contains various types of ligands,
these ligands are named alphabetically
...

For anionic complexes the name of central metal atom ends in ate and the oxidation
state of the metal is written in Roman numerals (0, I, II)
...
blogspot
...
PM5

296

...

og
bl
y
...

3
[Co(Cl)6]
Hexachloro cobaltate (III) ion
...

Tetraaquodichloro chromium (III) cation
...
For example
1
...

2
...
(en)2

(SO4)2

is named as:

lo

(en)2
...

3
...

Isomerism in Metal Complexes
Isomerism in complex molecules arises due to difference in attachment of the groups or
ions to the central metal iron or due to their different spatial arrangements about the central
metal ion
...

(i) Structural isomerism
...

(ii) Stereoisomerism or space isomerism
...
This is of two types:
(a) Geometrical or cis-trans isomerism
(b) Optical or mirror image isomerism
...
For example, the complex
[Co(NH3)5 Br]SO4 (I) gives white precipitate of BaSO4 when treated with BaCl2 solution and indicates
that SO42 ion is outside the co-ordination sphere
...
blogspot
...
PM5

297

sp

297

TRANSITION METAL CHEMISTRY

...

(White)

y
...
(en)2
...
(SCN)]Cl

lu

[Co(en)2
...
Cl]SCN and

ve

[Pt(NH3)4Cl2]Br2

Linkage Isomerism

no

lo

gi

ca

This type of isomerism is exhibited by those molecules in which the ligands can coordinate with the central metal ion either of its two atoms
...
The complexes with NO2 ion as with
ligand NO2 may get attached to the central metal ion either through O-atom or N-atom acting
as donor
...
With S2O32 acting as ligand the central ion may be coordinated with the ion
either through S-atom or O-atom
...
e
...
13
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH13-1
...
c
ot
og

sp

299

TRANSITION METAL CHEMISTRY

y
...

(ii) [Co(en)3]3+ [Cr(C2O4)3]3 and [Co(en)2(C2O4)]+ [Cr(en)(C2O4)2] are co-ordination
isomers
...

Thus, propane-1,2-diamine (pn) and propane-1,3-diamine (tn) also called trimethylene diamine
have the structures:

They form isomeric complexes as [Co(pn)2Cl2]Cl and [Co(tn)2Cl2]Cl

ca

Hydrate Isomerism

no

Geometrical Isomerism

lo

gi

Water molecule is a very effective co-ordinating agent and may replace NH3, Cl2 etc
...
Hydrate
isomers are generated due to variation in number of water molecules in the co-ordination
sphere
...
6H2O are
[Cr(H2O)6]Cl3; [Cr(H2O)5
...
Cl2
...
Cl2]
...
2H2O

ht
tp
:/
/k
er
al
a

te

ch

Geometrical isomerism originates due to the different arrangements of the co-ordinated
groups in space around the central atom in a definite geometrical pattern
...
The number of
possible isomers is different for these two spatial arrangements
...
13
...

NH3

NH3

H3N

NO2

O2 N

NH3

Co

Co

H3N

NO2

H3N

NH3
(a) cis-form

NO2
NH3
(b) trans-form

Fig
...
4

Diamine dichloro platinum [Pt(NH2)Cl2] exists in two isomeric forms (Fig
...
5)
...

Cl

Cl

NH3
Pt

Pt
NH3

Cl

NH3

H3N

(a) cis-form

Cl
(b) trans-form

Fig
...
5

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH13-1
...
c
ot
og

ENGINEERING CHEMISTRY

Optical or Mirror Image Isomerism

y
...
13
...
7
...

en

rs

it

Mirror plane

en
Cl

Cl

Cl

ni

Cr

ve

Cl

Cr

en

lu

en

(b)

ca

(a)

C6H4COO

–

(–)

OOCH4C6

lo

As

gi

Fig
...
6

H3C

S

no

H5C2

CH3
As

S

(a)

C2H5
(b)

Mirror plane

ch

Fig
...
7 Optically active arsenic compound with co-ordination number 4
...
These are: (i) Valence bond theory, (ii) Crystal field theory, (iii) Molecular orbital
theory and (iv) Ligand field theory
...

Valence Bond Theory
This theory was developed by Pauling and deals with hybridisation of the complex
...

• The empty orbitals of the metal ion hybridise to give an equal number of equivalent
hybrid orbitals
...

...
This overlapping results in a σ-bond or possibly a π-bond
...
blogspot
...
PM5

300

sp

300

...

3d

y
...
The complex formation is
as follows:
4s

4p

6

it

(a) Electronic configuration of Iron in
2

ground state (
...
4s )
6

2+

rs

(b) Electronic configuration of Fe
0

ve

ion in ground state (
...
4s )
2+

(c) Electronic configuration of Fe ion in
2

3

ni

d sp hybridised state
2+

(d) Electronic configuration of Fe ion in

×× ××

lu

[Fe(CN)6]

4–

–

–

CN

×× ×× ××

–

–

–

CN CN CN

–

ca

CN CN

××

no

lo

gi

The ground state electronic configuration of Fe is
...
In Fe2+ ion, the two 4s
electrons move out leaving 4s orbital vacant
...

ch

The shape of the complex molecule is octahedral and due to the absence of unpaired
electrons, the complex is diamagnetic
...
So, this is often
called inner orbital complex
...

ht
tp
:/
/k
er
al
a

te

Another example of sp3d2 configuration is [FeF6]3 complex
...
3d 4s )

3 2

sp d

3d

4d

Electronic configuration of
3+

Fe

3 2

in sp d configuration
3 2

sp d

Electronic configuration of
3+

4d

×× ×× ×× ×× ×× ××

3–

Fe ion in [FeF6]
configuration

–

F

–

F

–

F

–

F

–

F

–

F

3 2

Six sp d hybridised orbitals
having lone pairs of electrons
–
donated by six F ligands
...
Because of presence of five lone electrons in 3d level the compound is
highly paramagnetic and often referred to as sp high spin complex
...
blogspot
...
PM5

301

sp

301

TRANSITION METAL CHEMISTRY

...

As is implied the tetrahedral complexes are sp3 hybridised
...
Atomic
number of Ni is 26
...
The co-ordination of nickel is
four
...
On the basis of VBT [Ni(NH3)4]2+
is formed as follows:
3d

4s

8

2

in ground state (
...
13
...

NH3

2+

Ni

NH3

H3N

NH3

Fig
...
8 Tetrahedral shape of [Ni(NH3)4]2+ ion resulted from sp3 hybridisation
...

Square Planar Complexes
These are formed by dsp2 hybridisation
...
The formation of the
complex is shown below:

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH13-1
...
c
ot
4s

og

3d

4p

in ground state
dsp

y
...
The
shape of [Ni(CN)4]2 is given below in Fig
...
9
...
13
...

CRYSTAL FIELD THEORY (CFT)

The postulate of this theory is: bonding between a central metal ion and its ligands simply
arises from purely electrostatic force of attraction
...
If the ligand (Ln) is neutral molecule (L) the negative end of the dipole is attracted
towards the central positive metal ion
...

Crystal Field Splitting of d Orbitals
This theory considers only the effect of the ligands on the energy of outermost
d-electrons in the central metal ion
...
e
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH13-1
...
c
ot
bl

eg
Do or 10 Dq

y
...
6 Do

t2g

dxy dyz dzx

dxy dyz dzx
(b)

(c)

ve

(a)

it

– 0
...
13
...
(a) The five degenerate d-orbitals in
the isolated central metal ion
...
(c) Crystal field splitting of d-orbitals into t2g and eg sets by electrostatic
field of the six approaching ligands
...
13
...
When the six ligands approach the central metal atom along the axes
they exert an electrostatic force of repulsion on the d-electrons of outermost shell i
...
, the
d-electrons are repelled by lone pair of electrons of the ligands
...
13
...
Since the lobes of dz2 and dx 2 − y2 orbitals called as eg set of
orbitals fall directly at the path of the approaching ligands, the electrons in these orbitals
experience a greater force of repulsion exerted by the electrons of the ligands than that by the
electrons of the dxy, d y and dzx orbital called as t2g set of orbitals which are directed in space
2

ht
tp
:/
/k
er
al
a

te

ch

along x, y and z axes
...
The separation of five dorbitals in the t2g and eg sets of different energy states is known as crystal field splitting
...
∆o is called crystal
field stabilisation energy (CFSE)
...
4∆o while that of eg set is increased by 0
...
13
...

Strong and Weak Ligands

Strong ligands can split the five d-orbitals into t2g and eg sets strongly i
...
, there splitting
power is high whereas the weak ligands can split the set of orbitals weakly i
...
, there splitting
power is weak
...
The following is the arrangement of ligands with the splitting power of increasing order
...

C-donor > N-donor > O-donor > X-donor
Examples of C-donor = CN
N-donor = NO2, NH3
O-donor = H2O, OH
X-donor = F > Cl > Br > I
Distribution of d-electrons in t2g and eg sets of orbitalslow spin and high spin
complexes
...
e
...
blogspot
...
PM5

304

sp

304

...

bl

spin s is also reduced
...
These types of complexes
are known as low spin (L
...
) or spin paired complexes
...
e
...
Thus weak ligands produce higher number of
unpaired electrons and so the higher value of s
...
S
...

ve

rs

Table 13
...
The complexes having no unpaired
electrons should not exhibit any magnetic property, so therefore are diamagnetic
...
The magnetic moment µ is related to the unpaired electrons n by the relation
µ = n(n + 2)
...
2: Distribution of d-electrons in t2g and eg sets in weak octahedral ligand field
Distribution of d-electrons in

dx ion

t2g set

eg set

d1

↑

_

_

d2
d3
d4
d5
d6
d7
d8
d9
d10

↑
↑
↑
↑
↑↓
↑↓
↑↓
↑↓
↑↓

↑
↑
↑
↑
↑
↑↓
↑↓
↑↓
↑↓

_
↑
↑
↑
↑
↑
↑↓
↑↓
↑↓

↑
↑
↑
↑
↑
↑↓
↑↓

_
↑
↑
↑
↑
↑
↑↓

n

S = n/2

1

1×

2
3
4
5
4
3
2
1
0

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH13-1
...
c
ot
og

ENGINEERING CHEMISTRY

Application of Ligands

bl

Ligands are widely used in different fields of chemistry
...

(i) In gravimetric analysis
...

Cupferron gives a precipitate with ferric ion in acid medium
...

Dimethylglyoxime

ni

Cupferron (ammonium salt of nitroso
phenyl hydroxylamine)

lu

(ii) In qualitative analysis
...

ca

H2N C  C NH2
 
 
S S

gi

Rubeanic acid

no

lo

(iii) In complexometric titrations
...
, are
estimated by complexometric titration
...
Some metal ions like
zirconium and hafnium can be separated from solution by chelation with
thionyltrifluoro-acetone (TTA)
...
g
...

(v) For medicinal purpose:
(a) EDTA is used to inhibit heavy metal poisoning
...

(c) Vitamin B12 itself is a chelate compound in which the central metal ion is cobalt
...

SHORT QUESTIONS
1
...

3
...

What are transition metals?
Mention the common features of the transitional metals
...

Differentiate between double salt and complex salt
...
blogspot
...
PM5

sp

306

306

...

3
...

5
...

7
...

it

rs

ve

ni

lu

ca

gi

lo

EXERCISES

State the postulates of Werners co-ordination theory and discuss the structure of K4Fe(CN)6 on
the basis of this theory
...

Discuss the geometrical as well as optical isomerism in complexes with co-ordination number 4
and 6
...
On the basis of this theory predict whether the complexes [CoF6]3 and [Co(NH3)6]+3 are paramagnetic or diamagnetic
...

Cite some fields of application of ligands in our daily lives
...

te

ch

14
...

16
...

18
...

20
...

22
...

24
...

26
...

Give main postulates of Werners theory
...

What are chelate compounds? Give examples
...

Give an example of bridging ligand complex
...
Give one example of each type
...

Give the state of hybridisation of a square planar complex
...

Calculate the magnetic moment µ for one unpaired electron
...
1
...

[Ans
...
83; 3
...
9; 5
...
93 and 7
...

6
...

8
...

10
...

12
...

sp

307

TRANSITION METAL CHEMISTRY

(a) CoCl2
...

( f ) [Cr(H2O)5 Cl]2+
( g ) [Cr(H2O)4 Cl2]+ (h) [Cr(H2O)6]Cl3
(i) [Pt(NH3)4Cl2]Br2 ( j ) [Pt(NH3)4 Br2]Cl2 (k) [Co(NH 3)4Cl2]NO2
8
...

(b) Ammonium diamine tetrathiocyano chromate (III)
(c) Triamine aquo dichloro cobalt (III) chloride
(d) Sodium hexa nitrito cobaltate (III)
...
blogspot
...
PM5

307

IV

Co (en)2

...

14

ni

INTRODUCTION TO THE STUDY OF METALS

ve

rs

Metallurgy

ca

lu

The gold and silver among the metals are probably the first used by man
...
C
...

lo

gi

Today we find the metals are very extensively used in art and industry
...
Copper is another important metal being used mainly in electrical articles
...

Metals

ch

no

Metals are the elements, which occupy the left hand side of the periodic table with one,
two or three electrons in the outermost shell that takes part in bonding and chemical
reactions
...

• Good conductors of heat and electricity
...

• Generally solids are with high m
...
and b
...
(only six metals melt below 100 °CHg
which is a liquid and four group I metals: Na, K, Rb, Cs)
...
e
...

• Form basic or amphoteric oxides
...

The more an element exhibits these properties, the greater is its metallic character
...
Each metal atom in a metal crystal
contributes electrons from its outermost shell to form a sea of delocalised electrons
...
When a metal atom looses
electron it becomes positively charged
...

308

http://keralatechnologicaluniversity
...
com

...

+
–
+

–
+
–

rs

Fig
...
1 Simplified picture of metallic bonding
...
Metals can bend without breaking because metallic bonding is not highly
directional
...

lu

Mineral Resources of India

no

lo

gi

ca

The sound economy of a country depends upon its mineral wealth
...
Iron ores occur abundantly in India
...
The next important mineral is manganese
...
Copper is chiefly found in
Chotanagpur and Sikkim
...
Chromite is found in Mysore
and Orissa
...
Borax, kaoline,
limestone, gypsum, pitch-blende, monazite sand are other minerals, which are found in India
...
A metal is said to occur native or
free when it is found in nature in the metallic state
...
We can say that these metals are not readily attacked by the
moisture, oxygen, and carbon dioxide of the air
...
These
metallic compounds generally occur in the form of hard stones either in the underneath or in
the earth surface
...
Minerals are always associated with sand, soil or other impurities
...
The percentage of gangue in a mineral is always higher than the mineral
itself
...
2H2O] for Calcium

• Nitrate

[Chile saltpetre, NaNO3] for Sodium

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH14-1
...
c
ot
sp
og
bl
y
...
blogspot
...
etc to
eduktu@gmail
...
blogspot
...
c
ot
[Fluospar, CaF2] for calcium

• Silicate

[Mica, KHMg2Al2(SiO4)3] for Magnesium

bl

• Halide

og

ENGINEERING CHEMISTRY

y
...
2SiO2
...
H2O)

Oxides and

(iv) Pyrolusite (MnO2)
Braunite (Mn2O3)
(v) Chromechre (Cr2O3 )

(vi) Tin stone or cassiterite (SnO2)
(vii) Felspar (K2O
...
6SiO2 )
Copperglance (Cu2S);
Copperpyrite (CuS, FeS)
Zinc blende (ZnS)
Galena (Pbs)
Cinnabar (HgS)
Stannite (Cu2S, FeS, SnS2 )
Iron pyrite (FeS2 )
Silver glance (Ag2S);
Rubby silver 3Ag2S
...
MgCO3)
Magnesite (MgCO3);
Dolomite (MgCO3CaCO3)
Manganese spar (MnCO3)
Cerussite (PbCO3 )
Calamine (ZnCO3 )
Gypsum (CaSO4
...
24H2O)

(iv) Barium IIA (Alkaline earth metal)

Heavy spar (BaSO4)

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH14-1
...
c
ot
og

Epsomite (MgSO4
...
H2O)
Rocksalt (NaCl)

(ii) Potassium

Sylvine (KCl)

y
...
Ca3(PO4)2 )

Carnallite KCl, MgCl2 6H2O

ve

(v) Magnesium

ni

(vi) Aluminium
(i) Sodium
Silicates

lu

(ii) Potassium
(iii) Zinc

ca

(iv) Aluminium

Cryolite (3NaF, AlF3 )

Sodium silicate (Na2SiO3 )

Felspar (K2O
...
6SiO2)

Willemite (ZnSiO2)

Felspar (K2O
...
6SiO2)

gi

Ores

ch

no

lo

Generally all minerals cannot be considered important for extraction of metal from them
...

Particularly, the minerals from which metals can be extracted easily and cheaply
are known as ores
...

Metallurgy

ht
tp
:/
/k
er
al
a

te

The process by which the metals are extracted from their respective ores is
known as metallurgy
...

Concentration of the Ore

Almost all ores are associated with gangue or matrix
...
As a matter of
fact, the ore is enriched with the desired metallic compound
...
There are several processes of the concentration of
ores, which are described below
...
The main steps for the extraction of metals are generally as follows:
1
...
Concentration of the ore
3
...
Reduction
5
...
This is one of the crucial steps of concentration process
...
, Jaw crusher, Gyratory crusher etc
...
This is effected in grinding and pulverising mills
(Figs
...
2 and 14
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH14-1
...
c
ot
Lumps (ore)

it

y
...
14
...

ni

Fig
...
2 Crushing
...
This process includes all methods of concentrations in which water in motion is used
...

lo

gi

(ii) Floatation
...
Sulphide ores, as a rule, do
not get wet as do silica and most oxides when treated with water
...

ht
tp
:/
/k
er
al
a

te

ch

no

(iii) Oil floatation process
...
Oils form a film over the sulphide ore
...
Generally some xanthates are used with
pine oils
...
A foam is produced and floats along with the sulphide ore over the surface of
water
...
The concentrated ore is collected from
foam (Fig
...
4)
...
14
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH14-1
...
c
ot
og

sp

313

METALLURGY

y
...
Ferromagnetic ores can be separated by passing the ore through
a strong magnetic field, whereby ferromagnetic substances are separated from the
ore
...

Crushed ore

it

Non-magnetic
particles

ca

lu

Rubber belt

ni

ve

rs

Magnet

gi

Magnetic particles

Fig
...
5 Magnetic separation
...
These two terms are used, somewhat interchangeable, among
the metallurgists, though a distinction exists between them
...
e
...
The term is usually applied in case of oxidising the ores
...

2MS + 3O2 = 2MO + 2SO2

ht
tp
:/
/k
er
al
a

MS + 2O2 = MSO4
• Calcination: To calcine a material is to heat it very strongly but at a temperature
insufficient to melt it; with a view to driving of volatile matters leaving some pores
on the rocky ore to facilitate the reduction process, so that reducing gas viz
...
As for example,
∆

M2O3
...
They are often refractory in nature
and remain unfused which may disturb efficient extraction of the metal
...
They become easily fusible when heated with other substances, those substances are
known as fluxes
...

heat

Gangue + Flux → Slag (fusible)

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH14-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

314

Selection of Flux

rs

it

y
...
If it is acidic, basic flux is
to be used viz
...
If the gangue is basic in character, then an acid flux like sand
(SiO2) must be employed
...
Large scale industries, like metal extraction, need
economy of fuel consumption
...
This is a special type of furnace much used in metallurgy
...
14
...

no

Chimney

te

ch

Hearth

ht
tp
:/
/k
er
al
a

Ore

Air
Flame fuel

Fig
...
6 Reverberatory furnace
...
It is a type of furnace consisting of an enclosed chamber, made of
refractory materials, from which the fuel and its products of combustion cannot come
in contact with the materials heated in it (Fig
...
7)
...
14
...

• The other furnaces are blast furnace (for iron extraction), open hearth furnace (for
steel manufacture) and electric furnace (for Phosphorus extraction)
...
blogspot
...
PM5

314

...

Limestone (CaCO3), ore (Fe2O3)
& cock are added at the top
Cone

rs

it

Charging
holes

ve

250 °C
2Fe2O3 + CO ® 2Fe3O4CO2

Waste gases exit

ni

Fe3O4 + CO ® 3FeO + CO

Upper zone (250 °C–700 °C)

FeO + CO ® FeO + CO2
Spongy iron

Tuyer for hot air
(form Cowper’s Stoves)

gi

Fe Metal & Mixed with
C2P4Si2Mn etc
...
14
...

Feed hopper

P & CO

Coke, sand & rock
CO
Carbon electrodes

Fig
...
9 Electric arc furnace
...
The process by which a metal is extracted in the fused state is called smelting
...
blogspot
...
PM5

315

...
It is the operation of joining the two pieces of a metal either by pressure or by
fusion to one compact mass
...

Alloy
...
When one of
these metals is mercury, the alloy is called an amalgam
...
Steel is an alloy of iron and carbon, a non-metal
...
Controlling the composition of an alloy makes
it possible to vary its properties
...
g
...
Whereas ferrous alloys always contain iron as one of the
constituents of the alloys, e
...
, Stainless steel contains Fe, Ni, Cr
...

lo

• to lower the melting and boiling points of individual metal
...
Component metals are mixed together in the desired ratio and melted
followed by cooling
...
Finely divided metals are compressed in the desired ratio
...

ht
tp
:/
/k
er
al
a

Examples of important alloys are
• Mild steel
...
1-0
...
It is relatively cheap, can be easily
rolled into sheets, and can be pressed into shape
...
It is mainly used in making
utensils as well as reactors in industries
...
It is used in making rolls
...

• Wrought iron (C = 0
...
25%), is mainly used in making household furnitures
...

• Brass, an alloy of copper (Cu:Zn = 60:40), has a gold colour and does not corrode
...

• Solder
...

• Duralumin
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH14-1
...
c
bl

• Alnico
...

y
...
This
process is called cementation and the powder is called the cement
...
, are obtained in nature in the free state
...

ca

lu

• But, most of the metals occur as their compounds such as oxides, hydroxides, carbonates,
sulphides, halides etc
...

lo

• When the ore is an oxide, hydroxide, or carbonate it is first calcined to get porous oxides
and then the calcined ore is reduced to the metal, generally, by carbon reduction
process
...

ch

no

• When the ore is a sulphide, it is first heated in the presence of air i
...
, roasted to get
metallic oxide and then reduced to get the metal
...

Methods of Reduction of the Processed Ore
Metal extraction involves two main types of processes for the reduction of the metallic
compounds
...
blogspot
...
PM5

317

sp

ot
• Magnalium
...

og

317

METALLURGY

...

y
...

(b) Chemical reduction by coke at high temperatures (for example, iron, lead)
∆

rs

it

MO + C → M + CO
(c) Chemical reduction by a more reactive i
...
, electropositive metal (for example,
chromium and titanium extraction)
...

lu

(a) Electrowinning at low temperature in solution in water (for example, Zn extraction
for ZnSO4 solution)
...
The combination of
oxygen with aluminium at that temperature evolves much heat, which is utilised in Goldschmidt
Thermit process or Aluminothermic process for the reduction of metallic oxides e
...
, MnO2
or Cr2O3 and for the separation of molten metals
...
14
...
Thermite, a mixture of aluminium powder and iron oxide in the
ratio 3:1 by weight, is ignited in a crucible by a ribbon of magnesium, when a violent reaction
takes place producing molten iron at 2500°C
...

Fig
...
10 Goldschmidt Thermit process
...
blogspot
...
PM5

318

...

bl

Almost all metals obtained by reduction processes contain some impurities
...
The purification processes are:
1
...
Electro-refining
1
...
The impure metal is melted and a stream of air is
purged through the bottom, as a result of which the easily oxidisable impurities are
converted to oxides
...

lo

gi

ca

lu

• Fractional distillation
...
The crude zinc, which is known as spelter, contains about 2% of lead and
traces of iron, cadmium, arsenic as impurities
...
When zinc together
with cadmium distils over leaving behind lead (b
...
1620°C) and iron (b
...
2800°C)
...
e
...
p
...
9% of zinc is left in the retort
...
An easily fusible metal such as tin or lead can be refined by this process
...
14
...

Impurities

ing

op

Sl
he
ar
th

ht
tp
:/
/k
er
al
a

te

Impure metal

Furnaces

Pure molten
metal

Fig
...
11 Refining of metal by Liquation
...
14
...
This process of purification is employed effectively in some
special cases
...
The actual process is: a narrow rod of impure metal is
taken and a small portion of it at one end is almost melted by application of heat
...
At last the molten zone containing all the impurities

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH14-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

320

bl

reach the other end
...
The remaining portion of the rod consists of the pure metal
...

Molten zone

Resolidified
portion

Most impure
zone to be
cut out

ni

ve

Source of heat

Fig
...
12 Zone refining
...
Electro-refining
...
Usually an electrolytic cell is set up using
thin sheets of pure metal as the cathode and comparatively thick impure metal slag as anode
...
During electrolysis, pure metal
from the electrolyte gets deposited on the cathode and the equivalent amount of metal from the
anode passes into the solution
...
This deposit is known as anode mud
...
A typical example of electrolytic refining is of copper (Fig
...
13)
...

H2SO4 as
electrolyte

Impure Cu anode

Pure Cu cathode

Fig
...
13 Electrolytic refining of copper
...
14
...
In this technique, the metal powders or alloy constituents are compacted in a
die with melting or no melting followed by sintering
...

The article is made into the desired shape by powder metallurgy in the following steps:
(i) Pulverisation of metallic powders
(ii) Mixing and blending
(iii) Compacting
(iv) Pre-sintering, and
(v) Sintering
(vi) Finishing operation
...
blogspot
...
PM5

320

...

bl

(i) Pulverisation of metallic powders
...
For
pulverisation ball mills can be employed
...
This method requires control of pressure and temperature and the
oxidation of metal into an atmosphere of inert gas
...

(c) Chemical:
1
...
By decomposition,
∆

lo

gi

ca

Ni(CO)4 → Ni + 4CO↑
The metals are obtained in a state of fine powders in both cases
...
This operation is required when a combination of metallic
powders are used
...
Lubricants may be
added if necessary
...
The metal powder in right proportions is then taken in a die into the
cavity (female joint) of accurate dimensions and then compressed (1001000 N/m2) by
the male joint of the die
...

(iv) Pre-Sintering
...
This step increases the strength of green compact as well as
removes the lubricant if used
...

High
pressure

Guide pins

Top moulding part
(Male joint)
Bottom moulding part
(Female joint)

Alloy ingredients
Extraction pin

Fig
...
14 Technique of powder metallurgy adopted in a die
...
Compacted pieces are heated to a temperature below and very close to the
melting point of the metal in a furnace, preferably in an atmosphere of hydrogen,
whereby metal particles sinter to a coherent mass
...

(vi) Finshing operations
...
, to get accurate shape of the work pieces
...
blogspot
...
PM5

321

...

(i) Porous bearings ; (ii) Tungsten filaments for electric bulbs ; (iii) Sewing machines
(iv) Gears ; (v) Clutches, breaks etc
...

ni

ve

(ii) Clean and smooth operations
...

ca

lu

(iv) Articles with impregnated lubricants can be produced which would be self-lubricating
for ever
...

Disadvantages

gi

(i) Dies of desired precision are required which are very much expensive
...

no

SOME SPECIFIC EXAMPLES OF EXTRACTION OF METALS

ch

Titanium (Ti)

ht
tp
:/
/k
er
al
a

te

Titanium is a very strong metal and has a density much less than that of steel
...
The metal is being protected like aluminium by a thin oxide
layer formed on the surface of the metal
...
3d2
...
It can exhibit three oxidation states +2, +3 and +4, but only +4 oxidation state is
common
...

Smoke grenades produce dense clouds of titanium (IV) oxide due to rapid hydrolysis of
titanium (IV) chloride
...

Among the most abundant metals in the earths crust Titanium achieves the fourth place
...

After the purification of the ore, it is heated with carbon in a steam of chlorine gas at
about 1100 K
...

The chloride of the metal is then allowed to react with molten sodium or magnesium at
800 K in an inert argon atmosphere, the reaction is exothermic and so temperature rises
...
blogspot
...
PM5

322

...

bl

The reactor is kept hot for about two days then the mass is removed from the furnace and
is allowed to cool
...
Extremely pure Ti can be obtained by decomposition of TiI4 vapour on an electrically
heated tungsten (W) filament in vacuum
...

ni

ve

(ii) Other major uses are the production of chemical components of chemical plants such
as heat exchangers
...
e
...
The commercial ore is chromite
...
The first step is to convert the ore to pure
Cr2O3
...

The exothermic reaction produces pure metal (99 %)
...
The
presence of carbon in the metal makes the metal brittle and less resistant to corrosion
...
The main use of chromium is to make alloys with iron (stainless steels)
...

Uses

ht
tp
:/
/k
er
al
a

(i) The chief uses of chromium are in the manufacture of chrome steel and chromium
plating
...

This is very hard and used in making cutting tools
...
Steels with 18% Cr and 78% Ni are superior corrosion resistant
...

(iii) Chromium plating unlike nickel plating is resistant to sulphur compounds of the
atmosphere
...
3d8
...
The common oxidation state of nickel is +2
...

Uses
(i) Nickel is so unreactive that it is used to make spatulas and crucibles
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH14-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

324

(iii) Nickel in finely divided form acts as a good catalyst in hydrogenation reactions
...

bl

(iv) It is a heterogeneous catalyst and is used to harden unsaturated vegetable oils by
addition of hydrogen across the double bond
...
3d5
...
The main oxidation states of manganese are:
the purple manganate (VII) ion, which is a strong oxidising agent in
acid medium
...

+2 as Mn2+

the pink manganese (II) ion in salts such as manganese (II) sulphate
...

(ii) The metal is mainly used in steel industry in making alloy steels and as a deoxidant
...

lo

(iv) An alloy of copper, aluminium and manganese (Heuslers alloy) is ferromagnetic
...

ch

Cobalt (Co)

te

Cobalt is a hard, shiny d-block metal and is less reactive than iron
...
3d7
...

In solution cobalt forms ions in the +2 and +3 oxidation states
...

Uses

(i) Cobalt is used in making the so called hard alloys which are superior to high speed
tool steel as regards the life of the tools
...

(iii) Cobalt may be used for electroplating iron, steel and brass etc
...
e
...

(v) Some cobalt salts with organic acids are used as driers in paints and varnishes
...
Cobalt-60 capsules are
used to kill cancer tissues by radiation
...
It occurs in the form of compounds
...
2UO3
...
3H2O
...
blogspot
...
PM5

324

...
CO3 solution

UO2Cl2

gi

Na4 [UO2(CO3)3]

Residue

BaSO4,
RaSO4,
PbSO4,
SiO2 etc
...

bl

Uranium is extracted from pitchblende and a flow diagram for the extraction of uranium
is shown below:

Filtration

UO2Cl2

Residue
(NH4)2U2O7

Ignited

Metallic U

U3O8

Carbon reduction

Uses

(i) Its principal use is as atomic fuel in nuclear reactors
...

U235 + 1 n = Ba140 + Kr92 + 200 meV
...

(iii) Uranium steels are also important technically
...
blogspot
...
PM5

325

...
Zirconium also occurs in alluvial
sands of Kerala and Sri Lanka
...

Extraction

(i) Zirconium is produced commercially by Kroll process
...
)

ve

rs

it

(ii) Van Arkel-de Boer process
...
A tungsten or Zirconium filament is heated to 1300 °C in the same vessel
...

ZrI4 = Zr + 2I2

ni

Properties

lu

Zirconium is a lustrous, silvery metal with m
...
1857 °C
...
The traces of impurities like O, N and C make the metal brittle
...
, O2, H2; when finely divided, the metal is pyrophoric
...
Despite this inherent reactivity,
the metal has got outstanding resistance to corrosion, which is due to the formation of a dense,
self-heating oxide film over the metal surface
...
The most important oxidation state of the metal
is +4
...

ht
tp
:/
/k
er
al
a

(ii) It is used in a variety of alloy steels; a notable superconducting alloy is with niobium
which retains its superconductivity even in strong magnetic fields
...
Zirconiums major
use is as a cladding for uranium dioxide fuel rods in water-cooled nuclear reactors for
its low absorption of Thermal neutrons
...
So Hf content of Zr is reduced to
less than 100 ppm
...

Define metal and mention some of its characteristics
...

What do you mean by metallic bonds? Explain electrical conductivity of metal in the light of
metallic bonds
...

What do you mean by minerals and gangue? Give relations between them
...

Distinguish between ores and minerals
...
blogspot
...
PM5

326

...

What is the concentration of ore?

7
...

8
...

bl

5
...

ve

(iv) Roasting
9
...
What is flux? State the factors on which the selection of flux is based
...
Describe different types of furnaces with their uses in metallurgy
...
Write short notes on:
(i) Smelting

ca

(ii) Welding

gi

13
...
Give the composition and uses of the following alloys:
(i) Mild steel

lo

(ii) Stainless steel

no

(iii) Manganese steel
(v) Alnico
(vi) Wrought iron

ht
tp
:/
/k
er
al
a

(viii) Brass

te

(vii) Magnelium

ch

(iv) Duralumin

(ix) Bronze
(x) Solder

14
...
Give general method of extraction of metals from their ores
...

Write notes on:

(i) Pyrometallurgy

(ii) Hydrometallurgy

(iii) Goldschmidt thermit process
(iv) Electro-refining
(v) Zone refining

17
...

18
...

19
...

20
...

21
...

(b) What is sintering in powder metallurgy?

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH14-1
...
c
ot
og

ENGINEERING CHEMISTRY

22
...
Indicate its position in the periodic table
...

y
...

23
...

24
...
(a) Write down some of the ores of uranium with chemical formula
...

lu

(c) State some uses of uranium
...
Give an account of zirconium with special reference to its important ores and one method of
extraction
...
blogspot
...
PM5

328

sp

328

...

it
rs

Adhesives

ni

ve

15

lu

Adhesives

Bonding has several advantages

gi

ca

Adhesive is defined as a material that is capable of joining bodies together by surface adhesion
and internal strength without the structures of the bodies undergoing any changes
...

ht
tp
:/
/k
er
al
a

te

ch

no

lo

1
...

2
...

3
...

4
...

5
...

6
...

7
...

8
...

9
...

10
...
g
...

11
...

Limitation and Restrictions of Adhesive Bonding
1
...

2
...

329
http://keralatechnologicaluniversity
...
com

...

bl

3
...

4
...

5
...

6
...

7
...

lu

ni

Adhesion Theories
Several different theories have been developed that explain the mechanism of adhesion
...

lo

gi

ca

Electrostatic theory explains that by contact of the adherend and the adhesive, transfer
potentials are build up which sets up an electrical double layer and the corresponding coulombic
attraction forces develop between the two components
...

The forces that are responsible for adhesion are the so called secondary valence or van der
Waals forces
...
None of the above theories explain all the aspects of bonding
...
By wetting the surface of the adherend with the adhesive, contact in
molecular dimensions takes place; when the interfacial boundary energy is lower than the
sum of the surface energies of the adhesive and the adherend, permanent adhesion occurs
...
By chemical reaction: The reactive low molecular wt
...
wt
...

2
...
The solvent gets
evaporated and thereby gelling and finally hardening takes place leading to strong bonding
between the surfaces
...
By pressure application: Tacky substances in solvent-free form adhere spontaneously
to the surfaces of most materials, only under pressure
...
By cooling: Thermoplastic materials are applied to the adherend surfaces in a molten
and hot condition which on cooling solidifies developing bonding strength
...
Smoothness of the adherend surfaces: For wood surfaces smoothness of the surfaces
adds to the bonding strength of adhesives
...
, the large number of capillaries preferentially enclose the liquid portion of the
adhesive and disturb the equilibrium distribution of the adhesive on the adherend surface
leading to weak joint formation
...
Surface tension: The wetting characteristics of an adhesive depend on its (a) viscosity
and (b) surface tension
...
blogspot
...
PM5

330

...
When this tension becomes minimum, the surface is better wetted
...

3
...
This bond
strength can be improved by applying pressure
...

rs

4
...

ve

(a) Tensile strength, shear strength and compressive strength of the film: These three
characteristics influence the bonding strength in a positive way
...
Creep rate under stressed condition
should be lower for better adhesives
...

Substance can be added to the adhesive to alter the thermal coefficient of expansion
to match with that of the adherend and hence increasing the bond strength
...
Application modes of adhesives: The mode of application of adhesive on the surface to
be joined also influences the bonding strength
...
Sufficient time is to be allowed
so that the curing time be enough to establish a strong bonding
...
Less pressure is required
in case the adherend surfaces are smooth but in the case of porous surfaces, pressure should be
applied to join the surfaces together
...
Degree of polymerization: Bond strength of the adhesive is affected by the extent of
polymerization of the monomers
...
g
...

2
...
Thus, addition of polar molecules to
the non-polar adhesives increases the adhesive power
...
Complexity of the adhesive molecule: Complexity and chain length influence the
adhesive action
...
wt
...
Similarly, in the case of cellulose esters the optimum chain length of fatty
acid is from 6 to 14 for better bond strength
...
pH: Strong acids and strong alkalies affect the bond strength of adhesives negatively
...
g
...

Technique of Bonding
Different type of adherend surfaces, different type of adhesives, differing bonding
processes give rise to different types of bonding
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH15-1
...
c
ot
og

ENGINEERING CHEMISTRY

Cleaning and Pretreatment of Adherend Surfaces

y
...

rs

it

Loose dirt and oxide layers can be removed by brushing
...
For certain plastics, pretreatment processes are used
to increase the affinity for bonding
...

ni

ve

For plastics which are difficult to bond, surfaces are modified by chemical treatment to
increase the surface tension and wettability
...

lu

For wooden surfaces, the adherend surfaces are machined to bring smoothness for better
bond strength
...
Solid adhesives are melted, very viscous
adhesives are thinned with solvent, plasticizers, catalysts, hardners etc
...

ch

no

lo

Uniform addition of calculated quantity of adhesive is required for proper bonding
strength, so the method of application is very important
...

ht
tp
:/
/k
er
al
a

(b) Thin-flowing sprayable adhesives are distributed uniformly over large areas with
spray guns (Fig
...
1)
...

(d) Highly viscous adhesives applied as coatings
...

( f ) For chemically reactive systems, one
component is the thermosetting resin,
which is applied to one surface and the
other being the catalyst applied to the other
surface to be bonded
...

b

Fig
...
1 Adhesive application by means
of a spray gun (a) Adhesive (b) Compressed air (c) Atomized adhesive
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH15-1
...
c
ot
og

sp

333

ADHESIVES

y
...

(a) For immediately drying type of adhesives the adherends are held close to each other
immediately completing the assembly
...
Thus to allow the time for evaporation of the solvent and tackiness to develop
the assembly is to be kept for a long period
...

lu

ni

(d) For chemically reacting adhesives the adherend surfaces are kept in contact and the
joint is allowed to remain for the required period to allow the chemical reaction to be
complete to obtain high bond strength
...

no

lo

(a) For slow reacting and setting adhesives the time of application of pressure is longer
to ensure completion of the chemical reaction or complete evaporation of the solvent to develop
bond strength
...
The necessary pressure is generally applied by using presses, pressure rolls
...

For warm-setting adhesives heating is required for a specified period
...
For
molten adhesive, cooling under pressure is required
...

Classification of Adhesives
Adhesives may be classified on the basis of chemical nature, setting mechanisms, adhesion
mechanism etc
...
Thermosetting synthetic resins
...
The bonding of these are moisture, heat
and fungi proof
...
This is a pressure sensitive type of adhesive
...

Use: This is available as solid, liquid or impregnated film and used for bonding wood
and metal
...
It is a transparent, syrupy compound, used in the form of
aqueous solution or spray dried powders, generally with acid hardness to improve
reactivity for bonding
...
Though this adhesive

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH15-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

334

bl

forms bond which is resistant to temperature, moisture etc
...

y
...
Bonding wood, particularly to produce plywood and chipboard, laminates, for
aircraft and in ship industries
...

it

(c) Polyesters
...
They possess good moisture resistance but low heat resistance
...
Used for making laminated glass and cloth
...
Epoxy compounds are available both in liquid and solid forms
...
Epoxy
resins are also combined with phenolic resins and poly vinyl acetate resins and used
as adhesion promoters
...

It can also be cured without the application of heat
...

gi

ca

Uses
...
Araldite which is available in the market comes under this class of resin
...
They set under the effect of atmospheric moisture, resistant to temperature, fungi, insects and chemicals
...
For bonding of silicate containing materials, plastics, rubbers, metals etc
...
Thermoplastic synthetic resins:

te

ch

(a) Cellulose derivatives
...
Cellulose nitrate mixed with alcohol is well known as collodion
...
It is inflammable and in recent years it is replaced by others
...
As multipurpose adhesive, shoe adhesive
...
Cellulose acetate has less adhesive strength than
cellulose nitrate but it is more resistant to heat
...

The film is moisture resistant but inflammable
...
For wall paper paste and also as thickener
...
Polyacrylates are used both in the form of solutions and in the form of
synthetic resin emulsions and are important raw materials for pressure sensitive
adhesives
...
, which are utilized for crosslinking and form better adhesives
...

Uses
...

(c) Polyvinyls
...
Polyvinyl acetate in combination
with phenolic resins forms special adhesives
...
For bonding of glass, metals etc
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH15-1
...
c
ot
og
bl

3
...

y
...
For making conveyer belts
...

ve

rs

it

4
...
The raw materials used for various types of starch and
dextrin based adhesives are potato starch, corn starch etc
...

Uses
...

ca

Uses
...

lu

ni

5
...
These protein glues are obtained from soyabean, corn, casein, albumin
etc
...
They are
very cheap but of poor bond strength
...
Animal glue
...
and hide scraps from
leather industries are degreased with solvent, treated with lime
...
This is bleached and mixed with preservatives
and concentrated to form solid glue
...
The bonding strength of the adhesive is high but susceptible to heat and
moisture
...
For manufacturing cardboard boxes and furnitures
...
Inorganic adhesives
...
forms gel when suspended in water
...
The bond is moisture
and high temperature sensitive but fungus resistant
...
For cardboard boxes making
...

Growth Rates of Different Adhesives
The highest growth rate is expected in automotive industry, transport and electronics
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH15-1
...
c
ot
og

ENGINEERING CHEMISTRY

bl

SHORT QUESTIONS AND ANSWERS

y
...
1
...
Adhesive is defined as a substance capable of joining bodies together by surface
attachments
...
2
...
The theories explaining the mechanism of adhesion are:

(b) Electrostatic theory

(c) Adsorption theory

(d) Diffusion theory

ve

(a) Mechanical theory

ni

3
...
(i) Urea-formaldehyde and phenol-formaldehyde resins are used for joining wooden
surfaces
...
are used for joining glass and cloth
...

EXERCISES

te

ch

no

(iv) Cellulose ethers, esters and also acrylics are used for binding paper
...

What are adhesives?

2
...

3
...

4
...

5
...

6
...

7
...

(a) Polar character

(b) Degree of polymerization

(c) Complexity of molecule

(d) All these

(ii) Adhesive used for bonding metals is
(a) Epoxy resin

(b) Polyesters

(c) Acrylics

(d) All these

(iii) Adhesive used for bonding leather for shoes
(a) Phenol formaldehyde resin

(b) Acrylics

(c) Polyvinyls

(d) Polyesters

(iv) Adhesives used for manufacturing furnitures of wood
(a) Urea-formaldehyde resin

(b) Polyesters

(c) Silicon resins

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH15-1
...
c
ot
og

(v) Natural adhesive used for stamps and envelops etc
...

(a) Araldite
(vi) Adhesive used in aircraft industry is

(b) Asphalt

(c) Shellac

(d) Araldite

it

(a) Starch

rs

(vii) Araldite is

(b) Cellulose derivative

(c) Thermosetting resin

(d) Polyester

ni

Which of the following is fungus resistant?

ve

(a) Animal glue
8
...

Adhesive bonding can be utilized to make a material

(b) Heat insulating

ca

(a) Leak proof

(d) All these

gi

(c) Electrically insulating

10
...
blogspot
...
PM5

337

sp

337

ADHESIVES

...

16

ve

rs

Explosives and Propellants

ni

Explosives

gi

ca

lu

Explosives are pure substances or mixtures which on being subjected to specific stimulus like
mechanical impact, frictional forces, electrical discharge and other sources of heat, high pressure
shock waves initiate an oxidation reaction producing large volume of hot gases
...
The minimum quantity of energy required for initiation has a characteristic
value that depends on the chemical and physical properties of the material
...
The products at hot and high pressure and
when confined to a closed space lead to explosion but if the reaction is controlled at slower rate,
this energy can be utilized to propel a projectile
...

Characteristics of Explosives

te

ch

Following are the characteristics required for an explosive
...
The decomposition rate of an explosive should be very fast and large volume of hot
gases should be liberated exothermally leading to large increase in volume
...
The explosive molecule should have a low energy of dissociation
...
The oxygen-balance of an explosive molecule should be higher which indicates that
more oxygen is available in the molecule to oxidize C and H to CO2 and H2O
...
The explosive should be sensitive towards specific impacts
...
The lesser the stimulus required better
is the sensitivity of the explosion
...
Explosives should not be volatile or hygroscopic but should be stable chemically so
that they do not decompose on keeping or react with the storage container
...
Lastly, explosives should be cheap
...
In coal mines, only very safe
explosives with lowest possible detonation temperature are used
...
In industry explosives are used for blasting ores
of different metals, quarrying limestone to be used in road construction, for blasting holes in
mountains for tunnels and roads, digging earth, seismic prospecting, blasting rocks and other
social and useful works
...
Another area is
in the launching of rockets, spacecrafts etc
...
blogspot
...
c
ot
og

Classification of Explosives

bl

Explosives are classified under three broad groups, namely primary, low and high
explosives
...

(A) Primary explosives
...
They should be handled with great care
...
Only few compounds can act as primary explosives for military and
industrial requirements, they are dense, metallo-organic compounds
...
Mercury fulminate
...
It
is prepared by mixing of solution of one part of mercury with eleven parts of 57% nitric acid
and poured into ten parts of 95% ethyl alcohol when mercury fulminate forms as fine crystals
of 99% purity
...
It decomposes
when stored at elevated temperature, reacts with metals in presence of water
...

gi

ca

2
...
The azides are among the very few useful explosive compounds that do
not contain oxygen
...

Lead azide is made in small batches buffered by the reaction solutions of lead nitrate or
acetate with highly toxic sodium azide
...
Lead azide is less sensitive to ignition than mercury fulminate
...
Lead azide tends to hydrolyse at high
humidity and forms hydrazoic acid, which reacts with Cu and its alloys to produce very sensitive
cupric azide
...
Lead styphnate
...
It is stable and non-corrosive
...

4
...
It is an orange-yellow compound and prepared from picramic
acid [NH2(NO2)C6H2OH], with sodium nitrite and HCl
...
It is non-hygroscopic and sensitive to friction and impact
...

5
...
It is pale-yellow crystalline compound
...
The compound is stable
upto 75°C
...

(B) Low explosives or propellants
...
The burning proceeds from the surface
inwards at a slow rate
...
Typical examples are:
1
...
It is a mixture of 74% potassium nitrate, 15
...
4% sulphur
...
It deteriorates at humidity
...
The hygroscopicity of it is
due to the presence of carbon and impurities in KNO3
...
The decomposition reaction is
10KNO3 + 3S + 8C → 2K2SO4 + 2K2CO3 + 6CO2 ↑ + 5N2 ↑

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH16-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

340

bl

This excess carbon and sulphur undergo slower reduction leading to more gaseous
products

y
...
It is used
for blasting of coal
...

2
...
When
nitration is complete, the nitrocellulose and the spent acid are centrifuged
...
The nitrocellulose so formed is
dissolved in alcohol and ether and the solvent evaporated when it forms a jelly-like mass
...

This product is stored as pressed cylindrical rods
...
So, it is known as smokeless powder
...

1
...
Consist of only one chemical compound such as:

ht
tp
:/
/k
er
al
a

te

ch

no

lo

(i) Ammonium nitrate: It is a powerful explosive compound when once initiated by an
external detonation impulse of sufficient magnitude and in sufficient amount
...
It is readily prepared
by the neutralisation of HNO3 with NH 3, two universally available cheap raw
materials
...
It is also used as an explosive salt
to replace a portion of the nitroglycerine used previously
...

(ii) Picric acid: Chemically picric acid is trinitrophenol
...
It is largely replaced by TNT, because of its objectionable
character as it reacts with metals to form picrates which are dangerously sensitive
...

CH2OH
CH2OH
C
CH2OH
CH2OH

+ 4HNO3 ¾¾®

CH2ONO2
CH2ONO2
C
CH2ONO2
CH2ONO2

+ 4H2O

This explosive compound has become important since the First World War as powerful military explosive
...

The raw material toluene is derived from coal tar or synthetically from petroleum
products
...

Because of its low melting point (80
...
Its
comparative excellence has made it useful for military consumption, in the aspects
like (a) being safe explosive for manufacture, storage and transportation, (b) nonhygroscopic, (c) violent-disruptive explosive, and (d) non-reactive towards metals to
form unstable compounds
...
blogspot
...
PM5

340

...

bl

(v) Cyclotrimethylene trinitroamine RDX or cylonite : This highly powerful explosive
has become important for military use as well as industrial use since World War II
...

(vi) Tetryl or tetranitromethylaniline
...
Tetryl has important use as commercial explosive as a base
charge for blasting caps
...

2
...
These are mixtures of TNT with other explosives
...
Binary explosives are made by mixing,
heating to liquify and pouring into containers to solidify
...
It is an explosive mixture of TNT with ammonium nitrate
...
The detonation products can undergo
further combustion
...
The disadvantage compared to TNT is its hygroscopicity
...

(ii) Tetrytol
...

(iii) Pentolite
...

(iv) Tropex
...

(v) Titronal
...

All these mixtures have some advantages over TNT alone by having higher energy or by
being cheaper
...
Plastic explosives
...

The combination includes a high explosive mixed with wax oil (that gives the plastic nature)
and lower sensitivity
...
They are used for both
industrial and military applications
...
Dynamites
...
Nitroglycerine is an oily liquid, which
detonates by shock or pressure above 50°C
...
In this way, he converted a liquid, which is dangerous to handle and transport, to a
solid which is relatively insensitive to ordinary shock but capable of detonating by a blasting
cap
...

4C3H5 (NO3)3 → 10H2O↑ + 6H2↑ + 12CO2↑ + O2↑
1 vol
...
of explosion

The various types of dynamites are:
(i) Straight dynamites
...
Sodium nitrate is added as an
oxidising agent that adds on good fume properties and good blasting execution
...
Important uses of this class are blasting of hard rocks, coal, minerals etc
...
Gelatin dynamites are made by partly gelatinising the nitroglycerine
by nitrocotton
...
blogspot
...
PM5

341

...

bl

belonging to this class
...
91
...
5% CaCO3
...
Lower ratio of nitrocotton
in nitroglycerin gives viscous liquid instead of the solid mass
...
They are not sensitive to shock
and hence are preferred for use under wet conditions
...
Disadvantage is that they are costly compared to others
...
It is prepared by steeping cotton for 30 minutes in a
cooled mixture of conc
...
HNO3
C6H7O2(OH)3 + 3HNO3 → C6H7O2(NO3)3 + 3H2O

ca

lu

Dry gun cotton can be ignited by shock
...
Dry
gun cotton is used in torpedos, submarines, as a propellant in rifles, artillery shells
...

lo

gi

(iv) Ammonia dynamites
...
Their strengths are equivalent to straight
dynamite but of lower velocity
...
These are
effectiveness, cheapness, insensitiveness to shock and friction, non-inflammability
...

ht
tp
:/
/k
er
al
a

te

(v) Cordite
...
This paste is rolled and cut into pieces of different sizes Vaseline
acts as a stabilizer and cooling agent on the powder
...
Gun cotton controls the explosive reaction of
nitroglycerine and it can be safely used for large caliber naval guns
...
This powerful explosive is a mixture of 65% blasting gelatine and 35%
absorbing powder
...

Permissible dynamites
...
where inflammable gases are present
...

The gelatinous type of permissible dynamites contains a higher percentage of
nitroglycerine and lower content of ammonium nitrate along with a small percentage of
nitrocotton
...

Commercial High Explosives Containing No Nitroglycerine
(i) Ammonium nitrate explosives
...
It is incapable of detonating under the influence of blasting
cap but once initiated by booster charge it can propagate explosion indefinitely
...
blogspot
...
PM5

342

...

bl

by enclosing the material in a waterproof metallic container
...

(ii) Chlorate explosive
...
, becomes highly inflammable and sensitive to impact
...
But though being cheap, they are not popular
...
Carbonaceous absorbent materials like lampblack or
other carbon black are packed in a porous container and this cartridge is dipped into
liquid oxygen to get saturated
...
They are highly sensitive to shock
...

lu

Manufacture of Important Explosives

ht
tp
:/
/k
er
al
a

te

ch

no

lo

gi

ca

(i) Nitroglycerine: The raw materials are 99% pure glycerine, HNO3 and H2SO4
...
In a steel nitrating
vessel, which is cooled externally by brine, the mixed acid is taken and nitroglycerine
is added and nitration is done at a very low temperature under stirring
...
After about 3/4 of an hour, they form separate
layers, nitroglycerine being on the top
...

The yield is around 230, calculated on the basis of glycerine as 100
...
It is very important that to
avoid any accidental explosion a close control of the temperature is to be done during
nitration
...

CH 2 − ONO 2
CH 2OH


Conc
...
Either a two or a three-step process is
used, the former separating out the mono-nitro compound first, then preparing bi
and tri compounds in one step
...

+ 3H2O

H2SO4

NO2

Six isomers are possible for the trinitro compound
...
The liquid
product containing TNT is taken out, washed with ammoniacal solution of Na2SO3
and finally with cold water
...
8°C, which is finally dried and stored
...
blogspot
...
PM5

343

...

NO2

bl

(iii) RDX: Bechman process: (80% yield)

it

CH2—N—CH2
Hexamine + HNO3(98%) + NH4NO3 + (CH3CO)2O → O2N—N

N—N2O

ve

rs

CH2—N—CH2
NO2

ni

Fuses
Fuses are of two types:

gi

ca

lu

(a) Safety fuse: Safety fuse is employed where electrical firing is not used
...
It has an
approximate burning speed of 30 or 40 sec per ft
...

ch

no

lo

(b) Detonating fuse
...
It consists of a charge of high velocity explosive like TNT in a small diameter lead tube
...
A recent type of detonating fuse contains
pentaerythritol tetranitrate in a non-metallic wrapping and the velocity is as high as 7000
metres per sec
...

Squibs

ht
tp
:/
/k
er
al
a

te

When deflagrating explosives like black powder are used, application of flame is
insufficient for firing
...
Squibs may be in metal or cardboard
tubes and may be open or closed at the firing end
...

Blasting Caps

Blasting caps are small cylindrical shells of copper or aluminium containing a detonating
charge of explosives
...

There are three types of blasting caps as shown in Fig
...
1
...

The end of the fuse which is away from the cap is lighted and the spit of flame from the fuse in
the cap fires the ignition charge leading to detonation
...
On passing electric current this bridge wire is heated and becomes
incandescent and fires the ignition charge
...

This time interval can be varied from 15 to 20 sec
...
The composition
of the delays has been improved so that no gas is given off on combustion
...
blogspot
...
PM5

344

sp

344

...

Sulphur seal
Waterproofing
Insulated wire

Sulphur seal

Bridge
wire

Ignition
powder

Capsule

Delay
powder

Base charge

ca

Base
charge

Regular electric
blasting cap

Fuse

lu

Delay
tube

Ignition
powder

Bridge
wire

ni

Waterproofing

Plug

Shell

ve

Air
chamber

gi

Delay electric
blasting cap

Crimp

rs

Shell

Ignition
powder

it

Shell

Plug

Primary
charge
Base
charge

Ordinary
blasting cap

lo

Fig
...
1 Three types of blasting caps
...

(i) Explosives should be treated with care
...

(iii) They should be stored under favourable conditions and at positions sufficiently isolated
from any working furnace or kiln
...

(v) Smoking/fire should be strictly prohibited within 50-m radius from explosive store
...

(vii) All electrical fitting of the store should be properly insulated and only torch light
allowed inside in case of power failure
...

(ix) Nitroglycerine explosives should not be handled in unwrapped condition as it causes
headache etc
...

(x) Contact or inhalation of vapors of aromatic nitrocompounds should be avoided due to
their inherent toxicity
...

(xii) Magazines should be at safe distance from buildings, rail roads and highways
...
blogspot
...
PM5

345

sp

345

EXPLOSIVES AND PROPELLANTS

...

bl

form a large volume of gas
...
The fuel burn and the large vol
...
The generated gases can also be used to drive pumps, empty tanks,
actuate valves, inflate air bags etc
...

ve

(A) Solid propellants
...

lu

ni

1
...
It is a type of homogeneous solid propellant consisting of
mainly plasticized nitrocellulose
...
They can be used only as gun propellants or in
bulk powder fillings for gas generators
...
General composition is 5055% nitrocellulose and 4045%
nitroglycerine, 5% diethyl pthalate as plasticizer giving a smooth mass, 1%
diphenylamine is also added as stabilizer
...

ch

Other compositions are 65% nitrocellulose, 30% nitroglycerine, 5% petroleum jelly, where
the last one functions as plasticizer
...
Nitroguanidine, having a low flame temperature is used as
cold powders for triple-base propellants to reduce the flame temperature
...
They are used as
gun propellants and rocket propellants
...

2
...
Heterogeneously formulated solid propellants that consist of
a polymeric binder in which crystalline oxidizers are incorporated in amounts upto about 90%
by weight
...
Propellants for larger
gas generators are generally of the composite type
...
Composite type have low binder content and the crystalline fillers on
burning produces lager amount of gases and also the flame temperature is comparatively low
...
It gives of a flame temperature of 800-1500°C
and the volume of gases is 400 times the volume of the original
...
The oxidizers are selected which should be stable, non-hygroscopic and
should not produce any corrosive or objectionable product on combustion, viz; ammonium
perchlorate produces HCl on combustion which is corrosive, Aluminium powder in rocket propellant produces large amount of smoke due to Al2O3 formation
...

Energetic substances (RDX or HMX), explosive plasticizers (nitroglycerine etc
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH16-1
...
c
ot
og

sp

347

EXPLOSIVES AND PROPELLANTS

it

y
...
Liquid propellants contain the fuel and oxidizer as a single
substance or mixture of substances (mono) or in two separate phases (bipropellants)
...

Solid propellants are located in a chamber for combustion but the liquid propellants are injected
into the combustion chamber from a storage tank by metering device and hence the engines
using liquid propellants are more delicate
...
Monopropellant has fuel and oxidizer as the same compound or
a solution containing both
...
Monopropellant
for guns have compositions like 63
...
8% water; mixtures of nitromethane and
isopropyl nitrate or methanol
...
But unfortunately H2O2 is highly reactive and decomposition
occurs though stabilizers are added
...

lo

gi

(ii) Bipropellants
...
Commonly used oxidizers are ozone,
liquid O2, liquid fluorine or a mixture of fluorine and oxygen (FLOX)
...

ch

no

Conventional rocket propellants contain H2O2, conc
...
Liquid fluorine
or FLOX is used in aerospace application with improved performance
...
Ozone and liquid fluorine, though
powerful oxidizers, are toxic and explode at high concentration
...

Production

Propellants are energetic materials and hence are to be manufactured and transported
with great care
...
The production processes are:
(a) Solvent process
(b) Solventless processRole and extrusion process
(c) Screw extrusion process
(d) Ball powder process
(e) Casting process
Testing for propellant includes

(a) Burning behaviour (Ballistic Bomb)
(b) Burning rate (Crawford Bomb)
(c) Heat of explosion

The environmentally-safe disposal and toxicological effects of propellants are also of
concern and are coming under strict regulations
...
blogspot
...
PM5

347

...

Explosive: Explosives are pure substances or mixture, which when subjected to
specific stimulus initiate an oxidation reaction producing large volume of hot gases
...

ve

rs

High explosives: High explosives have higher energy content compared to primary
explosives but they are quite insensitive to external stimuli
...

lu

ni

Fuses: Fuse is a thin water-proof canvas length of tube which contains gun-powder
that burn at a given speed for setting off charges of explosives
...

gi

ca

RDX: Powerful explosive consisting of cyclotrimethylene trinitroamine
...
1
...
Explosives are substances or mixtures, which when subjected to mechanical or
thermal shock, lead to rapid oxidation exothermally to produce large amount of gaseous products
of greatly increased volume and also a large amount of energy
...
2
...
Rocket propellant is either a high oxygen containing fuel or a fuel with an oxidant
which is burnt under controlled condition with the evolution of a large volume of gas
...
3
...
Dynamites are high explosives containing nitroglycerine as the principal ingredient
...
with varying amount of nitroglycerine that determines its relative strength
...
4
...
Fuses are thin water-proof canvas length of tube containing gun-powder or TNT,
which burn at a given speed for setting-off the charges of explosive
...

Q
...
What do you mean by oxygen-balance of an explosive?

Ans
...
It
indicates the oxygen contained in the molecule, which will be utilized to oxidize the C and H of
the molecule to form CO2 and H2O, respectively
...

EXERCISES
1
...

sp

348

What are explosives? What are rocket propellants?
How are explosives classified?

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH16-1
...
c
ot
og

bl

y
...

lu

4
...

6
...

8
...

10
...

What are dynamites? State the procedure of its manufacture
...

sp

349

EXPLOSIVES AND PROPELLANTS

no

(a) High energy of oxidation
(c) Positive oxygen balance
(iv) Example of high explosive is

(b) Slow and controlled oxidation rate
(d) Decomposition rate should be slow

te

ch

(a) TNT
(b) Gun powder
(v) Example of primary explosive is

ht
tp
:/
/k
er
al
a

(a) Ammonium nitrate
(vi) Gum powder is
(a) Primary explosive
(c) High explosive

(b) TNT

(c) Lead azide
(c) Lead azide

(b) Low explosive

(vii) Smokeless powder is
(a) Tetracene

(b) Nitrocellulose

(c) Picric acid

(viii) Binary explosives are mixtures of other explosives with
(a) TNT

(b) Dynamite

(c) Nitrocellulose

(ix) Burning speed of safety fuse is
(a) 1 m sec1

(b) 1 cm sec1

(c) 100 m sec1

(b) Mercury fulminate

(c) Gun powder

(x) Black powder is
(a) Nitrocellulose

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH16-1
...
c
ot
sp
og
bl

it

y
...
e
...
e
...
Water is not only essential for the survival of
life, but it is also used for the operation in a large number of industries as coolant, solvent, for
steam generation, for air conditioning, fire-fighting etc
...

Sources of Water

gi

1
...
It is the purest form of natural water
...
and other solids, which pollute the atmosphere
...
Sea water
...
5% dissolved salts
of which about 2
...
Other salts present include sulfates, bicarbonates,
bromides of sodium, potassium, magnesium etc
...

ht
tp
:/
/k
er
al
a

te

ch

3
...
The sources of river water are the springs and the rainwater
...
The
dissolved matters include the salts like sulfates, bicarbonates and bromides of sodium, potassium
and magnesium
...
Lake water
...

5
...
The rainwater and other surface water percolate down through
the soil and rocks and get filtered and finally collected on rocky surface or again come out as
spring
...

Thus we can say that the surface water collects lots of suspended materials, microorganisms and other pollutants from the habitats and become unsuitable for direct human
consumption and other usage
...
Sodium chloride, gypsum (CaSO4
...

(b) Hydration
...

CaSO4 + 2H2O → CaSO4
...
blogspot
...
PM5

350

...
xH2O
Serpentine

bl

Olivine

y
...
Dissolved oxygen brings about oxidation alongwith hydration
...
2H2O
Haematite

Limonite

it

Magnetite

(Soluble)

ve

CaCO3 + CO2 + H2O → Ca(HCO3)2

rs

(d) Action of carbon dioxide
...

(Insoluble)

ni

K2O
...
6SiO2 + CO2 + 2H2O → Al2O3
...
2H2O + K2CO3 + 4SiO2

Hardness of Water

lo

gi

ca

lu

Hardness of water is the characteristic of preventing lather formation of water with
soap
...
This hard water on treatment with soap which is stearic or palmitic acid salts of
sodium or potassium causes white precipitate formation of calcium or magnesium stearate or
palmitate
...
When the hardness causing ions are removed as insoluble soaps, water becomes soft
and forms lather
...

Fe2+
...
Permanent hardness cannot be removed easily on boiling
...
The choice
of CaCO3 is due to the fact that its mol
...
is 100 and equivalent weight is 50 and it is the most
insoluble salt in water
...
Other limits include French degree of
hardness, English degree of hardness or Clark, USA degree of hardness and German degree of
hardness
...
blogspot
...
PM5

351

sp

351

WATER TREATMENT

...
83 × 10 4

1 German degree of hardness =

y
...
6 × 10 4

ni

Relation between various units of hardness
1 ppm
= 1 mg/l
= 0
...
degree of hardness =

og

ENGINEERING CHEMISTRY

= 0
...
43° Fr

= 0
...
3 ppm

= 0
...
3 mg/l

1° Fr

= 10 ppm

= 10 mg/l

= 0
...

ca

lu

1 mg/l
1° Cl

te

ch

no

lo

gi

Disadvantages of Hard Water
(a) In domestic uses
...
It also creates sticky precipitates that deposit on bath
tub, body, clothes etc
...
Thus a lot of soap get wasted
also
...
Due to the presence of hardness producing salts in hard water, boiling point gets
elevated and during cooking a lot of fuel is wasted
...
do not cook in hard water
...
Drinking of hard water is also problematic since it affects
the digestive system and at the same time the possibility of deposition of calcium oxalate
crystals in the urinary tract is alarming
...
For textile industry and dyeing industry, hard water causes the
usual problem of deposition of insoluble salts that interfere with the proper dyeing and printing
of the fabrics
...
Hard water also hampers
the economy by wastage of soap as it does not form good lather
...

• Calcium and magnesium salts also interfere with the smooth and glossy finish of the
papers in the paper industry
...

• In laundry, hard water causes wastage of costly soap and also interferes with the
coloration due to the staining of iron salts
...

• Hard water is not suitable for preparing drug solutions in pharmaceutical industry
...

Sludge and Scale Formation in Boilers
When hard water is used for boilers, on continuous evaporation, the salts present in the
hard water gets saturated and are finally deposited in the areas where the flow is slow
...
blogspot
...
PM5

352

sp

352

...

bl

these precipitates are loose and slimy in nature, it is called sludge whereas when these
precipitates are hard and they adhere strongly to the inner surface of the boilers, they are
called scale
...
Sludge is formed by the presence
of MgCO3, MgSO4, MgCl2, CaCl2 etc
...

Disadvantages of sludge formation are (i) poor heat conduction due to the presence of
sludge on the surface; (ii) difficulty in the operation of the boiler; (iii) if sludge is formed along
with the scale and is trapped within the scale formed and so it is difficult to remove and (iv) it
clogs the pipe lines and other connections to the vessel near the places where water circulation
rate is slow
...
Sludge formation can be prevented by (i) using soft water for boiler
operation and (ii) removing the concentrated salty water from time to time so that deposition
of sludge is prevented
...
This scale formation takes place due to the following reasons:
(a) In low pressure boilers scale formation occurs due to the formation of CaCO3 from
Ca(HCO3)2
...
e
...
But here
CaSO4 forms the hard scale
...

Similar hard scales are formed when SiO2 is present in the hard water
...
These calcium or magnesium silicate scales are very difficult to remove
...

Disadvantages of scale formation are similar to sludge formation but the severity is
more, since its removal is more difficult
...
The
increase in thickness of the scale from 1
...

(ii) Due to the overheating of the boiler, different parts of the boiler become weak and
distorted and so the operation of the boiler becomes unsafe, particularly the high
pressure boilers
...

(iii) Valves and condensers of the boilers are chocked due to scale formation and boiler
efficiency decreases
...

(ii) Blow down operations for loose scales
...

(iii) Giving thermal shocks, which involve alternate heating and cooling to make the
scales brittle
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH17-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

354

bl

These are methods for the removal of the scales, when they are formed
...

ht
tp
:/
/k
er
al
a

te

ch

no

lo

gi

ca

lu

ni

ve

rs

it

y
...
Important internal
treatments involve
...

(b) Different sodium phosphates like NaH2PO4, Na2HPO4 and Na3PO4 are added to high
pressure boilers to react with the hardness forming impurities to form soft sludge of
calcium and magnesium phosphates and finally this can be removed by blow down
operation
...

CaSO4 + Na2CO3 = CaCO3 + Na2SO4
...
e
...

2CaSO4 + [Na4P6O8]2 → [Ca2P6O18]2 + 2Na2SO4
(e) Sodium aluminate conditioning: Sodium aluminate is hydrolysed yielding NaOH
and gelatinous Al(OH)3
...
This Mg(OH)2 and Al(OH)3 are flocculent and entraps the colloidal as
well as the finely divided impurities like silica in the boiler water and the loose
precipitate is finally removed by blow down operation
...

( g) Radioactive conditioning: Tablets of radioactive salts placed inside a boiler emit
radiations, which prevent scale formation
...
In steam boiler
operation, the chemicals that are believed to be responsible are NaOH and silica
...

Na2CO3 + H2O → 2NaOH + CO2
Steam boilers are made by rivetting constructions rather than welding and are
particularly liable to damage by caustic alkali solutions
...
NaOH
attacks and dissolves out iron of boiler forming sodium ferroate
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH17-1
...
c
ot
og

Dilute
NaOH
Solution

Fe at
plane
Surfaces

y
...

lu

ni

ve

rs

it

Prevention of Caustic Embrittlement
(i) Addition of sodium phosphate as softening agent instead of Na2CO3
...
5, whereby
the deposition of Na2SO4 prevents the penetration of NaOH into the cracks and stops
caustic embrittlement in high pressure boilers
...
also prevents cracking
similar to sodium sulfate in low pressure boilers
...

Corrosion in Boilers

no

lo

gi

ca

Boiler corrosion occurs by chemical or electrochemical attack of the contents of water
...
Greater the pressure, higher the dissolved O2
content
...

2Fe + 2H2O + O2 → 2Fe(OH)2 ↓
4Fe(OH)2 ↓ + O2 → 2[Fe2O3
...
01 ppm
...

(iii) Ion exchange techniques also reduce oxygen concentration to very low level
...
This CO2 dissolves in water forming carbonic acid
which causes local corrosion called pitting
...

(ii) Adding lime or NH3
...

(c) Mineral acids: Water from industrial areas contains acidic wastes or inorganic salts
which on hydrolysis produce acids
...
The acids react with
iron in chain reactions producing acids again and again and also produce H2 causing hydrogen
embrittlement which leads to boiler failure
...
blogspot
...
PM5

355

sp

355

WATER TREATMENT

...

bl

During rapid steam production, some liquid water drops are also carried along with the
steam
...

Priming occurs due to (i) presence of large amount of dissolved solids, (ii) high steam
velocities, (iii) sudden boiling and (iv) sudden increase in steam production
...

Foaming is the production of bubbles and foams which do not break easily
...

Foaming can be reduced by (i) removing oil from boiler-feed water and (ii) adding antifoaming agents
...
Actual height of the water column
cannot be judged due to foaming hence creating difficulty in the maintenance
...

• Impurities present in water:
(i) Suspended, (ii) Colloidal, (iii) Dissolved impurities
• Temporary hardness is due to Ca(HCO3)2 and Mg(HCO3)2 and can be removed by
boiling
...

• Hardness expressed in equivalent amount of CaCO3
Mass of hardness producing substances × 50
=
Chemical equivalent of hardness producing substances
• 1 ppm hardness ≡ 1 part of CaCO3 equivalent hardness in 106 parts of water
...

Softening of Water

Softening of water means the removal of calcium, magnesium, iron salts and similar
other metallic ions, which would form insoluble metallic soaps
...
Cold and hot lime-soda process
...
Permutit or zeolite process
...
Ion-exchange or demineralization process
...
Lime-soda process
...
The insoluble
precipitates of CaCO3 and Mg(OH)2 are removed by filtration
...

For the removal of temporary hardness the reactions are:
Ca(HCO3)2 + Ca(OH)2 → 2CaCO3 ↓ + 2H2O
Mg(HCO3)2 + Ca(OH)2 → 2CaCO3 ↓ + MgCO3 + 2H2O
MgCO3 + Ca(OH)2 → Mg(OH)2 ↓ + CaCO3 ↓
Hence, to remove equivalent quantities of Ca and Mg hardnesses the amount of lime
necessary is in the ratio of 1:2
...
blogspot
...
PM5

sp

356

356

...

bl

Again for the removal of permanent hardness
...
Extra addition of Ca(OH)2 causes hardness
...

ni

ve

In the actual process the water is thoroughly mixed with the chemicals and allowed to
react for sufficient time
...
are added as
coagulants
...

Cold Lime-Soda Process

no

lo

gi

ca

lu

In this method, calculated quantity of chemicals and water, along with accelerators and
coagulators are added to a tank fitted with a stirrer (Fig
...
1)
...
After softening the soft water rises upwards and the heavy sludges settle
down
...
Cold lime soda process is used
for partial softening of municipal water, for softening of cooling water etc
...

Driving belt

Motor

ch

Chemicals
(soda + lime
+ coagulant)
feed inlet

ht
tp
:/
/k
er
al
a

te

Raw water
feed inlet
Filtered softened
water outlet

Wood-fibre
filter

Outer chamber
Stirrer
paddles

Inner chamber

Stirrer

Sedimented
sludge
[CaCO3, Mg(OH)2]

Sludge outlet

Fig
...
1 Continuous cold lime-soda softener
...
blogspot
...
PM5

357

...

bl

This process is similar to the cold lime-soda process
...
As the reaction takes
place at high temperature, there are the following advantages:
the precipitation reaction becomes almost complete
...

the sludge settles rapidly
...

dissolved gases (which may cause corrosion) are removed
...

Residual hardness is low compared to the cold process
...

(b) Ionical sedimentation vessel where the sludge settles down and
(c) Sand filter where sludge is completely removed
...
17
...

Advantages Include:
(i) Lime soda process is economical
...

(iii) Mineral content of the water is reduced
...

ch

no

lo

gi

ca

lu

ni

ve

rs

it

(i)
(ii)
(iii)
(iv)
(v)
(vi)
(vii)

Raw water
feed inlet

te

Super
heated
steam inlet

ht
tp
:/
/k
er
al
a

Chemicals
(lime + soda)
feed inlet

Reaction
tank

Softened
water
Fine
sand
layer

Conical
sedimentation
tank

Coarse
sand layer

Sand
filter
Gravels layer

Precipitated
sludge
[CaCO3, Mg(OH)2]

Precipitated
sludge outlet

Filtered
softened
water outlet

Fig
...
2 Continuous hot lime-soda softener
...

(ii) Due to residual hardness, water is not suitable for high pressure boiler
...
blogspot
...
PM5

sp

358

358

...

bl

Zeolite is hydrated sodium alumino silicate capable of exchanging reversibly its sodium
ions for Ca2+ and Mg2+, having the general formula Na2O
...
xSiO2
...
Common zeolite
is Na2O Al2O3
...
2H2O and is known as natrolith
...
are
used for water softening
...
These are porous and glassy
and have greater softening capacity than green sand
...

Method of Softening: Hardwater is passed through a bed of zeolite at a specific rate at
ordinary temperature; the hardness causing cations i
...
, Ca2+ and Mg2+ are exchanged for Na
and it is converted to CaZe and MgZe
...

ch

no

CaZe or MgZe + 2NaCl = Na2Ze + CaCl2 (Or MgCl2)
The washings containing CaCl2 or MgCl2 are wasted
...

ht
tp
:/
/k
er
al
a

te

Hard water in

Top distributor

Injector

Zeolite sand

Soft water
out

Gravel

Salt storage
Waste

Fig
...
3 Softening of hard water by permutit process
...
(i) Hardness of water can be removed completely upto about 10 ppm; (ii) The
equipment used is small and easy to handle; (iii) It requires less time for softening; (iv) There
is no sludge formation, hence the process is clean; (v) Easy to regenerate; (vi) Any hardness
can be removed without any adjustment of the process
...
(i) Coloured water or water containing suspended impurities cannot be
used before filtration; (ii) Water containing acid cannot be used for softening since acid may

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH17-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

360

bl

destroy the zeolite; (iii) Since on removal of Ca2+ and Mg2+ the soft water contains large amount
of NaHCO3, this on heating liberates CO2, which causes corrosion in the boilers and hence this
soft water is not suitable for boilers
...

Ion Exchange or Demineralization

ni

ve

rs

it

Ion exchange resins are organic polymers which are crosslinked having microporous
structure and the functional groups are attached to the chains which are responsible for the
ion exchange properties
...
e
...

ca

lu

¾CH¾CH2¾¾CH¾CH2¾
SO3H
SO3H

n

cation exchange resin

no

lo

gi

(ii) Anion exchange resins (ROH): The styrene divinyl benzene or amine formaldehyde
copolymers contain quaternary ammonium tertiary sulphonium or amino group in
the resin
...
e
...

te

ch

CH2¾CH¾¾CH2¾¾CH¾¾CH2¾¾CH¾CH2

–

ht
tp
:/
/k
er
al
a

CH2NMe+OH
2

CH2NMe+ OH
2
CH2¾CH¾CH2¾CH----CH2

–

----CH2----CH

CH2NMe+ OH
2

–

CH2NMe+ OH
2

–

Anion exchange resin

Method: The hard water is passed first through cation exchange resin similar to the
permutit process whereby the cations like Ca2+, Mg2+ are removed from the hard water and
exchanged with H+ as follows:
2RH+ + Ca2+/Mg2+ → R2Ca2+/R2Mg2+ + 2H+

After this the hard water is again passed through anion exchange column, which
exchanges all the anions like SO42, Cl etc
...
Thus the water coming out finally
from the two exchangers is ion free and called deioinized or demineralized water
...
blogspot
...
PM5

360

...

bl

og

sp

361

WATER TREATMENT

Injector

Waste
Acid
regenerator liquor

ve

Pump

Anion
exchanger
gravel

rs

Cation
exchanger
gravel

it

Injector

ni

Waste
liquor

Alkaline
regenerator

OH
O

te

C
C

C
O
Ca
O

C

ht
tp
:/
/k
er
al
a

Filter bed

C

C

ch

C

HO

no

O

lo

Cation
exchange

C

C

H

O
HO

H

C

C

C

C

C

C

C
ONa+

O

C
Cl

–

––

C–N–H

SO4

H
H

+

H
H

H–N–C

H
SO4 H

C

H–N–C

H–Cl

C

C

––

C–N–H

–

C

H–N–C

H
H

C

C

C

H–N–C

––
H
C
SO4
H
C–N–H

––

C

–

OH

C–N–H

SO4

C

H
HOH

H–OH OH
H

–

C

H

r

H–N–C

–

C
Cl

ate

HO–H

H–OH
H

C

Cl
Cl

H

C–N–H

C

Na O
O
C
++ O
Ca
O

O

C

C

+

C

C
C

O
O
C

O
O

+

C

C
+

H

W

Anion
exchange

C

+

C

C

+

gi

H

D
...

ca

+

H

lu

Fig
...
4 Demineralisation of water
...
17
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH17-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

362

y
...
NaOH

bl

Regeneration: The inactivated or exhausted cation exchange resin is regenerated by
dil
...

it

R2SO42 + 2OH → 2ROH + SO42+
The columns are finally washed with deionized water and the washings are discarded
...
Hence, water while passing through the column comes in
contact with the two exchangers for a large number of times and the hardness is reduced to a
very low level (1 ppm)
...

Advantages of ion exchangers include (i) Easy regeneration; (ii) both acidic and alkaline
water can be softened; (iii) residual hardness is very low and hence the water is suitable for
high pressure boilers also
...
It needs prior filtration
...

It should be devoid of any unpleasant taste
...

It should be devoid of heavy metals and arsenic
...

Content of dissolved salts should not exceed 500 ppm
...

Natural water from river, lakes, canals are treated for the domestic purpose
...

• Settling in a large tank to remove suspended impurities
...
Chemical coagulants are generally (i) Alum [K2SO4, Al2(SO4)3
...
7H2O]
...

• The gelatinous precipitates mainly contain aluminium hydroxide, ferrous and ferric
hydroxides (ferrous hydroxides are converted to ferric hydroxide by the dissolved oxygen
of water)
...

• These partially clarified water is filtered through sand gravity filters
...
blogspot
...
PM5

362

...
5 meter thick and at bottom a gravel of 0
...

it

(i) By addition of bleaching powder (1 kg per 1000 kiloliters)
...

Sterilization

Here sterilization is effected by the HOCl generated by the following reaction:

rs

Ca(OCl)Cl + H2O → Ca(OH)2 + Cl2

ve

Cl2 + H2O → HCl + HOCl
and this HOCl kills the germs
...

ca

(ii) By direct chlorination: Here also the generated HOCl kills the pathogenic bacteria
...
3-0
...

gi

Advantage of using Chlorine
...

no

lo

Disadvantages
...
Dissolved chlorine causes irritation to mucus membrane and lowers the pH of water
below 6
...
The treated water should contain chlorine less than 0
...

ht
tp
:/
/k
er
al
a

te

ch

(ii) Break-point Chlorination
It is seen that when liquid chlorine is added or chlorine gas is passed through water the
consumption of chlorine makes the available chlorine less and after some time the available
chlorine increases
...
Then available chlorine again increases due to
decomposition of chloro-organic compounds
...
The
point at which the residual chlorine begins to appear is known as break point and at this point
water is devoid of bad taste and odours and is bacteria free
...

• Pathogenic bacteria are destroyed completely
...

(iii) Sterilization by Chloramine
When chlorine and ammonia are mixed in the ratio 2:1 of volume chloramine is formed
...
NH2 + HCl
Chloramine is much more effective than chlorine in its bactericidal (bacteria killing)
action
...

Cl
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH17-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

364

bl

The use of chloramine for sterilization is gaining importance as it does not impart any
irritating odour and does not affect the taste of the treated water
...

(iv) Sterilization by Ozonization
Ozone is an unstable gas and decomposes to give nascent oxygen
...
The ozone treatment plant
consists of a tower made of enamelled iron, separated by perforated celluloid partition into a
large number of compartments, ozone is passed through bottom and the water is allowed to
percolate through the celluloid partition
...
This makes the treatment most
effective
...

gi

ca

(b) Ozone does not impart any unpleasant taste or odour to the treated water and does
not change its pH appreciably as it simply decomposes into oxygen
...

lo

(c) Time of contact is only 10-15 minutes and dose strength is only 2-3 ppm
...

ch

no

Sterilization through Physical Methods
(i) Boiling, (ii) Exposure to the sunlight, (iii) Sterilization with UV light
...
Sulphur dioxide is very common as an antichlor
...

Cl2 + H2O = HOCl + HCl

H2O + SO2 = H2SO3

HOCl + H2SO3 = HCl + H2SO4

SO2 + Cl2 + 2H2O = 2HCl + H2SO4
H2O2 + Cl2 = 2HCl + O2↑

Dechlorination is needed to avoid the harmful effects of treated water
...
The process of removal of common salt
from this brackish water is called desalination
...

(a) Electrodialysis
...

From Fig
...
6 we can find that when direct current is passed through saline water, the Na+
ions move towards the cathode while Cl ions move towards the anode through the membrane
and collect in the two side compartments while the central compartment contains pure
desalinated water
...
blogspot
...
PM5

364

...

Anode

bl

Sea water

Sea water

rs

Negative ions

ve

Positive ions

Membrane

Pure
water

lu

Concentrated
brine

ni

Membrane

Concentrated
brine

ca

Fig
...
6 Line diagram of electrodialysis
...
These membranes are selective as they are
made up of materials containing fixed functional groups
...
17
...
Cations and anions pass through the membrane pairs and we obtain alternate
streams of pure water and concentrated salt solution
...
17
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH17-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

366

it

y
...
Osmosis describes the flow of solvent from dilute to concentrated
solution through a semipermeable membrane
...
e
...

Piston

no

Chemical Analysis of Water

lo

gi

ca

lu

ni

ve

rs

The cellulose acetate and the more recently used
polymethacrylate and polyamide membranes do not allow
the solute pass, while the solvent is forced through and
Sea water
Stout semicollected as a pure solvent in a direction as shown in
permeable
membrane
Fig
...
8
...
17
...

economical, as the membrane lifespan is high, (iv) uninterrupted supply of large volume of
water for industrial or domestic purpose can be obtained
...

ht
tp
:/
/k
er
al
a

te

ch

1
...
The residual free chlorine remaining after the municipal
processing of domestic water is injurious to health and hence estimation of this free chlorine is
essential
...

The chlorine present liberates an equivalent amount of iodine which can be estimated with
standard thiosulfate solution using starch as an indicator
...
The end point indicates a change
from deep-blue to just colorless solution
...
5 × 10 6
ppm
...
Alkalinity
...

(a)
OH + H+ → H2O

CO32+ H+ → HCO3

(b)
HCO3 + H+ → H2O + CO2

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH17-1
...
c
ot
og

sp

367

WATER TREATMENT

ni

(V1 + V2 ) × 50 × 106
ppm
...

bl

These estimations are done by (a) titrating against standard acid solution using
phenolphthalein as an indicator and (b) using methyl orange as an indicator
...
The same solution is
further titrated with 2 to 3 drops of methyl orange indicator
...
of acid upto phenolphthalein end point = V1
Extra volume of acid added to get methyl orange end point → V2 ml
...
Hardness

gi

(a) Estimation of temporary hardness
...
Temporary hardness is determined by finding the
alkalinity of water before and after boiling, since temporary hardness is removed on boiling
...
Let the volume of acid be V1
...
Add 100 ml of distilled water to the beaker and
dissolve the residue left
...
Let the volume of acid required be V2 ml
...
The estimation is done by adding
excess of standard Na2CO3 solution to a given volume of boiled water containing permanent
hardness
...
The residual Na2CO3 is titrated
against standard acid and the difference of Na2CO3 equivalent gives permanent hardness
...
50 ml of N/50 Na2CO3 solution
is added and boiled for 15 minutes
...
Let titre vol
...

=

∴ Permanent hardness =

(50 − V) × 10 6
ppm
...
Disodium salt of
ethylene diamine tetra acetic acid (EDTA) is used as a complexing agent for Ca2+, Mg2+
...
blogspot
...
PM5

367

...

bl

Erichrome black T is used as an indicator and pH is maintained at pH 10 using NH4OH/
NH4Cl buffer
...
When EDTA added and the total Ca2+, Mg2+ forms complex with it and the indicator
becomes free, the colour of the solution changes from wine red to blue at the end point
...
5 gm
...

Standard EDTA solution (N/100): 4 gm of EDTA dissolved with 0
...

rs

M
Zinc acetate solution (primary standard) is taken, to it 5 ml of NH4Cl
100
NH4OH buffer and a few drops of EBT indicator are added and titrated to blue end point with
EDTA and the strength of EDTA is calculated
...
Let the volume of titrant be
V ≈ (f) M/100 EDTA solution
...
001 × V × f × 106
ppm
...

Buffer solution: A mixture of 142 ml of conc
...
5 gm NH4Cl is diluted to
250 ml distilled water
...

(ii) Zeolite or permutit process
...

• Micro-organisms from potable water can be removed by:
(i) Boiling for 10 to 15 minutes
(ii) Bleaching powder treatment
(iii) Chlorination with Cl2
(iv) Chloramine treatment
(v) Ozonization
...

• Exhausted ion-exchange resins are regenerated by:
(i) Cation exchangers regenerated by passing strong acid solution through the bed
(ii) Anion exchangers regenerated by passing strong base solution through the bed
...

(ii) Complexometric titration by EDTA
• Units of hardness are:
(i) ppm
(ii) mg/litre (1 ppm = 1 mg/litre)
(iii) Clarks degree (1 ppm = 0
...
1° Fr)
...
)

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH17-1
...
c
• Water is hard if it contains calcium or magnesium ions
...

• Scum is a precipitate formed when soap comes in contact with hard water
containing above mentioned ions
...

• Temporary hardness is removed by boiling
...

lu

boiling

ca

• The solid calcium carbonate is precipitated as scale, which affects heating element
of boilers and gradually blocks the pipes in heating system
...

gi

• The mineral gypsum (CaSO4) is slightly soluble in water and makes water
permanently hard
...

PROBLEMS

ht
tp
:/
/k
er
al
a

te

Problem 1
...
5 mg/l
...
CaSO4 = 13
...
6 × 100 OP mg/l
...
Temporary hardness = 7
...
How many mg
...

(56 + 16 + 64)g of FeSO4 ≡ 100 g CaCO3

For 100 ppm hardness FeSO4 required per 106 parts of water is 136 parts
...

2−
Problem 3
...
6 ppm
...
blogspot
...
PM5

369

sp

ot
bl

• Hard water does not easily lather with soap, instead it forms a greasy scum
...
c
ot
15
...

60

y
...
6 ppm = 15
...

∴

og

ENGINEERING CHEMISTRY

it

= 2
...

Problem 4
...
5 ppm; Mg(HCO3)2 = 12
...
2 ppm; MgSO4 = 2
...
5 ppm
...

ni

Calculate (i) temporary and permanent hardness and (ii) the vol
...
481 ppm CaCO3
162
100
= 8
...
(i) Ca(HCO3)2 = 10
...
5 ×

gi

Mg(HCO3) = 12
...
5 ×

100
= 7
...
6 ppm = 2
...
167 ppm CaCO3
120

no

lo

CaCl2 = 8
...
2 ×

100
= 5
...
481 + 8
...
5 ppm = 7
...
043 ppm
= (7
...
167 + 5
...
069 ppm

∴ Total hardness

= (15
...
069) = 30
...

30
...
11 ml
...
Calculate the amount of lime and soda required for softening 50,000 litres
of hard water containing
∴ Volume of M/100 EDTA required =

MgCO3 = 144 ppm;

CaCO3 = 25 ppm;

MgCl2 = 95 ppm;

CaCl2 = 111 ppm;

Fe2O3 = 25 ppm;

Na2SO4 = 15 ppm
...
MgCO3 = 144 ppm = 144 ×

100
= 171
...

MgCl2 = 95 ppm =
CaCl2 = 111 ppm =

95 × 100
= 100 ppm CaCO3
95
111 × 100
= 100 ppm CaCO3
111

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH17-2
...
c
ot
og

74
[2 × MgCO3 + CaCO3 + MgCl2] × volume of water
100

bl

∴ Lime required =

74
[2 × 171
...
0] × 50,000 mg
100
= 17,309,000 mg = 17
...

Problem 6
...
Calculate the lime (87% pure) and
soda (91% pure) required to soften 1 million litres of water sample
...

rs

it

y
...
65 ppm CaCO3
24
30 × 100
CO2 = 30 ppm =
= 68
...
of water
100

lo

∴ Lime requirement =

150 × 100
= 122
...
65 + 68
...
95] × 106
100
= 218
...
9 kg
...
of water
...
65 − 122
...
6 × 106 mg = 33
...

Problem 7
...
having a strength of 150 g/l of NaCl
...

=

Sol
...
932 × 104 g CaCO3

= 22,500 ×

If the hardness of water is 600 ppm
∴

1
...
129 × 104 litres

Vol
...
10 ml of 0
...
50 ml of a water sample required 20 ml of the above EDTA solution
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH17-2
...
c
ot
FG IJ
H K

L M O EDTA solution ≡ 1 g CaCO
M 100 P
N Q
F M IJ EDTA solution = 1 × 20 × 0
...
ml

∴ 50 ml of the water sample contains 0
...
019 g CaCO3
...
019 × 10 6
= 377
...
85
= 0
...

Sol
...
8 ppm
...
A sample on water on analysis has been found to contain the following :

ca

Ca(HCO3)2 = 10
...
Mg (HCO3)2 = 12
...
5 ppm
CaCl2 = 8
...
6 ppm
...

10
...
481 ppm
162
12
...
5 ppm =
= 8
...
5 × 100
CaSO4 = 7
...
515 ppm
136
8
...
2 ppm =
= 7
...
6 × 100
= 2
...
6 ppm =
120
∴ Temporary hardness = (6
...
562) = 15
...
043 × 0
...
504° Fr
Permanent hardness
= (5
...
387 + 2
...
069 ppm
= 1
...

Ca(HCO3)2 = 10
...

SHORT QUESTIONS AND ANSWERS

Q
...
What is the need for Desalination of water programme?
?
Ans
...
So for drinking,
domestic and irrigation purposes river water and other sweet water sources seem to be
insufficient
...

Q
...
What are the causes of corrosion of boilers?
?
Ans
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH17-2
...
c
ot
og

sp

373

WATER TREATMENT

ni

ve

rs

it

y
...

?
Q
...
What are the disadvantages of scale formation in a boiler?
Ans
...

• Tubes and plates are clogged as a result the efficiency of the boiler is decreased
...

MgCl2 + Fe + H2O = Mg(OH)2 + FeCl2 + H2
Q
...
Why is demineralisation preferred to zeolite softening?
?

ca

lu

Ans
...

?
Q
...
Why is chloramine preferred to Cl2 for sterilization of drinking water?

gi

Ans
...

Q
...
What are the criteria for drinking water?
?

lo

Ans
...

?
Q
...
Why is UV radiation superior to other methods of sterilization of water?

no

Ans
...

ht
tp
:/
/k
er
al
a

te

ch

Q
...
What is pitting?
Ans
...
Dissolved gases like O2, CO2 , H2S corrode the iron
surface of the boiler particularly near the rivet, bends and leads to leak or boiler failure
...
9
...
When the boiler water is difficult to soften or purify, some chemical substances are
added to the boiler water that makes the scale in the boiler loose and easily removable
...

Q
...
What is plumbo solvancy? How can it be prevented?
?
?
Ans
...

2Pb + 2H2O + O2 = 2Pb(OH)2
The hydrolysis of Ca2+ and Mg2+ salts dissolved in water may lead to the formation of
lead salts like PbSO4 and PbCl2
...
This phenomenon is known as plumbo
solvancy
...

Lead poisoning can be prevented by treatment of the water with alkali silicate and
phosphate followed by filtration
...
blogspot
...
PM5

373

...
11
...

rs

Ans
...

Q
...
State the harmful effects of silica present in water
...

bl

Ans
...

Q
...
What is break-point chlorination?
?

ve

Ans
...

Q
...
What is the difference between hard water and soft water?
?

lu

ni

Ans
...
15
...
Why?
CO3
?
3

ca

Ans
...

Q
...
Why do we express hardness of water in terms of CaCO3 equivalent?
?

no

lo

gi

Ans
...
wt
...
Moreover, it has also been adopted as standard
for expressing hardness
...
17
...
Temporary hardness ⇒ Ca(HCO3)2 and Mg(HCO3)2
Permanent hardness ⇒ Chloride and sulphate of Ca2+ and Mg2+
...
18
...
Define them
...
(i) ppm, (ii) degree
...

Degree hardness is defined as the parts of hardness salt present in 105 parts of water
expressed in terms of calcium carbonate
...
19
...
Do you think that water will be hard?
?
+ and Zn2+ both form insoluble soaps
...
Yes, as Li
Q
...
Calculate the hardness of

FG M IJ MgSO
H 1000 K

4

solution
...
MgSO4 = CaCO3
120 g = 100 g

FG M IJ MgSO
H 1000 K

4

solution contains =

120
100
g, MgSO4 =
CaCO3 in 1000 ml water
...
1
× 106 = 100 ppm
...
1
Again, hardness in degree =
× 105 = 10
1000
So, hardness in ppm

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH17-2
...
c
ot
og

sp

375

WATER TREATMENT

Q
...
The presence of carbon dioxide is avoided in boiler feed water
...

bl

Ans
...

y
...
22
...
When hard water comes in contact with soap Ca2+ and Mg2+ ions react with soap
and scum is formed when the reaction is overconsuming much of soap, lather is then formed
...

rs

Q
...
Why is calgon conditioning better than phosphate conditioning?
?
Ans
...
e
...

Q
...
Why is water softened before using in boiler?
?

ca

Ans
...
That is why water is softened before using in boiler
...
25
...
Sodium sulphate when used blocks hair cracks thus prevents infiltration of caustic
soda through the cracks
...

Q
...
State two harmful effects of silica in water
...
Silica reacts with Ca2+ and Mg2+ ions forming calcium silicate and magnesium
silicate in boiler
...

ht
tp
:/
/k
er
al
a

EXERCISES

1
...

2
...

3
...

Distinguish between:

(a) Temporary and permanent hardness
...

(c) Softening and demineralization
...

Write notes on: (i) Caustic embrittlement, (ii) Reverse osmosis, (iii) Priming and foaming,
(iv) Hot lime-soda process, (v) Boiler corrosion
...

What is the principle involved in the determination of total hardness of water by EDTA method?

7
...
Why coagulants
are not used in hot lime-soda process?

8
...

During deionization process, water is first passed through cation exchanger and then through
anion exchanger, why?

10
...
Why is chloramine better than chlorine for sterilization of water?

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH17-2
...
c
ot
og

ENGINEERING CHEMISTRY

7
...

9
...

it

rs

ve

ni

lu

ca

ht
tp
:/
/k
er
al
a

10
...

lo

5
...

ch

3
...

Hard water can be softened by passing through
(a) Calgon
(b) Sodium silicate
(c) Ion exchange resin
...

Pure water can be obtained by
(a) Lime-soda process
(b) Boiling
(c) Demineralization
...

The chemical that gets dissolved in high pressure boilers
(b) CaCO3
(c) CaSO4
...

The most ideal disinfectant in water works is
(a) Chlorine
(b) Bleaching powder
(c) Chloramine
...

Write a short note with a proper sketch diagram on reverse osmosis process for desalination of
brackish water
...

Correlate the various units of the hardness
...

(a) What are scales? What are the ill-effects of scales?
(b) How can scale formation be prevented by (i) Phosphate conditioning and (ii) Calgon conditioning?
Distinguish between:
(a) Purification and softening of water
(b) Boiler scales and sludges
(c) Internal and external treatment of water
...
How can the factors can be eliminated?
Describe the process of water softening by permutit process
...

bl

OBJECTIVE TYPE QUESTIONS
1
...

12
...

14
...

16
...

18
...

20
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH17-2
...
c
ot
og

bl

y
...

29
...

31
...

27
...

Write down the requirements for drinking water
...

What is desalination? Name the different methods involved in desalination? Describe any one in
detail
...

(a) What do you mean by carbonate and non-carbonate hardness of water?
(b) State harmful effects of silica present in water
...

Write different methods of sterilization
...

What are the methods involved for determination of temporary and permanent hardness of water?

ni

22
...

24
...

sp

377

WATER TREATMENT

ca

PROBLEMS

The hardness of 1,00,000 litres of a sample of hard water was completely removed by passing
through a zeolite softener
...
Calculate the hardness of the sample water
...
64
...

A sample of hard water has a hardness of 510 ppm
...

no

lo

gi

1
...
07° Clark = 0
...
35
...
Calculate the hardness in ppm
...

In an experiment for the determination of hardness of a sample of water, the following results
are obtained:

ch

3
...
62
...

FG N IJ Na CO solution is added to it = 20 cc
...

From these data calculate the hardness of water in grains per gallon
...
6
...
4 grain
...

A precipitate of 0
...
H2O) was obtained from a 250 ml of water
sample
...

[Ans
...

Analysis of a sample of water revealed the content of dissolved salts in the following data:
Mg(HCO3)2 = 22 mg l1
MgCl2 = 30 mg l1
CaCl2 = 85 mg l1

CaSO4 = 28 mg l1
...

[Ans
...
07 ppm; 128
...
blogspot
...
PM5

377

...
3 mg l1; Al2(SO4)3 = 34
...
5 mg l1; NaCl = 29
...

Calculate the amounts of lime and soda to be required for softening the water
...

ENGINEERING CHEMISTRY

y
...
Lime = 3
...
3 kg]
The total hardness of 1,000 litres of water was completely removed by a zeolite softener
...

Calculate the hardness of water
...
384
...

Calculate the lime and soda required to soften 10,000 litres of water sample having calcium
hardness = 450 mg l1 as CaCO3; magnesium = 150 mg l1 as CaCO3 and total alkalinity = 400
[lime = 1
...
6 kg]
mg l1 as CaCO3
...

ni

10
...
5 g of calcium carbonate per litre required 30
ml of EDTA solution
...
Calculate the cost of lime and soda required for softening 1 million litres of a water sample
containing
...

The cost of lime of 80% purity is Rs
...
12,000 per metric ton
...
blogspot
...
PM5

378

sp

378

...

18

ve

rs

Fuels and Combustion

ni

INTRODUCTION

ca

lu

Fuel is a combustible substance, which on combustion produces a large amount of heat, which
can be used for various domestic and industrial purposes
...
Fossil fuels are non-renewable energy resources which were stored up millions
of years ago by photosynthesis
...

Fuels

ch

no

lo

gi

The process of combustion involves oxidation of carbon, hydrogen etc
...

Classification of fuels

Derived

ht
tp
:/
/k
er
al
a

te

Natural

Solid

Liquid

Gaseous

Solid

Liquid

Gaseous

Wood
Coal
Dung

Crude
oil
(Petroleum)

Natural
gas

Coke
Charcoal
Petroleum coke
Coalbriquette

Tar
Kerosene
Diesel
Petrol
Fuel oil
LPG
Synthetic
gasoline

Coal gas
Water gas
Oil gas
Biogas
Coke oven
gas
Blast
furnace
gas

CALORIFIC VALUE
There are different expressions for calorific values:

(i) The quantity of heat evolved by the combustion of unit quantity of fuel is its gross
calorific value (GCV)
...

(ii) Net calorific value (NCV) is the quantity of heat evolved when a unit quantity of fuel
is burnt in oxygen, the original material and the final products of combustion being at a reference
379

http://keralatechnologicaluniversity
...
com

...
The net
calorific value is hence always less than the gross calorific value by the amount corresponding
to the heat of condensation of water vapours i
...
, 587
...

it

= HCV Mass of hydrogen × a × Latent heat of steam
since 1 part by mass of hydrogen produces a part by mass of water
...

∴ NCV = HCV Latent heat of water vap
...
The calorific value is expressed in either calorie/gm (cal/gm) or
kilocalorie/kg (kcal/kg) or British thermal unit/lb (B
...
U/lb) in the case of a solid and a liquid
fuel
...
T
...
/ft3
...
The apparatus which is used to determine the calorific value of
solid and liquid fuels is known as Bomb calorimeter (Fig
...
1)
...
1 Bomb calorimeter
...
Through the lid there is one oxygen inlet valve and two
electrodes
...
The sample of fuel is placed
in the crucible
...
The bomb is placed
in a copper calorimeter, which is surrounded by an air jacket and water jacket which minimises
the heat loss due to radiation
...

A weighed mass of a fuel placed in the crucible is allowed to burn in oxygen by electric
spark across the electrode and the heat liberated is measured by the principle of calorimetry
i
...
, the heat liberated is taken by calorimeter and water
...

Calculation: m = mass of fuel pellet (g)
W = mass of water in the calorimeter (g)

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH18-1
...
c
ot
og

w = water equivalent of calorimeter (g)

y
...

t2 = final temperature of calorimeter
...

it

(W + w) (t2 − t1)
cal/gm
...
The fuels used in the above purpose are benzoic acid (GCV
= 6325 kcal/kg) and naphthalene (GCV = 9688 kcal/(kg)
...
Heat liberated during sparking should be subtracted from heat
liberated
...
Fuels containing Sulphur and Nitrogen if oxidised, the heats of formation of H2SO4 and HNO3 should be subtracted (as the acid formations are
exothermic reactions)
...
The rate of cooling of the calorimeter from maximum temperature to room temperature is noted
...
e
...

lo

gi

ca

lu

ni

ve

rs

L = HCV =

(W + w) (t2 − t1 + Cooling correction) − (Acid + fuse correction)

...

H = 34500 kcal/kg;
C = 8080 kcal/kg;
S = 2240 kcal/kg
Oxygen present in the fuel is assumed to be present as water (fixed hydrogen)
...

8
Dulongs formula for calorific value from the chemical composition of fuel is,
= Total hydrogen

HCV =

LM
N

FG
H

IJ
K

OP
Q

1
0
+ 2240 S kcal/kg
8080 C + 34500 H −
100
8

where C, H, O, S are the percentages of carbon, hydrogen, oxygen and sulfur in the fuel
...

100

= [HCV 0
...

(Q 1 part of H gives 9 parts of water and the latent heat of steam is 587 kcal/kg)
...
A coal has the following composition by weight C = 90%, O = 3%, S = 0
...
5% and ash = 2
...
Net calorific value of the fuel was found to be 8490
...
Calculate
the percentage of H and GCV
...
blogspot
...
PM5

381

sp

381

FUELS AND COMBUSTION

...
09 H + 587) kcal/kg
= (8490
...
09 H + 587) kcal/kg
[Q H = % of hydrogen]
= (8490
...
8 H) kcal/kg
...

Sol
...
5 kcal/kg
...
8 + 345 H = kcal/kg
...
8 + 345 H = 8490
...
8 H
...
8 + 345 H = 8490
...
8 H
...
2 H = 1335%
∴
H = 4
...
5 + 52
...
575) = 8731
...

Example 2
...
83 g of a solid fuel in a bomb calorimeter, the temperature of
3500 g of water was increased from 26
...
2°C; water equivalent of calorimeter and latent
heat of steam are 385 and 587 cal/g, respectively
...
7% H, calculate HCV
and NCV
...
2 − 26
...

HCV =
=
0
...

NCV = (HCV 0
...
9 × 0
...

Boys Gas Calorimeter
...
18
...

In the apparatus (Fig
...
2) known volume of gas is burnt at a uniform rate by a burner
...
Separate thermometers measure the incoming and outgoing water temperatures
(t1 and t2)
...
18
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH18-1
...
c
ot
og

Let

V = volume of gas burning
...

bl

W = mass of cooling water used in time t
...

L = HCV
...

Latent heat of steam per m3 of gas

NCV = L −

OP
Q

m × 587
kcal/m3
...
Calculate the volume of air required for complete combustion of 1 m3 of a
gaseous fuel having the composition: CO = 46%, CH4 = 10%, H2 = 40%, C2 H2 = 2%, N2 = 1% and
the remaining being CO2
...
Let the gaseous fuel be 1 m3

1
O = CO2
2 2
1
Volume of O2 required = 0
...
23 m3
2
CH4 + 2O2 = CO2 + 2H2O
Volume of O2 required = 0
...
2 m3

ht
tp
:/
/k
er
al
a

te

ch

no

CO +

H2 +

1
O 2 = H2O
2

Volume of O2 required = 0
...
2 m3
2

1
O = 2CO2 + H2O
2 2
5
Volume of O2 required = 0
...
05
2
Total O2 required = (0
...
2 + 0
...
05) m3 = 0
...
68 ×

100 3
m = 3
...

21

SOLID FUELS
Wood

Wood is derived from trunks and branches of trees
...
Wood contains lignocellulosewood pulp mainly consists of α cellulose and a very
small amount of β cellulose, resins and proteins
...
Wood is largely used as domestic fuel, its
use as engineering fuel is restricted
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH18-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

384

Coal

bl

Coal is the most important solid fuel and derived from prehistoric plants
...

ht
tp
:/
/k
er
al
a

te

ch

no

lo

gi

ca

lu

ni

ve

rs

it

y
...
Vegetable matter is first transformed into peat, then to lignite then into
bituminous coal and finally to anthracite
...
The continuity can be proved graphically by plotting oxygen
and C percentages of coal at different stages of formation
...
Various types of coal are ranked according to the degree of
coalification from the parent material wood as follows:
Wood → Peat → Lignite → Bituminous coal → Anthracite
With the progressive transformation of wood, the moisture, H, O, N, S, volatile matter
content decrease whereas carbon content, calorific value and hardness increase
...
Peat is regarded as the first stage of coalification of coal
...
It
is extracted by hand cutting
...

It is used as domestic fuel, in steam boilers, power stations and gas producers
...
Low temperature carbonisation of peat is used for getting peat coke and
byproducts
...

2
...
Lignite is compact in texture,
containing 2060% moisture
...
Its calorific value
is 65007000 kcal/kg
...
It is powdered, dried and pressed into
briquettes and used for domestic purpose, for boilers and for production of producer gas
...
Bituminous coals are black and usually banded with alternate very bright and dull
layers
...
(C content 7078%, H 45% and O 20%)
...
Calorific value is 68007600 kcal/kg
...

(b) Bituminous coal (C content 7890%, calorific value is from 8000 to 8500 kcal/kg)
...
By carbonisation and gasification it is converted to coke, gaseous fuels like producer gas, water gas, coal gas, liquid fuels like
coal tar fuels
...
It ignites
more easily than anthracite
...
Calorific value is 85008800 kcal/kg
...
Anthracite is the highest rank coal having highest percentage of C (9298%), lowest
volatile matter and moisture
...
It burns without smoke but
ignites with difficulty, possesses no coking power
...

Occurrences
...
Bituminous coals are found in Bihar, Bengal, Madhya
Pradesh,Chhattisgarh and Orissa
...

Analysis of Coal
Ranking of coal is done on:
(a) Proximate analysis: It consists of determination of percentages of (i) volatile
carbonaceous matter, (ii) fixed carbon, (iii) ash and (iv) moisture of the airdried coal
...
blogspot
...
PM5

384

...

bl

(b) Ultimate analysis: Consisting of determination of percentages of C, H, O, N and S
...

Other chemical and physical properties are specific gravity, surface area and porosity,
refractive index etc
...
and again weighed
after desiccation till constant weight
...

Wt
...

lu

ni

ve

Percentage of moisture =

Loss in weight
× 100
...
of coal sample taken
(iii) Ash: The residual sample after the two above experiments in the crucible is heated
in the furnace at 700°C ± 50°C for 1 or 2 hours without the lid
...

gi

ca

Volatile matter percentage (V
...
) =

lo

Wt
...

Wt
...
Hence, lower the moisture content, better the quality of coal
...
Low volatile matter also reduces coking property of coal
...
Ash deposition also causes problems in the
furnace walls and the ultimate disposal of ash is also a problem
...

(b) Ultimate Analysis:
(i) Carbon and hydrogen: Accurately weigh 12 gm of the coal sample and burn in a
current of O2 in combustion apparatus whereby CO2 and H2O are formed
...
The increase in weight gives the C and H content as follows:
and 2KOH + CO2 → K 2CO3 + H2O
...
7H 2O
...
KOH × 12 × 100

...
of coal sample × 44

and percentage of H =

237 g

Increase in wt
...

Wt
...
blogspot
...
PM5

385

...
4

...
of coal taken

rs

Percentage of N =

it

y
...
H2SO4, K2SO4 and heated
...

The excess acid is back-titrated with standard NaOH solution
...
of BaSO 4 × 32 × 100

...
of coal sample in bomb × 233

ca

Percentage of S =

lu

ni

ve

(iii) Sulfur: While determining the calorific value of a coal sample in a bomb
calorimeter, the S in the coal is converted to sulfate
...
HCl and BaCl2 solution, which precipitates
BaSO4 which is filtered in a sintered glass crucible, washed with water and heated
to a constant weight
...

lo

(v) Oxygen content = 100 % of (C + H + S + N + ash)

te

Coke

ch

no

Significance: Higher percentage of C and H increases the calorific value of coal and
hence better is the coal
...
Also, O when combined with H in the coal, H available for combustion becomes
unavailable
...

ht
tp
:/
/k
er
al
a

Carbonisation or coking bituminous coal leads to the formation of coke
...
Both soft and hard cokes are obtained by high temperature carbonisation
...

Coke and Coal
• Coke possesses much strength and porosity compared to coal
...
All these properties of coke
make it suitable for metallurgical processes compared to coal
...

Coarsely powdered coal taken in a closed retort and heated out of contact with air leads to the
breakdown of coal with the formation of water, ammonia, other volatile matters, gases and
coke
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH18-1
...
c
ot
og
bl

Table 18
...

Coal

Volatile
part

rs

it

Carbonisation
Residue
coke

ve
ni

ca
250°C

Middle
oil (17%)

300°C
Heavy
oil (71%)

350°C
Anthracene
oil (9%)

Distillates

no

lo

gi

Light
oil (5%)

Gas
carbon

lu

Fractional
distillation

200°C
Residue
Pitch (62%)
C–56%

Coal
gas

Ammoniacal
liquor

Coal
tar

Benzene, Toluene, Xylene, Cumene etc
...

Heavy oil

Cresol, Xylene, Naphthalene etc
...

ht
tp
:/
/k
er
al
a

te

ch

Table 18
...
In this process, coal is heated in steel
retorts at 500°C700°C
...
The coke obtained is not mechanically strong but highly reactive and can
be easily ignited to give smokeless flame and used as a domestic fuel
...

Disinfectants are made from this tar
...
The crude spirit corresponds to crude benzol of HTC
but contains greater amount of paraffins, naphthalene and olefin
...
It is carried out at 900°C1200°C producing coke of good porosity, hardness, purity and strength and can be used in
metallurgy
...
The retorts used are made of brick
...
The calorific value is lower, about 4500 kcal/m3
...
blogspot
...
PM5

387

sp

387

FUELS AND COMBUSTION

...

bl

Distinction between high temperature carbonisation (H
...
C
...
T
...
) at a glance:
• Temperature
⇒
L
...
C
...
T
...
= 10001400°C
• Economy
⇒
In L
...
C
...
T
...
retorts made of
fire bricks are used
...
T
...
than that of
H
...
C
...

• Nature of tar
⇒
The liquid volatile products are larger in
quantity in the case of L
...
C
...
T
...
The formation of lower
amount of paraffin and alicycilc compounds and
higher amounts of aromatic compounds in the
case of H
...
C
...
T
...

• Nature of other products
⇒
The amount of ammonia formed greatly
increases with the rise of temperature showing
that nitrogenous complexes are broken at
higher temperature
...
1 and 18
...

• Physical characteristics of tar ⇒
H
...
C
...
T
...
tars
...
T
...
tar per ton of coal is much
greater than that of H
...
C
...

There are two main types of oven for the manufacturing of coke:
(a) Beehive oven: It is a batch process and now obsolete
...
5 m diameter and form the shape of a beehive
...
Coal forms a layer of 6090 cm depth
...
Heat is
supplied by the burning of the volatile matter and hence no byproducts are recovered
...
At the end of carbonisation, the coke is quenched by water and raked out
through the side door, leaving the oven hot enough to start the next batch
...
18
...

Coal charging
door

Heat radiated
from the roof to
the coal bed

Refractory lining
Zone of combustion

Coal

2
...
6 m

Door for
air supply for
coke discharging

4m

Fig
...
3 Beehive coke oven
...
blogspot
...
PM5

388

...

bl

The limitations of the process are (i) no recovery of byproducts, (ii) coke yield is low,
(iii) the exhaust gases cause pollution, (iv) process is not flexible
...
The thermal efficiency has been increased and
the valuable byproducts are recovered
...
The batch process is made continuous by
building ovens in a battery
...
4 m) erected side by side with vertical flues in between them
...
It is heated externally by a portion of coal gas produced by the process
itself or by producer gas or by blast furnace gas
...

• Beehive coking is obsolete
...

A portion of coal is burnt inside the retort to generate heat for coking
...

ht
tp
:/
/k
er
al
a

te

ch

no

Finely crushed coal is charged through the hole at the top and in a closed system it is
heated to 1200°C
...
The flow of heating gases is then reversed and
the hot checker bricks heat the inlet gas
...

Carbonization takes about 11 to 18 hours, after which the doors are opened and the glowing
coke mass is discharged by machine driven coke-pusher into coke-quencher
...
Dry quenching is also done by circulating flue gases
over hot coke and the hot gases are utilised to run waste heat boilers (Fig
...
4)
...
18
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH18-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

390

y
...
Tar and
steam get condensed
...

it

(i) Coal tar is condensed in the tank below
...

ve

(iv) Benzene is recovered similarly by spraying petroleum
...

Fe2O3 + 3H2S → Fe2S3 + 3H2O

ni

(v) H2S is recovered by passing the gas through moist Fe2O3 as:

lu

Fe2S3 is again regenerated by exposing to atmosphere
Fe2S3 + 4O2 → 2FeO + 3SO2

ca

4FeO + O2 → 2Fe2O3

lo

gi

Beehive ovens are located in Jharia, Raniganj, Bokaro-Ramgarh in large numbers in
India whereas byproduct coke ovens are on large numbers in Giridih, Durgapur, Jamshedpur,
Bhilai, Rourkela, Bokaro etc
...
Sulfur, nitrogen and oxygen are present in
the form of derivatives of hydrocarbons in the oil
...
53%, N ⇒ 0
...
Practically all metals are
found in petroleum, the most common are Si, Fe, Al, Ca, Mg, Ni
...
The dead organic matter settles down to the bottom of shallow seas and
lagoons
...

Classification of petroleum
...

(b) Asphalt-base crude contains mainly naphthenes and cycloparaffins with smaller
amounts of paraffins and aromatics
...

About 90% crude produced at present fall in this last category
...
By
the hydrostatic pressure of natural gas the oil is pushed up or it is pumped up by means of a
pump
...
This crude oil is sent to the
refineries for further processing and refining of the crude oils (Fig
...
5)
...
blogspot
...
PM5

390

...

bl

Compressed
air
Oil

Natural
gas

ve

Natural gas

ni

Brine

lu

Fig
...
5 Mining of crude oil and use of air-lift pump
...
All these steps are
under petroleum refining which include:
1
...
Crude oil is intimately mixed with water forming an emulsion
...

2
...
Sulfur compounds have objectionable
properties of pollution so they are removed prior to distillation as copper sulfide by treatment
with copper oxide
...
Petroleum distillation
...
These are separated in a fractionating column consisting of a tall tower where the
higher boiling fractions condense first
...
18
...
3)
...
18
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH18-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

392

it

y
...
The naphtha is condensed and subjected to refining
for the removal of sulfur, diolefins after refractionating
...

Its calorific value is 14,250 kcal/kg and is used as a fuel for internal combustion engines
in automobiles and aircrafts
...
This contains
some gasoline, which is passed back to the main fractionating column
...

(c) Kerosene oil is obtained between 250°C300°C
...
Bottom liquid is refined and finally can be used as
domestic fuel having calorific value of 1100 kcal/kg
...
This is passed through a cooler and then
extracted with liquid SO2 to remove sulfur
...

(e) The residual liquid coming out from the bottom on subsequent treatment yields
lubricating oil, vaseline, grease, paraffin wax, asphalt-bitumen, petroleum, coke etc
...
3: Common fractions from crude
Fraction

Boiling range
Within 30°C

ch

no

Uncondensed gas

Composition

Uses

C1 to C4

As domestic or industrial fuel
under the name LPG (Liquefied
petroleum gas)

C5C7

As a solvent
...
e
...
The
chief application of commercial cracking in all the refineries is for the production of gasoline
from gas oils
...
The
surplus of heavier petroleum fractions are also cracked to get petrol
...

1
...
The important reactions are decomposition, dehydrogenation, isomerization and
polymerization
...
wt
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH18-1
...
c
ot
og

CH3(CH2)8CH2 → CH3(CH2)4CH3 + CH3CH2CH = CH2
n-hexane

butene-1

bl

n-decane

it
rs

2CH3CH2CH = CH2

y
...

CH3 CH3


CH3CH2 C C = CH 2

CH 3

lu

ni

ve

This cracking taking place at 475°C530°C temperature leads to liquid phase thermal
cracking
...
When the cracking oil is vaporized
and then cracked at 600°C750°C at a low pressure, it is called vapour phase thermal cracking
...

ca

2
...
The use of catalyst during cracking accelerates the reactions
and at the same time modifies the yield and the nature of product
...

gi

There are two main types of catalytic cracking:

ht
tp
:/
/k
er
al
a

te

ch

no

lo

(a) Fixed-bed catalytic cracking: The catalysts are fixed in towers, through which the
hot oil (500°C) flows from the top and passes down
...
This carbon deposits on the catalyst beds
...
The gasoline is stripped off dissolved gases and purified
...
18
...

Cracked
vapour

Catalyst

Heavy
oil charge

Cooler

Stabilizer
Gases

Vapour
Gasoline

Heater
Catalyst
chamber
(425°C –
450°C)

Pre-heater
(425°C –
450°C)

Fractionating
column

Heavy
oil

Gasoline
+
some dissolved gases

Fig
...
7 Fixed-bed catalytic cracking
...
The preheated heavy oil is forced through
tower along with the fluidised catalyst
...
The catalyst powder
is retained and sent back
...
18
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH18-1
...
c
ot
Light
fraction

Cyclone

600°C

Gases

it

Regenerated
catalyst

500°C

rs

Catalyst
regenerator

Gases

Reactor

Heavy
oil

pe

nt

Catalyst
+ oil

ca

tal

ys

ni

+s

Fraction
matching
column

t

lu

Air

ve

Spent
catalyst

Feed
oil

bl

Cooler

y
...
18
...

Advantages of catalytic cracking:

no

lo

(i) The quality and yield of petrol is better
...

ch

(iii) Operating pressure is lower
...

te

(v) Due to higher aromatics content, the anti-knocking properties are higher
...

ht
tp
:/
/k
er
al
a

(vii) Gum-forming compounds are very low
...

(ix) Only the high-boiling hydrocarbons and the side chain of the aromatics are decomposed preferentially
...

• Gasoline contains alkanes C5C10 atoms
...

• Oil refineries use catalytic cracking to make gasoline
...

• The octane number scale was devised by Thomas Midgley (1889-1944) and he
discovered anti-knocking additives based on lead i
...
, T
...
L
...

(contd
...
blogspot
...
PM5

394

sp

394

...

(i) Cracking not only makes small molecules but also forms branched chain
hydrocarbons
...

rs

(iii) Reforming turns cyclic alkanes into arenes such as benzene and toluene
...
Compounds such as MTBE (Methyl Tertiary
Butyl Ether) now known as 2-methoxy-2-methyl propane
...
Polymerization, alkylation and isomerization
...
These compounds undergo polymerization either in presence of catalyst
(catalytic polymerization) like phosphoric acid, H2SO4 or by heating at temperatures of 500°C
600°C and pressure (thermal polymerization) to yield products rich in branched-chain
hydrocarbons
...

ch

CH3C(CH3) = CH2 → CH3C(CH3)2CH2C(CH3) = CH2
di-isobutene

te

iso-butene

ht
tp
:/
/k
er
al
a

Similarly, alkylation in presence of HF or H2SO4 gives iso-paraffins
...
All these processes
supply excellent high volatile gasoline components
...
Reforming
...
This upgrading is a result of
reforming of molecules without disturbing their average molecular weights, like formation of
aromatics from naphthene and paraffins
...
Actually these aromatics and the iso-paraffins are the best
gasoline components
...
blogspot
...
PM5

395

sp

395

FUELS AND COMBUSTION

...
Thermal reforming has
been almost completely replaced by catalytic reforming
...

The catalysts used are molybdena, chromia supported on alumina, platinum on silica or
alumina
...

rs

it

Reforming is a once through process
...
18
...

ni

Low boiling
(to avoid explosive
reaction with H 2 )

ve

H 2 compressed
and recycled
Diethanolamine
(DEA)

ing catalytic bed
(Pt–Al 2 O 2 )

Fraction
b
...

100–170°C
Residue

Reactor
(Pt–
Al 2 O 3 )

gi

Heater
Reactor
at 500°C contain-

lo

Gasoline
feed stock

Fractionator

Heater
at 500°C

Fractionator

Reformed
or
stabilized
gasoline

Reactor
(Pt–
Al 2 O 3 )

Condenser

To
solvent
DEA
recover

Heater
at 500°C

ch

no

H2S
scrubber

ca

lu

Compressor
(25 atm)

Gas

Fig
...
9 Fixed-bed catalytic reforming process
...

The former leads to gum and sludge formation and the latter leads to corrosion of engines and
pollution of atmosphere
...

(i) Objectionable odour forming mercaptans and H2S make the oil sour
...
The black PbS precipitates and the other disulfides are
extracted with a suitable solvent, rendering the foul smelling stock to sweet smelling
or odourless stock and the process is called sweetening process
...

(iii) The storing quality of the refined gasoline is improved by adding different inhibitors
of oxidations to it
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH18-1
...
c
ot
og

sp

397

FUELS AND COMBUSTION

Knocking

it

y
...
Maximum power is derived from gasoline when it burns silently and
uniformly in an internal combustion engine
...
This is known as knocking
...

rs

The anti-knock quality of a fuel is expressed as its octane number
...
The hydrocarbons present influence the knocking properties
of gasoline which vary according to the series: straight chain paraffin > branched chain paraffin
> olefin > cycloparaffin > aromatics
...

lo

gi

The most effective antiknock agent added is tetraethyl lead (TEL) along with ethylene
dibromide which prevents the deposition of lead by forming volatile lead halides
...

ch

no

1
...
5 ml of TEL is added per litre of petrol
...

Cetane Number

ht
tp
:/
/k
er
al
a

te

There is a delay period between the injection of diesel fuel and its ignition
...
This delay period is connected to the type of hydrocarbons present in the
diesel
...
The order is the reverse for gasoline anti-knock quality
...
If a given
fuel matches in quality with the blend having 40/60 blend of cetane and α-methyl naphthalene,
it is assigned a cetane number 40
...

Liquid Fuel from Coal and Coal Tar
The conversion of coal into oil is essentially raising the H:C ratio
...
Bergius-Pier Process: Destructive hydrogenation of coal in presence of a catalyst
yields oil, but it is not yet competitive with petroleum refining
...
The paste is preheated and treated with H2 at 250350 atm
...
The unreacted coal is filtered-off and the liquid product distilled
...
The crude oil is fractionated to get (i) gasoline
(ii) middle oil and (iii) heavy oil which is recycled
...
Yield of gasoline is 60% of the coal dust
...
blogspot
...
PM5

397

...

Condenser

it

Gases

Catalyst
(Sn or Ni
oleate)

bl

Powdered
coal
Heavy
oil

Fractionating
column

ni

Crude
oil

ve

Heavy
oil

Converter at
450°C and 200 – 250 atm

lu

Fig
...
10 Bergius process of hydrogenation of coal to gasoline
...
Fischer-Tropsch Process
...

te

ch

The gas is purified by passing over Fe2O3 to remove H2S, then passing over a mixture of
Fe2O3
...
The purified gas is compressed to 5 to 25
atm
...

ht
tp
:/
/k
er
al
a

The exothermic reaction leads to the formation of straight-chain saturated and
unsaturated hydrocarbons
...

The gasoline contains straight chain hydrocarbons and hence have low octane number,
so needs reforming before use (Fig
...
11)
...
18
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH18-1
...
c
ot
og

Important Petroleum Products

ch

no

lo

gi

ca

lu

ni

ve

rs

it

y
...

Gasolines
...

Motor gasoline is a mixture of low boiling hydrocarbons (215°C) and made by blending
(i) Straight run gasoline (direct distillation of crude oil), (ii) cracked gasoline, (iii) reformed
naphtha and other fractions, 10% butane for easy starting of engines, TEL and other additives
...

Aviation gasolines have higher volatility and higher percentages of TEL and isoparaffin
...
Kerosene is used for domestic purpose, space heaters for jet engines
...
No additives are required
...

Diesel fuel
...
It is rich in aromatics and iso-paraffins, the low cetane number is improved by
additives
...
In a high-speed diesel engine,
the cetane numbers should be more than 45 whereas for low speed engines it should be in the
range of 25 to 35
...
Wide range of liquid fuels used in boilers and furnaces are covered by this
term
...
The
heavy fuel oil produced from the cracking units are the heavy variety
...
Liquefied petroleum gas is obtained as a byproduct during the cracking of heavy
oils or from natural gas
...
They are n-butane, isobutane, butylene, propane
etc
...

Non-petroleum Fuels

ht
tp
:/
/k
er
al
a

te

1
...
Refined benzol is essentially a mixture of 70% benzene, 18% toluene and 6%
xylenes
...
It is a good fuel for internal combustion
engines but its initial boiling point is high (80°C), so it can be used only when blended with
gasolines
...

Alcohols
...
Cost considerations
prohibit their use
...
But their calorific values
are low
...
It serves to increase the octane rating
...
It requires about 36 hrs
...

GASEOUS FUELS

(a) Fuel gas from nature:
(i) Natural gas
(ii) Methane from coal mines
...

(d) Fuel gas made by fermentation of organic wastes
...
blogspot
...
PM5

399

sp

399

FUELS AND COMBUSTION

...

bl

Natural gas is a mixture of paraffinic hydrocarbons and methane is the principal
component
...
Water, dirt, H2S, CO2, N2 and
heavier hydrocarbons are removed from the gas and finally it contains from 50 to 95% methane,
5-10% ethane, 3% H2 etc
...

Natural gas is used (i) as a domestic fuel, (ii) for manufacture of various chemicals
(iii) as raw material for the manufacture of H2 and carbon black and (iv) for synthetic protein
preparation from methane
...
Its calorific value is around 5000 kcal/m3
...
It burns with a long smoky flame
...
Tar and ammonia
are first removed by cooling the gas and water scrubbing, then benzol, naphthalene are removed
by creosote oil scrubbing, H2S is finally removed by passing it over moist ferric oxide
...

Producer Gas

ht
tp
:/
/k
er
al
a

te

ch

no

It is a mixture of combustible gases like CO and H2 and large amount of non-combustible
gases like N2, CO2 etc
...
It is a fuel of
low calorific value (1300 kcal/m3) but its advantage is its cheapness and ease of production
...
can be used
...

The dimension of the vessel is about 4 m height and at the top there is a cone feeder and a side
opening for producer gas outlet
...

Coke
Cup and
cone feeder
Producer
gas outlet

Distillation zone

Refractory
brick lining

Reduction zone
Combustion zone

Coal at
1000°C

Air mixed
with a little
steam

Exit for
ash

Fig
...
12 Gas producer
...
blogspot
...
PM5

400

...

bl

Reaction Zones in a Gas Producer
(a) Ash zone
...
The air-steam
blast is preheated by the ash zone which also protects the grate from intense heat
...
This is just next to the ash zone
...
CO2 forms at the expense of O2
...
The temperature at
this zone is about 1100°C
...
5 kcal
2
(c) Reduction zone
...
Its equilibrium constant greatly
increases with rise in temperature
...
The temperature is around 1000°C
(d) The uppermost layer of the bed is the drying and carbonisation zone
...

The topmost zone serves to preheat the precarbonised fuels coming in
...
The average composition of the producer gas is CO: 22-30%, H2:
8-12%, N2: 52-55%, CO2: 3%
...

For the production of producer gas, only air can be used, steam used along with air is
advantageous since (i) it raises the content of combustible components (CO + C2) compared to
noncombustible thereby increasing calorific value, (ii) the endothermic reaction of steam and
C prevents localised overheating of a fuel bed and leads to diminished clinker formation
...
The equipment is known as water
gas generator and is more or less similar to that shown in Fig
...
12 where the following
reaction takes place which is endothermic
C + H2O → CO + H2 29 kcal
Cup and
cone feeder

Coke
Water gas
outlet
Red hot coke
at 900°C–1000°C
Grate

Steam
supply
Refractory
brick lining

Air supply
Ash
outlet
Ash

Fig
...
13 Water gas production
...
blogspot
...
PM5

401

...

bl

This gas burns with a blue flame owing to high carbon monoxide content and hence
known as blue water gas
...
As the reaction
is endothermic temperature gradually falls and when it comes to 1000°C the blast of steam is
stopped and air blast is passed and the following exothermic reactions occur
...
After the production, ash is removed and the generator recharged
...

The average composition is H2: 51%, CO: 41%; N2: 4%, CO2: 4%

gi

ca

lu

ni

Blue water gas is used as a source of hydrogen, as a fuel gas
...

Products of
combustion

lo

Purge
steam

Oil
spray

ch

no

Steam

Blast
of air

ht
tp
:/
/k
er
al
a

te

Tar separator
Cooler
Purifier

Fig
...
14 Manufacture of carburetted water gas
...
O
...
value (Feed stock) are digested anaerobically to produce biogas
...
The chief constituent of biogas is methane, so the process is also called
biomethanation
...
001-2

H2

0
...
1-4

O2

0
...
5

CO

0
...
blogspot
...
PM5

402

...

• pH = 6
...
2
• Anaerobic condition
...

ve

rs

Arrangements for Biomethanation
Feed stock is mainly cowdung
...
18
...
Higher percentage
of oxygen is also undesirable as an increase in 1% oxygen content decreases the calorific value
by about 1
...

ht
tp
:/
/k
er
al
a

te

Method of Analysis of Flue Gas
Analysis of flue gas will indicate the complete or incomplete combustion of a fuel; which
is very essential in respect of efficient utilization of the fuel
...

Description of the Apparatus
It consists of a water jacketted measuring burette, connected in series with the absorption
bulbs containing the above three solutions successively as depicted in the Fig
...
16
...
The absorption bulbs are filled with
glass tubes for better absorption of the gases
...
blogspot
...
PM5

403

sp

403

FUELS AND COMBUSTION

...

Stop cock

rs

Filter

bl

og

ENGINEERING CHEMISTRY

sp

404

Bulb
containing
KOH
solution

Graduated
Burette

Rubber
tube

ca

Fused CaCl 2

Bulb
containing
Alkaline
pyrogalic
acid

lu

Bulb
containing
AM
...
18
...

te

ch

no

• The flue gas (100 ml) is taken in the apparatus in the measuring burette by adjusting
the volume by water reservoir atmospheric pressure
...
The gas is finally taken in the burette and the volume of the gas is
measured by making the levels of water inside the burette and water reservoir equal
...

ht
tp
:/
/k
er
al
a

• The stopper (2) is opened and provided as usual to get the percentage by volume of O2
in the flue gas
...

• The sequence of the bulbs should be strictly followed
...

• The greater percentage of O2 in the flue gas indicates that O2 supply is in excess
...

SOLVED EXAMPLES

Example 1
...
92 g
Weight of water taken (w) = 550 g

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH18-2
...
c
ot
og
y
...

Rise in temperature (t2 t1) = 2
...

L = 580 cal/g1
...

(2,200 + 530) × 2
...
92
= 7168
...
09 H × L) cal/g1
= (7168
...
09 × 6 × 580) cal/g1
= 6,855
...

Example 2
...
5 g was weighed in a silica crucible, after heating for 1 hr
...
415 g
...
at 1000°C
...
528 g
...
245 g was obtained
...

Sol
...
5 2
...
085 g

lo

gi

ca

lu

ni

ve

rs

=

no

0
...
4
2
...
415 1
...
887 g
...
887 × 100
= 35
...
5
Weight of ash
× 100
% Ash =
Weight of coal
VCM =

ht
tp
:/
/k
er
al
a

So, %

0
...
48%
2
...
528 0
...
283 g

=

Fixed carbon

1
...
32%
...
5
Example 3
...
83 g of a solid fuel in bomb calorimeter, the temperature of
3,500 g of water increased from 26
...
2°C
...
If the fuel contains 0
...

% Fixed carbon

Sol
...
2 − 26
...
83
NCV = (HCV 0
...
09 × 0
...

HCV =

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH18-2
...
c
ot
og

ENGINEERING CHEMISTRY

2

4

acid solution
...

FG N IJ H SO
H 10 K

bl

Example 4
...
1 (N) NaOH was required
...

Sol
...
This (NH4)2SO4 during soiling with alkali liberates

rs

FG N IJ
...

H 10 K

ve

NH3 that is absorbed in H2SO4

ni

The volume of H2SO4 consumed by NH3 (25 ×
...
1) ml (N) = 1 ml (N)
Now, 100 c
...

14
gN = 0
...
014 g Nitrogen is present in 1 g coal
...
014
× 100 = 1
...

So, % of N in the coal sample =
1
Example 5
...
5%; C4H8 = 2
...

Calculate (i) air to fuel ratio and (ii) volume of dry products of combustion using 40%
excess air
...
Basis: 1 m3 of gaseous fuel
...
c(N) H2SO4 =

ht
tp
:/
/k
er
al
a

Volume of
combustible
gases (m3)

te

ch

no

lo

gi

ca

∴

Reaction

Volume of O2 m3

1
= 0
...
3 × 2 = 0
...
30

1
O2 = H2O
2
CH4 + 2O2 = CO2 + 2H2O

C2H6 = 0
...
045

C2H4 + 3O2 = 2CO2 + 2H2O

0
...
135

CO2 = 0
...
09

C4H8 = 0
...
025 × 6 = 0
...
025 × 4 = 0
...
06

CO +

1
= 0
...
06 × 1 = 0
...
24

H2 +

1
O2 = 2CO2 + 3H2O
2

1
O = CO2
2 2

0
...
11 ×

0
...
385
2

Total = 1
...
02

m3

Net need
= 1
...
3
CO 2 = 0
...
22

Total = 0
...
08 m3
Net CO 2 = 0
...
blogspot
...
PM5

406

sp

406

...
333 m3
21
100
∴
air: fuel = 9
...
(i)

Composition of product of combustion on dry basis
...
33IJ OP + FG 9
...
4IJ m
K
100
H 100 K Q H

3

= 8
...

1
...
85 + 0
...
82 × 100
= 9
...
782
7
...
95%
N2 =
8
...
559 × 100
= 6
...

O2 =
8
...
Calculate the volume of air required for complete combustion of 1 m3 of a
gaseous fuel having the composition
CO = 46%, CH4 = 10%; H2 = 40%
C2H2 = 2%; N2 = 1% and the remaining being CO2
...
Basis: 1 m3 of the gaseous fuel
...
46

Volume of O2 required (m3)

Reaction

1
O = CO2
2 2
CH4 + 2O2 = CO2 + 2H2O

CO +

ht
tp
:/
/k
er
al
a

CH4 = 0
...
4

H2 +

C2H2 = 0
...
23
2
0
...
20
0
...
20
2
5
0
...
05
2

0
...
68 m3
required

As air contains 21% of O2 by volume

FG
H

∴ Volume of air required = 0
...
238 m3
...
1
...
It is a carbonaceous residue obtained from the destructive distillation of coal,
petroleum and coal tar pitch
...
The main source
of coke is coal
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH18-2
...
c
ot
og

ENGINEERING CHEMISTRY

Q
...
What is a fluidised bed?

y
...
Finely divided solids suspended in a moving gas or liquid behave like a fluid
...

Q
...
It is a highly complex mixture of paraffinic, cycloparaffinic (naphthenic) and
aromatic compounds with traces of N, O and low percentage of S and is obtained from
underground
...
4
...
It is a refined petroleum product 90% of which distils below 240°C and 10% distils
below 175°C
...

ca

lu

Q
...
What is flash point?
Ans
...
g
...

Q
...
What is an anti-knocking agent?

lo

gi

Ans
...
Most common is TEL (-tetraethyl lead)
...

Q
...
What are Octane Number and Cetane Number?

ht
tp
:/
/k
er
al
a

te

ch

no

Ans
...

Q
...
What is aviation gasoline?
Ans
...
e
...
The main components of aviation gasoline are isoparaffins and
some TEL
...
9
...
Gasoline obtained by direct distillation of petroleum without using other conversion
processes like cracking is known as straight run gasoline
...

Q
...
(a) What is LPG? (b) What is LNG?
Ans
...

(b) LNG is Liquefied Natural gas
...
11
...
See text page 395
...
12
...
See text page 378
...
13
...

Ans
...
The following
examples are a few of the more important basic reactions
...
C 15 H 30
...
blogspot
...
PM5

408

sp

408

...

y
...
AlCl 3

C
¾C ¾ C ¾ C ¾
Branched chain

ch

Straight chain

C

Isooctane

gi

• Isomerisation

¾C ¾ C ¾ C ¾ C ¾ C ¾

ca

¾C¾

te

• Hydroforming or Aromatisation
CH 3

CH 3

ht
tp
:/
/k
er
al
a

(i)

( ii )

sp

409

FUELS AND COMBUSTION

CH 3 (CH 2 ) 5 CH 3
n-heptane

D
cat

+ 3H 2

CH 3

+ 4H 2

Q
...
What is Benzol?
Ans
...
p
...
It is blended with petrol
...
The blended
petrol is a good motor fuel
...
15
...
Ethyl alcohol when blended with petrol to be used as a fuel for internal combustion
engine, is known as power alcohol
...
16
...
It is a mixture of gasoline and alcohol
...

The use of grain alcohol as a blending agent with petrol is a controversial issue in the
world
...
Moreover, rectified spirit
(95% alcohol) is not suitable for blending, 99
...
That is why now-a-days butanol is tried for the purpose
...
blogspot
...
PM5

409

...
17
...

bl

Ans
...
But other oils like diesel and
heavy oils and petrol may also be used for cracking
...
The oil is cracked to lower
gaseous hydrocarbons
...
+ tar

rs

The resulting gases are passed generally through a hydraulic main and collected in a
gas holder by displacement of water
...

lu

The gas is mainly generated for laboratory use
...
18
...

• Can be distributed over a wide area by pipeline
...

lo

• The temperature of heating can be controlled by controlling the gas flow to the burner
...

no

Q
...
Mention the disadvantages of a gaseous fuel
...

ch

• Danger of explosion

te

• Larger scale fire risk
...
20
...
The organometallic compounds like TEL or TML, which increase octane number of

ht
tp
:/
/k
er
al
a
a fuel
...
21
...
The variety of gasoline specially suitable for aircraft having octane number well
over 100
...
22
...
1%?

Ans
...

Q
...
What is a natural gasoline?
Ans
...

Q
...
What is HDA process?

Ans
...
This gasoline is mainly used to produce benzene by Hydro-DeAlkylation
(HDA) process
...
blogspot
...
PM5

410

sp

410

...
25
...
It is unleaded gasoline used for motor boats
...

Q
...
Why is calorific value of coal gas higher than that of producer gas?

rs

So calorific value of coal gas is higher than that of producer gas
...
Coal gas contains all the combustible gases like CH4, C2H4, C2H2, CO and H2,
whereas producer gas contains CO, H2 and N2
...

ve

Q
...
Producer gas is made by passing air and steam through a thick bed of
coal
...
28
...
The primary purpose of steam is to use up the heat developed during exothermic
reaction of coal and O2 of air to maintain the temperature of producer
...
Gross calorific value GCV includes the latent heat steam during combustion of a
fuel, but Net calorific value NCV excludes the latent heat of steam
...
29
...
30
...
Ash is inorganic in nature
...

ch

Ans
...

te

Q
...
What is synthesis gas or syn gas?

ht
tp
:/
/k
er
al
a

Ans
...
Two varieties of gas are obtained:
(i) Low heat gas (ii) Medium heat gas
...
These gases are known
as synthesis or syn gas
...
(ii) Entrained
bed
...
32
...
(i) During the production of syn gas, at sufficiently high pressure i
...
, during
hydrogasification H2 liberated converts carbon to CH4
...
But the synthetic product cannot
be known as natural; so now it is called substitute natural gas (SNG)
...
The higher
pressure and lower temperature result in the formation of larger amount of SNG
...
blogspot
...
PM5

411

sp

411

FUELS AND COMBUSTION

...

Pyrolysis
zone

bl

Coal

Distillation
zone

ca

2C + O 2 = 2 CO

lo

gi

Ash bed

Air and steam
blast

EXERCISES

te

ch

no

Fig
...
17 Showing gasification reactions involved in a gasifier
...

Describe the manufacture of producer gas? What are its uses?

5
...

Write the difference between proximate and ultimate analyses
...

Describe the manufacture of biogas from waste materials
...

How is the calorific value of a fuel determined?

9
...

2
...

4
...

(ii) Octane number

(iii) Catalytic cracking
(iv) Proximate analysis
...
What is carbonization? Write the advantages of high temperature carbonization
...
What is power alcohol?
12
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH18-2
...
c
ot
og

sp

413

FUELS AND COMBUSTION

bl

13
...

(b) Explain the terms (i) Knocking (ii) Octane number (iii) Cetane number
...

14
...

(b) What is the flue gas? How is it analysed?

rs

15
...

16
...

ve

17
...

18
...
Give a detailed account of petroleum refining
...
Give at least four advantages of catalytic cracking over thermal cracking
...
What is L
...
G
...

ca

22
...

gi

23
...

24
...
What is power alcohol? Mention its merits and demerits?
26
...

(b) Water gas

ch

(a) Producer gas

no

27
...

28
...

29
...

ht
tp
:/
/k
er
al
a

(i) Catalytic converter

30
...

31
...
What is the difference between H
...
C
...
T
...
?
33
...

1
...

(b) Coal gas

(c) Producer gas
...

3
...

Which of the following contains highest percentage of volatile matter?

(a) Carbon

(b) Sulfur

(a) Peat

(b) Lignite

(c) Hydrogen

(d) Oxygen
...
blogspot
...
PM5

413

(d) Anthracite
...
c
ot
10
...

12
...

og

ni

ve

rs

it

y
...

(c) Water gas
...

(c) C content
...

(c) Isooctane
...

ht
tp
:/
/k
er
al
a

15
...

lu

9
...

gi

7
...

Analysis of flue gases is done by:
(a) Bomb calorimeter
(b) Orsats apparatus
Alcohol-blended petrol possesses
(a) Better calorific value
(b) Reduced antiknock properties
(c) Better antiknock properties
...

Fuel gas used as a source of hydrogen is
(a) Natural gas
(b) Producer gas
Isooctane has an octane rating of
(a) Zero
(b) 100
Better diesel fuel is determined by
(a) Octane rating
(b) Cetane number
Producer gas is a mixture of
(a) CO + H2
(b) CH4 + H2
Fuel for jet plane is
(a) Aviation gasoline
(b) Kerosene
Natural gas is composed of:
(a) n-butane
(b) Methane
Proximate analysis of fuel determines the percentage of
(a) C, H2O, ash and volatile matter
(b) C, H, N, S
(c) C and H
...

ENGINEERING CHEMISTRY

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH18-2
...
c
sp

ot
y
...
Glass was
known to the ancient Egyptians 6000 years ago
...
Ceramic products are made of clay which
are silicates, cement is also a mixture of silicates and other compounds
...

Silicates are chemical compounds of silicon and oxygen with metals
...
Clay must not be confused with soil
...
Soil
is infact a mixture of clay, sand, humus (decayed vegetable matter) and various other minerals
...
Basically
most of these are hydrated silicates of aluminium
...
These tetrahedral units remain joined in the silicates (see Fig
...
1)
...
These silicates are of two types viz
...
Single chain silicates contain [(SiO3)n]2n ion as the primary unit (Fig
...
1),
while double chain silicates contain [(Si4O11)n]6n as the primary unit (Fig
...
2)
...
19
...
e Silicon atom, d Oxygen atom
...
19
...

415
http://keralatechnologicaluniversity
...
com

...
e
...

rs

it

y
...
19
...
These silicates have cyclic structure and contain
[(SiO3)n]2n ion as the primary unit
...
Bentonite is an example: BaTiSi3O9
...
19
...

–
–

–
–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

Fig
...
4 Structure of sheet silicates (layered structure)
...
blogspot
...
PM5

416

...

For that reason the technologies of these industries fall under the common name silicate
technology
...
Now-a-days,
some new types of ceramics are discovered with electrical and magnetic properties
...
These ceramics are called high performance ceramics
...
The property of super-conductivity in these compounds is dependent
on a particular characteristic of arrangements of constituent atoms
...
19
...
The square copper-oxygen sheets are the pathways of superconducting electrons in these compounds
...
The preparation of superconducting ceramic therefore, is an
exacting piece of work
...

bl

•
•
•
•

no

lo

Oxygen
Copper

Ba

Y

Y

Ba

Ba

Ba

Ba

Y

Y

Ba

Ba

ht
tp
:/
/k
er
al
a

te

ch

Ba

Fig
...
5 The crystal lattice of YBa2Cu3O7y
...
blogspot
...
PM5

417

...

bl

These types of superconductors are used in superfast magnetically leviated (maglev)
train i
...
, superfast floating train
...

CEMENT

ht
tp
:/
/k
er
al
a

te

ch

no

lo

gi

ca

lu

ni

ve

rs

it

The present day civilization very much depends upon lime, mortar and cement products, viz
...
The
tremendous application of these products is due to their:
• Convenience
• Cheapness
• Adaptability
• Strength
• Durability
Man had early discovered certain natural rocks
...
Cement was first used by the Egyptians in constructing
the pyramids
...
In 1824, an Englishman, Joseph Aspdin, patented an artificial
cement made by the calcination of an argillaceous lime stone (argil-clay)
...
This was the start of the Portland cement industry as we know it today
...

The cement will set under water and therefore it is known by the name of Hydraulic
cement
...
Two types of
cements are in use
...

Of these, Portland cement is now manufactured on a large scale
...
The raw
materials should be so proportioned as to produce a cement in which the ratio of the amount of
CaO to the amount of (2
...
2 Al2O3 + 0
...
02 and not
less than 0
...
e
...
02
0
...
8 SiO 2 + 1
...
65 Fe 2O 3
The Portland cement is a mixture of the following compounds:
Compounds

Formula

(i) Tricalcium aluminate

(ii) Tricalcium silicate
(iii) Dicalcium silicate
(iv) Tetracalcium alumino ferrate

3 CaO
...
Al2O3
3 CaO
...
SiO2
(CaO2)
...
SiO2
(CaO)4Al2O3
...
Al2O3
...
blogspot
...
PM5

418

Abbreviation
C3A
C3S
C2S
C4AF

...
Some cement
contains gypsum or plaster of paris, which is added in small quantities to increase the plasticity
of cement
...

Varieties of Cement

lo

gi

ca

lu

ni

ve

rs

it

• Portland cement
...
White
cement contains less ferric oxide
...
E
...
It contains a higher proportion of C3S than
regular Portland cement and hence hardens much more quickly
...
E
...
can be put into service more quickly than if regular cement had been
employed
...
A
concrete of better chemical resistance contains high proportion of C4AF
...
A pozzuolana is a material, which is not cementitious in itself but
becomes so upon mixing with lime
...

• High alumina cement
...
It is characterised by a very rapid rate of development
of strength and superior resistance to sea water and sulphate carrying water
...
It is mainly used for the fabrication of corrosion
proof linings for chemical equipment such as storage tanks, absorption towers, acid
digesters etc
...

Raw Materials

ht
tp
:/
/k
er
al
a

te

ch

no

Formerly a large proportion of cement was burned from argilaceous limestone known as
cement rock
...
In addition to natural materials some plants use artificial products such as
blast furnace slag and precipitated CaCO3 obtained as a by-product in alkali and synthetic
ammonium sulphate industry
...
Gypsum (2-3%) is added to prevent rapid setting of the C3A
...

In India, the byproduct precipitated CaCO3 from Sindri Fertilizer Corporation of India
was utilised by A
...
C
...
Rohtas Industries Ltd
...
Limestone is partly replaced
by the CaCO3 mud obtained as by-product during clarification of sugarcane juice at the sugar
factory of the same company
...
e
...
This may involve the raising of the lime
content of the raw materials or it may be for the elimination of the greater part of the silica as
compared to the alumina
...

In making these differential separations, very small quantities of collecting reagents
are employed
...
That is, the
froth floatation process is used to remove the undesirable material in the froth and oleic acid

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH19-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

420

bl

may be employed as the collector
...
04 lb per ton of rock suspended in 4 tons
of water has given good results
...

y
...
For a time it was gradually displaced by the dry
process
...

ca

lu

ni

In the wet process, the solid material after dry crushing is reduced to a fine state of
division in wet tube or ball mills and passes as a slurry through the bowl classifiers or screens
...
This slurry is
filtered in a continuous rotary filter and fed into the kiln
...

no

lo

gi

The dry process is especially applicable to natural cement rock and to the mixtures of
limestone and shale or slate
...
This dry
powdered material (moisture content 2%) is fed directly to the kiln
...
80-160 lbs of fuel are
necessary per barrel (376 lbs) of cement
...
Dry process kilns may be as short as 150 ft, but in the wet process,
300-500 ft kilns are not uncommon
...
The kilns are
rotated at from 1/2 to 2 r
...
m
...
The kilns are slightly inclined so that materials
fed in at the upper end and travel slowly to the lower end, taking from 2-3 hrs (Fig
...
6)
...
Waste heat boilers are used to conserve heat
...
For this
reason, high alumina bricks and high magnesia bricks are widely used for the lining of the
kiln, although Portland cement clinker itself is satisfactory for the purpose
...
SiO2
...
SiO2 + xH2O

Endothermic

CaCO3 → CaO + CO2↑

> 900°C
900°C
to

*5CaO + 3 Al2O3 → 5 CaO
...
SiO2

1200°C

3CaO + SiO2 → 2CaO
...
Al2O3
3CaO + Al2O3 → 3CaO
...
)

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH9-1
...
c
Endothermic

Correcting
tank

Screen

lu

Water

Slurry
mixers

ni

Mills

rs
ve

Oversize
Crushed
shale
limestone

it

*Main reactions between lime and clay
...
Al2O3 and SiO2
...
1 man hr

Mills
Per ton
of
cement

Storage, bagging

Fig
...
6 Wet process for cement manufacture
...
06%;
SiO2 ⇒ 22
...
46%;
MgO ⇒ 0
...
13%
Soda ⇒ 1
...
75%; Unchanged clay and sand ⇒ 2
...

The final product formed consists of hard grannular masses from 1/8 to 3/4 inches in
size, called clinker
...
Pulverising followed
by the fine grinding in tube ball mills and packaging complete the steps to the finished cement
...

• Retarders such as gypsum
• Plaster or calcium lignosulphate
• Air entraining agents
• Dispersing agents and
• Waterproofing agents

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH19-1
...

1250°C

og

421

SILICATE TECHNOLOGY

...

bl

Setting of cement is a complicated process, and the cause of setting has been the subject of
much discussion
...

On addition of water, the calcium compounds are decomposed with the formation of free
Ca(OH)2 and hydrated crystalline silicate and calcium aluminate, the crystals of which form
an interlaced mass
...
The following
equations represent these reactions:
C2S + xH2O → C2S
...
(x 1) H2O (amorphous) + Ca(OH)2
C3A + 6H2O → C3A
...
If this was not true, concrete
would have been rapidly attacked in contact with water
...
6H2O with absorbed water
...
The rapid increase in strength and hardness during setting of cement is mainly due to the
partial hydrolysis of C3S to form needles of Ca(OH)2 in the hydrated silicate gel
...
3CaSO4
...
Al2O3)
...
6H2O(c)
C3A + 3(CaSO4
...
3CaSO4
...
6H2O(c) + CaO
...
(x 6) H2O
MgO + H2O → Mg(OH)2
The various compounds contribute to the heat of setting as follows:
C3A > C3S > C4AF > C2S
Lower heat of setting of cements are made low in C3A and C3S but high in C2S by adding
more Fe2O3, which takes the Al2O3 as C4AF, thereby diminishing the amount of C3A and by
decreasing the CaO/SiO2 ratio
...
As an additional
safeguard, the structure may be cooled during setting by circulating cold water
...

Compounds

Function

C3A

Responsible for initial set (flash set)

C3S

Responsible for 1st strength (after 8 days)

C2S and C3S

Responsible for final strength (at 1 yr)
...

Glass may be considered as supercooled liquid of infinitely high viscosity
...
The liquid glass is cooled until thick enough to mould
and then shaped and cooled further slowly (annealing) until it sets to a solid mass
...
blogspot
...
PM5

422

sp

422

...
Lead glass is used for decorative cut glassware
...

y
...
It is difficult to write any chemical formula for it
...
yMO
...
)
M = bivalent metal (Ca, Pb etc
...

ni

Different varieties of glass

lu

• Vitreous Silica (quartz glass)
...
Used beyond the temperature ranges of other
glasses
...
V
...
V
...
SiO2
...
SiO2)] used in soap manufacture, for preservation of eggs, in the manufacture of
artificial stones
...
CaO
...

ch

Uses
...

(b) Potash lime glass [Bohemian glass, Hard glass] (K2O
...
6SiO2)
...

ht
tp
:/
/k
er
al
a

te

Uses
...

• Lead glass [Potash lead glass, Flint glass]
(K2O
...
6SiO2) fuses easily
...
gr
...
7-1
...
5)
Uses
...

• Borosilicate glass
...
4CaO, 3ZnO
...

Uses
...

Special glasses
1
...
The colouring agents of this group are the oxides of transitional elements,
especially the first group: Ti, V, Cr, Mn, Fe, Co, Ni and Cu
...
blogspot
...
PM5

423

...

bl

• Colour is produced by colloidal particles precipitated within an originally colourless
glass by heat treatment
...

• Colour is produced by microscopic or larger practicles
...

2
...

ve

3
...
When the glass is broken the fragments
are held in place by inter layer
...
Fibre glass

ca

• Glass wool is impregnated with various binders and used for insulation
...

lo

gi

5
...
It can resist
HF
...

no

6
...
This glass has high chemical durability and is
extremely stable to all acids except HF, which attacks more slowly than others
...
On
long standing or very slow cooling during annealing some of metallic silicates crystallise out
...

(c) Hard and brittle
(d) No fixed melting point
(e) Bad conductor of heat and electricity

( f ) Can incorporate colour maintaining transparency
• Chemical:
(a) Not attacked by air, water, oxidising agents, acids
...

Na2O
...
SiO2 + 6HF → CaF2 + SiF4 + 3H2O
(b) Ordinary glass attacked by alkali solutions
...

(b) Fe2O3: Inability to transmit UV is due to the presence of FeO or Fe2O3 in glass
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH9-1
...
c
ot
og

(c) PbO: increases the refractive index of glass
...

bl

(d) B2O3: increases the hardness or refractory characters of glass and lowers expansion
coefficient
...
Substances of an acid character, like SiO2, B2O3
...
Substances of basic character, like soda, potash, lime, MgO, BaO, ZnO, PbO etc
...
Various decolourising and opacifying agents like MnO2, Pb3O4, nitre, Zn-compounds,
SnO2 etc
...
g
...

ca

• Silica is used in the form of sand
...
045%
...
Other sources are salt cake
and NaNO3
...

lo

• The important sources for lime, (CaO) are limestone and burnt lime from dolomite,
CaCO3, MgCO3
...

no

• Potash is always used in the form of K2CO3
...

• BaO as such or as precipitated BaCO3
...

• Boric acid as such or as B2O3
...

• Feldspars having the general formula R2O
...
6SiO2
...
(R2O) and SiO2
...
Devitrification means slow crystallisation
...
It facilitates melting and utilises waste
...

Chemical reactions of the formation of glass in a furnace
Na2CO3 + a SiO2 → Na2O
...
b SiO2 + CO2

Na2SO4 + c SiO2 + C → Na2O
...

• It should be noted that the ratios Na2O/SiO2 and CaO/SiO2 need not be 1:1 molecular
ratios
...
1
...

• In window glass molecular ratios are approximately 2Na2O
...
5SiO2
...
The
green colour due to ferrous silicate being changed to yellow colour due to ferric silicate
...
blogspot
...
PM5

425

sp

425

SILICATE TECHNOLOGY

...

rs

(ii) Shaping
(iii) Annealing

it

The manufacturing procedure is divided into four major phases:
(i) Melting

y
...
Two types of furnaces are in use:

ht
tp
:/
/k
er
al
a

te

ch

no

lo

gi

ca

lu

ni

(a) Pot furnaces (b) Tank furnaces
Pot furnaces are employed principally in the manufacture of optical glass, art glass and
plate glass and in the small scale units
...
2SiO2) or platinum
...

In a tank furnace, batch materials are charged into one end of a large tank built of
refractory blocks
...
The glass
forms a pool in the hearth of the furnace across which the flames play alternately from one
side to the other
...
The operation is
continuous
...

The furnaces may be of either regenerative or recuperative design
...
Once
the furnace has been heated, a temperature 1205°C is maintained all the time
...

This sort of heat loss is necessary to reduce the action of the molten glass on the furnace
wall
...
Sometimes water cooling pipes are used to cool
the furnace wall
...
The glass articles are shaped either manually or by machine
...
It is
allowed to stand vertically on a stand
...
At present every stage of shaping has been mechanised
...

(iii) Annealing
...
Annealing
involves two operations:
(i) Holding a mass of glass above a certain critical temperature, long enough to reduce
internal strain by plastic flow
...

The annealing oven is nothing more than a carefully designed heated chamber in which
the rate of cooling can be controlled
...
All types of glass articles must undergo certain finishing operations
...
Although all these
are not required for every glass object, one or more is almost always necessary
...
blogspot
...
PM5

426

...

Weighing and
feeding the
raw material
to furnace

it

Transportation
of
raw materials

rs

Heat saving by regeneration

Reacting in the
furnace to
form the glass

lu

ni

ve

Shaping
of
glass

Annealing
of
glass products

POTTERY AND PORCELAIN

Burning the fuel to
secure the temperature
needed for glass
formation

gi

ca

Finishing
of
glass products

lo

They are generally clay fired products, sometimes enamelled or glazed
...

Weathering reaction:

ht
tp
:/
/k
er
al
a

K2O
...
6SiO2 + CO2 + 2H2O → K2CO3 + Al2O3
...
2H2O + 4SiO2
feldspar

kaolinite

Common clay

It is principally aluminium silicate mixed up with a large number of substances viz,
compounds of Fe, Mn, Ca, Mg etc
...

Kaolin or China clay
It is a pure white burning clay of low plasticity and is formed by weathering of feldspar
...
2SiO2
...
It contains a good deal of SiO2 and very little Fe
...
Clays are used in the manufacture of
bricks, tiles, porcelain wares, pottery articles, electric insulators, drain pipes and other sanitary
goods etc
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH19-1
...
c
ot
og

ENGINEERING CHEMISTRY

bl

Pottery: (articles made of clay)

y
...

rs

it

Non-porous
(1) China and Porcelain
(2) Earthenware
(3) Stoneware

ve

Raw materials
...

gi

ca

lu

ni

Common fluxing agents
...

Common refractory materials
...
Both glazed and unglazed
clay products are manufactured
...
For glazing the shaped material is covered with a coating of mixture of powdered
feldspar, SiO2, borax etc
...
The thin coating
melts and forms a glaze on the surface of the body
...

In all cases, the unglazed product is to be made
...
China clay

ch

2
...
Flint (Pure SiO2 + CaCO3)

te

4
...
Marble (CaCO3)

ht
tp
:/
/k
er
al
a

6
...

Raw materials for glaze
Frit
...
It is made from Borax, Feldspar, Quartz etc
...
This is a kind of porcelain
...
It is used for sewer pipes
...

Chemical stoneware
...

The reactions of porcelain formation are:
600°C

3Al 2 O 3
...
2H 2 O ¾¾® 6H 2 O + 3Al 2 O 3

+ 6SiO 2

(amorphous)

®¾¾

(amorphous)

China clay

900°C

1000°C

1400°C

SiO 2 ¬¾¾ 4SiO 2 + 3Al 2 O 3
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH9-1
...
c
ot
og

Process: It consists of the following steps:

y
...
Slurry preparation: The mixture of weighed ingredients is taken in a blunger and
stirred well with water to form a creamy liquid known as clay slip
...
Ageing: The slip is filter-pressed
...
The cakes
are dumped for some days
...

rs

3
...

ve

4
...

ni

5
...

gi

ca

lu

6
...
In few cases glaze is put on
the blanks before firing
...
The
firing is done in a tunnel furnace
...

Clay

lo

Storage

no

Water

Screen

Vac

ch

Cutter

Crusher

te

ht
tp
:/
/k
er
al
a

Brick

(a)
Clay

Dinner
plate

flint

water

Vac

Feldspar

Screen

Jigger

Extruder

Slurry
Mag
...
19
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH19-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

430

y
...
The mixture is mixed
with water to make the slip
...

Glaze is a sort of glass, which is applied on the surface to cover the pores
...
All ceramic bodies undergo a certain amount of
vitrification or glass formation
...
Broadly speaking, refractories are
materials which are used to withstand high temperature, chemical and physical effects without
softening or suffering a deformation in shape
...
The main objective of a refractory is to confine heat (i
...
,
to resist the heat loss) and at the same time to resist the abrasive and corrosive action of
molten metals, slags and gases at high operating temperatures
...
Refractories are sold in the form of bricks, silica, magnesite, chromite bricks,
silicon carbide, and zirconia refractories etc
...
These are

ht
tp
:/
/k
er
al
a

te

(i) Acid refractories: They are made of clay, clay-silica mixtures and of pure silica
...
Examplessilica bricks and fire clay bricks
...

ExamplesMagnesite bricks (magnesia), bauxite bricks
...
ExamplesChromite bricks, silicon carbide
and graphite
...
These are self bonded and have
high fusion points
...

Properties

Refractories should possess the following general properties:
(i) They must be able to withstand high temperature
...

The fusion temperatures of the usual refractories in use vary from 1600°C to 2700°C
...

(iv) They should be able to withstand sudden change of temperature
...
e
...
Annealed bricks can better withstand spalling
...
blogspot
...
PM5

430

...

it

y
...
e
...
Decrease in porosity increases the refractorys strength and
also increases its heat capacity, thermal conductivity and chemical strength
...
The reason for such incidence is due to the absence of air in the void space
...
Temp
...

1480–1870°C

te

ch

Deairing by
applying vacuum

Screening to remove
unwanted materials
by settling or
magnetic separation
or chemical method

Mixing, uniform
mixing causes
moulding easy

lo

no

Moulding
1
...
Mechanical

ca

Crushing in jaw
crushers to 25 mm
size of raw materials

ht
tp
:/
/k
er
al
a

Common Refractory Bricks
1
...
During manufacture, silica bricks are heated to about
1500°C within a span of 24 hours
...
During
heating, the quartzite converts to crystobalite
...
So silica brick contains a mixture of tridymite and crystobalite
...
To attain the right
composition 12 hours heating at 1500°C of the bricks is very much essential
...
Fire clay-bricks: Raw material is fire clay (clayAl2O3
...
2H2O)

Generally fire clay bricks contain 55% silica, 35% alumina
...

Basic fire clay bricks contain 55% alumina and 40% silica, rest consists of K2O, FeO, CaO,
MgO
...
blogspot
...
PM5

431

...

bl

Properties
• Light yellow-reddish brown in colour
• Low porosity and lower refractoriness than silica bricks

rs

ve

Uses
• In blast furnaces

it

• Fusion temperature 1350°C
• Crushing strength 200 kg/cm2
• Better resistance to thermal spalling than silica bricks
...

ni

• In kilns
• Charging doors etc
...
High alumina bricks: Composition50% or more alumina
...

no

Uses
• For linings for Portland cement rotary kilns

ch

• Furnace hearths and walls
• In reverberatory furnaces

te

• In combustion zones of oil-fired furnaces
...
Magnesite bricks: Magnesite is naturally occurring magnesium carbonate (MgCO3)
and is the raw material for the magnesite refractories
...
e
...
The prepared powder is pressed into bricks in hydraulic
presses
...

Properties
• They are generally grey or brown in colour
• They can be used upto 1500°C under a load of 3
...

Uses
• For the lining of basic converters and open hearth furnaces in steel industry

• They are used in hot mixer linings, copper convertors
• In reverberatory furnaces for smelting lead, copper
• In refining furnaces for gold, silver and platinum etc
...
Dolomite bricks: They are made by mixing calcined dolomite (i
...
, mixture CaO
+ MgO) in equimolar proportion with silica as binding material
...
blogspot
...
PM5

432

sp

432

...
They are then fired at 1500°C for about
24 hours
...

Properties
• Dolomite bricks are less strong, more porous and have more softness and shrinkage
than magnesite bricks
• They can withstand a load of 3
...

• They are not very much resistant to thermal shock
• They are more resistant to slags and spalling than magnesia bricks
• They wear out quickly
...

6
...
The crushed chromite ore
(FeO
...

lo

• They possess high density, resistance to acidic as well as basic slags
• They can withstand upto 1800°C under a load of 3
...

no

• They possess good crushing strength
• They have moderate thermal conductivities
...
Carborundum or silicon carbide bricks: They are prepared from coke and sand
...
The mixture is then fired at 1500°C in an electric furnace
...
Salt reacts
with iron and similar impurities present in the raw materials to form volatile chlorides
...
The silicon carbides obtained from the furnace
are interlocked tridiscent crystals
...
The
mixture is then shaped, dried and fired
...
At this temperature
interlaced crystals are formed
...
17-3
...
blogspot
...
PM5

433

...

bl

• Resistance to spallationhigh
• Oxidising actionin presence of air at 1000°C silica bricks tend to oxidise to silica
...

• Owing to their high electrical conductivity, they are used in electric arc furnaces
...
Zirconia bricks: Zirconia bricks fall under pure oxide refractories
...

Refractory oxides do not possess plastic properties
...
Organic plasticizers such as dextrin and
resins may also be used
...

Zirconia brick is prepared by heating zirconite (ZrO2)
...
The powdered zirconia is kept under water for sometime and the wet zirconia is
mixed with binding material, viz
...
The materials are
then moulded into bricks by hand moulding or pressing
...

lo

Properties
• Zirconia refractories fall under neutral refractories

no

• They can withstand a temperature upto 2600°C
...

ch

Uses
• Zirconia bricks are very costly

te

• Specially used when high temperature is used

ht
tp
:/
/k
er
al
a

9
...

Properties
• High melting point (2550°C)
• Low electrical conductivity
• High thermal conductivity
• Good resistance to thermal shocks
• Inertness to carbon dioxide and carbon monoxide upto 2000°C
...

• As radiation shields in carbon resistant furnaces
...
Cermets: Cermets are hot pressed or sintered materials comprising ceramic and
metallic components
...
blogspot
...
PM5

434

...

y
...

it

• Most cermets contain about 80% of ceramic materials and 20% of the metal
...

te

ch

no

lo

gi

ca

lu

ni

ve

rs

Uses
• In rocket and jet engine parts
...

11
...
The enamels used to coat metallic surfaces are known
as porcelain enamels
...

For making the enamel at first frit is made from glass forming materials such as sand,
soda ash, feldspar, borax etc; when melted, they form a glass comprising sodium, potassium,
calcium borosilicate
...

Uses

ht
tp
:/
/k
er
al
a

In making:

(i) refrigerators
(ii) food processing equipments

(iii) motor cars
(iv) sanitary wares
...
1
...
A cement is a substance which sets to a hard mass in presence of water
...
2
...
Concrete made with sand, stone chips and cement when reinforced with iron rod
for an extra strength of the concrete is known as reinforced concrete cement (RCC)
...
3
...
The product formed after setting of lime, sand and water is known as mortar
...
4
...

Ans
...
C
...
walls, dams, roads etc
...
blogspot
...
PM5

435

sp

435

SILICATE TECHNOLOGY

...

Q
...
Give general composition of cement
...
5
...
The cement sets under water, that is why the term hydraulic came
...
See text page 418
...
7
...
Glass may be defined

ve

• Physically as an amorphous, transparent or translucent, rigid supercooled liquid of
infinitely high viscosity
...

• Glass has almost 100% elastic recovery
...
8
...
The process of not forming crystals during cooling of glass is called vitrification
...
9
...
Glass-wares left unused for a long time gradually loose their transparency and
become opaque due to the crystallisation of some of metallic silicates of glass
...

no

Q
...
What are ceramics?

ch

Ans
...
Even at the present time ceramics remain
important in many spheres of life
...

te

The greatest uses of advanced ceramic products are in
• Aerospace industry due to their lighter weights compared to metal alloys

ht
tp
:/
/k
er
al
a

• Heat shields for space vehicles
• As bio materials like false teeth; bone replacement, artificial hip joints etc
...
11
...
Refractories are earthy ceramic materials of low thermal conductivity capable of
withstanding extremely high temperature without any change
...
12
...
The primary uses of refractories are for lining
(i) Steel furnaces

(ii) Coke ovens

(iii) Glass wares
...
13
...

Ans
...

Q
...
Mention some refractory metals
...
Tungsten and tantalum (W and Ta) are refractory metals capable to withstanding
high temperatures
...
blogspot
...
PM5

436

sp

436

...

bl

Q
...
Mention some basic refractories
...

• Magnesia
• Chromite
• Forsterite
...
16
...

Ans
...

Q
...
What is the importance of zirconia as refractory?
Ans
...
This
type of zirconia possesses a working temperature of 2600°C
...
18
...

Ans
...
At the early stages of heating, clay undergoes elimination of water of hydration at
600°C
...
2SiO 2
...
At
1000°C, Al2O3 and SiO2 combine to form mullite (3Al2O3
...
As the temperature increases,
more SiO2 is converted to cristobalite
...
2SiO2
...
2SiO2 + 4SiO2 + 6H2O
Mullite

Cristobalite

EXERCISES

1
...

3
...

5
...

7
...

9
...

11
...

Discuss the structural pattern of silicates
...

Distinguish between (a) Pozzuolanic cement and (b) Portland cement
...

Describe the rotary kiln used in cement manufacture
...

How are cements classified? Give the various physico-chemical reactions responsible for the
setting and hardening of Portland cement
...
Describe the setting of mortar and lime
...
Describe various types of cement
...
blogspot
...
PM5

437

...

18
...
Briefly describe its manufacture
...
What is glass? Discuss the physical and chemical properties of glass
...
Classify glasses with composition and illustrations
...
Describe the manufacture of glass by pot furnace process
...
Write short note on soda lime glass
...
Write notes on
(i) Coloured glass
(ii) Plate glass
(iii) Shaping of glass
(iv) Safety glass
(v) Chemical action in glass making
(vi) Fibre glass
(vii) Annealing of glass
(viii) Glass laminates
(ix) Phosphate glass
24
...

25
...
Give reactions involved
...
Write notes on
(i) Clay and common clay
(ii) China clay
(iii) Fire clay
(iv) Uses of clay
(v) Pottery
...
Describe the process of manufacturing of porcelain
...
Give the reaction involved in porcelain formation
...
What are refractories? Give an account of any four characteristics of a good refractory material
...
Explain the theory underlying the manufacture of refractory products
...
Describe the manufacture of:
(i) Fire clay bricks
(ii) Silica bricks
(iii) Magnesite bricks
...
What are basic refractories? Explain magnesite refractory in detail
...
What are fire clay bricks? Describe the manufacture, properties and uses of fire clay bricks
...
What are refractory materials? Write a brief note on chromite bricks
...
Write notes on
(i) Carborundum
(ii) Silica refractories
...
What are refractories? How are they classified? Give examples
...
Explain the significance of the following properties of refractory materials
(i) Porosity
(ii) Dimensional stability
...
State composition, properties and applications of the following materials:
(i) Magnesite
(ii) Fire clay
(iii) Zirconia
(iv) Silica
...

bl

14
...

16
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH9-1
...
c
ot
sp
og
bl

Polymers

ve

rs

it

y
...
g
...

ethylene

C¾C¾C¾C

H H H H
polythene

ch

no

There is no limit to theoretical length of the polymer, but the polymer ceases to grow for
many practical reasons
...

te

Types of polymerization

ht
tp
:/
/k
er
al
a

1
...
Monomers (M) having the general formula,
CH2=CHY (Y=X, CO2R, CN etc
...
e
...
There are three ways of
addition polymerization:
(i) Head to tail type
CH2CHYCH2CHYCH2CHY---(ii) Head to head type
CHYCH2CH2CHY
...
CH2 CH2CHYCH2 CHY---Mechanism of addition polymerization:
(a) Free radical polymerization is the first type which involves the following steps:
Initiation
...
The first is the spontaneous
decomposition of an initiator into free radicals
...

...
blogspot
...
c
ot
og

ENGINEERING CHEMISTRY

sp

440

Free

M

→

M*

y
...

Monomer

it

radical

The M* is the initiator radical or primary radical
...
The mechanism of propagation is the reaction of the radical M* with its
own monomer M
...

gi

→

H H
 
CH2 C  C  CH 2 
 
Y Y

no

lo

i
...
,

H
H


C • + • C  CH 2 
CH2


Y
Y

ca

(i) Collision between two growing chains

lu

Terminations
...

te

(iii) Collision between a growing chain with impurities
...

ht
tp
:/
/k
er
al
a

More rarely, by disproportionation an H atom of one radical is transferred to another
resulting in two polymersone saturated and the other unsaturated
...

Cationic Mechanism
Initiation

X+ + CH2 = CH

Y

→

+

X CH2 C H

Y

The initiators are Lewis acids like AlCl3,BF3, H2SO4 etc
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH20-1
...
c
ot
og
ve

rs

it

y
...

no

Anionic polymerization mechanism:
Initiation:
()

te

ch

Z() + CH2 = CH → ZCH2 C H


Y
Y
Carbanion

Propagation:

ht
tp
:/
/k
er
al
a

sp

441

POLYMERS

(–)

(–)

ZCH2¾CH + CH2 = CH ¾¾® zCH2¾CH¾CH2¾CH
Y

Y

Y

Y
(–)

Z¾CH2CH¾CH2¾CH
Y

n

nCH2 = CHY

Y

Termination:
(–)

+

H
Z¾CH2CH¾CH2¾CH: ¾¾¾® Z¾CH2CH¾CH2¾CH2
Cation

Y

n

Y

Y

n

Y

polymer

Polymerization of olefins with metallic sodium, sodium ethoxide takes place via this
mechanism
...
It was observed by
Ziegler and Natta that in presence of a combination of transition metal halides (TiCl4, ZrBr3,

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH20-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

442

bl

and halides of V, Zr, Cr, Mo etc
...

y
...
Ziegler-Natta polymerization yielded
stereospecific structure of high mechanical strength, unbranched, high melting and highly
crystalline polymer like HDPE (high density polyethylene)
...

ht
tp
:/
/k
er
al
a

H

H

Y

C

C

C

H

H

Y
C

H

Y

C

C

H

H
H
H
(ii) Syndiotactic polymers have similar head to tail arrangements but here Y groups
appear on opposite sides of polymer backbone alternately
...

H
C
H

H
C
Y

H
C
H

Y
C
H

H
C
H

Y
C
H

H
C
H

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH20-1
...
c
ot
og

sp

443

POLYMERS

H

CH3

CH3
CH3

H

H

CH3
CH3

H

H

rs

H

it

CH3

y
...

Atactic polypropene is an amorphous, rubbery polymer of little value unlike isotactic
polypropene (Fig
...
1)
...
20
...

ni

Condensation polymerization

lu

It is the type of reaction occurring between monomers containing polar groups which
form polymer along with the elimination of small molecules like H2O, HCl etc
...

ht
tp
:/
/k
er
al
a

Two or more monomers undergoing joint polymerization is called copolymerization
reaction such as the production of SBR (Styrene butadiene rubber)
...

Strength of straight chain polymers depends on the chain length
...

wt
...
But higher-chain length polymers are tougher and more
heat resistant
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH20-1
...
c
ot
og

ENGINEERING CHEMISTRY

bl

Highlights:

y
...
g
...

• Condensation polymerization:

ve

rs

Combination through different functional groups of monomers with elimination
of small molecules like H2O
...
As for example SBR
...

(b) Ionic mechanism
...

gi

Plastic deformation

lo

Polymers consisting of linear-chain molecules are always soluble and thermoplastic,
even for very high molecular weight
...
Hence, thermoplastic and thermosetting qualities of polymer depend on structure
of the polymers
...

Physical state

sp

444

ht
tp
:/
/k
er
al
a

Random arrangement of molecules in the polymer leads to amorphous state whereas
regular arrangements of molecules or chains in a polymer lead to crystalline state
...
The amorphous
nature of polymer provides flexibility
...

Solubility and chemical resistance

Polymer containing polar groups are more soluble in polar solvents like water, alcohol
but are chemically resistant to non-polar solvents like benzene, toluene, CCl4 etc
...

Shapes and formsmechanical properties
The internal arrangement of the long-chain molecules provides the forms in which the
polymer may form i
...
, fibres, plastics and rubbers
...
If
the internal forces are high they ultimately give rise to orderly arrangement and form fibrous
nature
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH20-1
...
c
ot
og

Stress

bl

Hard, brittle
polymers

it

y
...
20
...

lo

gi

ca

The strength of the polymer is controlled by the length of the polymer chains and its
cross-linking
...
20
...
On increasing strain continuously ultimately the polymer
chains are uncoiled and fully stretched called necking and after this point the polymer reaches
its break point and yields
...
Amorphous polymers, which do
not have melting point have softening points
...
Amorphous polymer becomes rubbery and then gummy
and on further heating it liquefies
...

ht
tp
:/
/k
er
al
a

PLASTICS (RESINS)

Plastics are a class of high polymers which can be moulded into any desired form by
heat and pressure
...

There are two classes of plastics or resins
...
Thermoplastic resins soften on heating and harden on cooling and this change is not
chemical but physical in nature, hence repeated heating and cooling also does not alter its
nature
...
Thermosetting resins are those which are heated during moulding and heating is
continued until is set and hardened
...

Compounding

Plastics for manufacturing of finished articles are always mixed with 4-10% of other
materials, which impart some durable properties to the moulded material
...
The process of mixing these additives to virgin plastics is called Compounding
...
Thermosetting resins are added as linear low molecular weight polymers, which actually form
crosslinking during the moulding process in presence of catalyst
...
blogspot
...
PM5

445

sp

445

POLYMERS

...
Fillers can modify the properties of plastics to give the final plastic, better
hardness, tensile strength, finish and workability
...

Fibrous fillers such as wood flour, cotton fibre, chopped rags impart improved
mechanical strength to the plastic; asbestos increases heat resistance; mica or slate
powder improves electrical properties
...

ve

rs

Solidified filaments of glass are bundled into strands, compressed to produce a glass
mat
...

FRP is very strong and can be used to make gates of dam, corrosion-resistant pipes
and tanks, safety helmets, jeep bodies
...

gi

ca

lu

(iii) Plasticizers
...
Thus, plasticizers act as an internal lubricant and improve the
plasticity and flexibility of the polymer
...

lo

(iv) Waxes, oils, stearates and soaps are used to improve the finish and reduce the sticking
tendency of the plastic to the moulds
...
To improve the appeal and to impart beauty to the finished
materials, colours are added to them
...

ch

To give UV protection to the colours some compounds are added which preferentially
absorb UV light
...
Sometimes antioxidants are added to prevent oxidative degradation
of polymers
...
are
added to accelerate the cross-linking of the thermosetting plastics while they are in
the moulds
...
, are added to improve the thermal
stability of polymers during processing
...
, are added to dissipate the electric charge
developed by conducting it away
...
For production of continuous films or sheets this process is adopted
...
While passing through the gap between the rollers the
sheet is formed, whose thickness varies with the gap
...

(ii) Die casting
...
Compounded material is poured into die cavities made up of metals or
plaster of paris and it is heated when the crosslinking takes place and finally the
finished material is cooled
...
A compounded solution in a suitable solvent is continuously dropped
on a moving belt, the solvent evaporates and films are obtained
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH20-1
...
c
ot
og

Polymer solution

y
...
20
...

ht
tp
:/
/k
er
al
a

te

ch

no

lo

gi

(iv) Compression moulding
...
The mould consists of two halves
...
Heat and pressure applied
...
Finally curing is done by heating (for thermosetting) and cooling (for thermoplastic)
...
, are
made by this process
...
20
...

(v) Injection moulding
...
Plastic powder is fed into a hot cylinder and then injected by a piston plunger into a tightlylocked mould with the help of a screw arrangement
...
The whole
process is automatic
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH20-1
...
c
ot
Top moulding
part (cold)

Plastic feed
Nozzle

Hinge

Heater

Fluidized
plastic

Moulding
powder

Bottom
moulding
part (cold)

ni

ve

Archimedian
screw

rs

it

y
...
20
...

gi

ca

(vi) Blow moulding
...
The mould is
cooled and the article taken out
...
This process is used for continuous moulding of thermoplastics
...
In plastic
condition, it is pushed by screw conveyer into a die whose shape is acquired by it and
finally cooled
...
20
...

(viii) Thermoforming
...
The thermoplastic sheet is heated and softened and placed
between two halves of a metal die
...
Sometimes, vacuum is also applied so that the sheet sticks to the
shape of the mould
...
blogspot
...
PM5

448

sp

448

...

bl

Heating

Vacuum on

Moulded Article

Fig
...
7 Vacuum forming process
...
Ethylene is colorless gas at ordinary temperature
...

Industrially dehydration of ethyl alcohol is the process for ethylene production*
...
The ethylene gas is
compressed to 1500 atmosphere and passed through a reactor maintained at 200°C in the
upper and 120°C in the lower parts
...
01%) or peroxides act as catalyst
...
The unreacted gas is recycled
...
HDPE is produced by using low pressure methods (31 kgf/cm2)
using ionic catalysts whereas LDPE is produced by using high pressure methods (1050-2000
kgf/cm2) using free radical initiator
...
Polyethylene is a rigid, waxy, white, translucent non-polar material
...

* C2H4 → (C2H4)n
Polymerize

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH20-1
...
c
ot
og

ENGINEERING CHEMISTRY

y
...
20
...

Compressor
Fluid-bed
reactor

Cycle
cooler
690 to
2100 kPa
100°C

ht
tp
:/
/k
er
al
a

te

ch

Compressor

Purge

Ethylene
Catalyst

Comonomer

Separator and
product discharge
Lock
Nitrogen
Ganular
polyethylene

Fig
...
9 High-density polyethylene by low-pressure resins (HDPE)
...
The degree of
crystallinity varies from 40-95% depending on degree of branching
...
It has low sp
...
It has low hardness i
...
, about 1/10th
of bakelite
...

Uses
...

It is also used to prepare toys, coated-wires and cables, bags for packing, bottles, caps, insulator
parts
...
blogspot
...
PM5

450

sp

450

...

bl

Polypropylene is obtained by polymerizing propylene in presence of Ziegler-Natta
Catalyst i
...
, organo metallic halide with transition metal halide
...
Polypropylene is also an isotactic, highly crystalline polymer
...
r
...
resistance to chemicals, hardness, strength, moisture proofing quality
etc
...

lu

ni

Uses
...
It is also used for packing of pharmaceutical and
cosmetic products, for making sterilizable hospital equipments, washing machine parts, pipes,
TV, radios, moulded luggage, colorful furniture etc
...

HgCl

lo

CH ≡ CH + HCl → CH2 = CHCl

Polymerize

nCH2 = CHCl ¾¾¾¾® —CH2CHCl—
(
)n
PVC

ht
tp
:/
/k
er
al
a

te

ch

no

The polymerization of the gaseous monomer (b
...
13
...
The polymer is obtained in the form of fine powder and is soluble
only in special solvents like dibutyl phthalate, benzyl benzoate etc
...

Properties: PVC is a colorless, odorless, non-flammable, chemically-inert powder
...

It is resistant to water, light, O2, inorganic acids and alkalies, oil, petrol etc
...

Uses
...
It has high rigidity and chemical resistance but
brittle, so, its use is mainly in making cables, water hoses, toys, rain coats, rexin, pipes of
petroleum industry, floor covering, refrigerator components, tyres, cycles and motor cycle
mudguards etc
...

F

F

Polymerize

n(CF2 = CF2) ¾¾¾¾® —C—C—
F

F

n

Properties
...
blogspot
...
PM5

451

...

bl

properties like extreme toughness, high softening point (350°C), high chemical resistance, low
coefficient of friction and waxy touch, good mechanical and electrical properties
...
It softens at about 350°C, hence at
this high temperature it can be moulded applying high pressure
...
It can be used for insulating motor, transformers, cables, wires etc
...
It can also be used for making gaskets, pump parts,
tank linings, pipes and tubes for chemical industry, non-lubricating bearings and to make
non-reactive coating
...

Properties
...
It has low thermal conductivity
...

Uses
...
Due to its spongy nature, it is
used for making pillows and matresses
...
It is also used to make chairs etc
...
Nylon belonging to this class is used for making fibres
...
blogspot
...
PM5

452

...

bl

Nylon 66 is obtained by the polymerization of adipic acid with hexamethylene diamine
...

ve

Hexamethylene is made by final hydrogenation of the adiponitrile
...
The compounds react to form nylon salt in
solution
...
Nylon fibre is obtained by melt spinning process
...
The polymer can be remelted to spin into fibre and can be used for extrusion of
molded objects
...
Nylon possesses high
abrasion resistance and is chemically stable
...
It is insoluble in common organic solvents but soluble in phenol,
formic acid
...

Important Thermosetting Resins
Phenolic resins
The most important of this class is bakelite or phenol-formaldehyde resin
...
In presence of acid catalyst, the first step leads to the formation
of o-and p-hydroxy methyl phenol, which forms linear polymer
...
blogspot
...
PM5

453

...

+

+ HCHO

Novolac

no

lo

In the second step a small amount of hexamethylene tetramine added and at the steam
temperature, the chain length increases and also three-dimensional resin is formed, which
crosslinks the structure
...

ht
tp
:/
/k
er
al
a

te

ch

OH

CH2

OH

CH2

CH2

OH

OH

CH2

CH2

CH2

OH

CH2

OH

CH2

bakelite

Properties
...
They are resistant to
non-oxidising acids, organic solvents but are susceptible to alkalies
...
These resins possess electrical
insulating properties
...
It can be widely used as metal substitute where high tensile strength is not
necessary
...
It can be used for making insulator
parts like switches, plugs, heater handles
...
It is used as adhesive also used in paints and varnishes, as cation exchanger
resin for water softening, in paper industry as propeller shafts
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH20-1
...
c
ot
og

Monomers are:

y
...
CH2—CH—CH2Cl
OH

lo

gi

CH2 = CH—CH2Cl + HCl

—HCl

ca

Propylene

Epichlorohydrin

ni

(ii) Epichlorohydrins
CH2 = CH—CH3 + Cl2

te

CH3
OCH2CHOH
...
blogspot
...
PM5

455

sp

455

POLYMERS

...

bl

Properties and Uses
Epoxy resins possess outstanding properties of
• Adhesion to various materials
• Flexibility
• Chemical inertness
• Toughness
• Stability at high temperature
• Low shrinkage during cure
...

Polyester

CH2

+ H2O

lu

gi

CH2

¾¾® CH2—OH
CH2—OH

lo

O

ca

CH2
1
O
(a) CH2 = CH2 + – O2 ¾¾®
2
CH2

ni

ve

Polyesters are the condensation products of dicarboxylic acid with dihydroxy alcohols
...
Ethylene is oxidised at high pressure and temperature in the presence
of Ag as catalyst and the ethylene oxide is hydrolysed by dilute HCl to ethylene glycol
...
HNO3 (50%) at about 100°C to give terephthalic acid
...
Better yields
are obtained with dimethylterephthalate
...
Since the structure of the polymer is symmetrical and a number of polar
groups are present it forms fibre easily
...
The fabric made from the fibre is crease resistant
...
It is mostly used for making synthetic fibres like terylene, dacron etc
...

It can be blended with wool and used for making carpets, blankets, upholsteries, quilts etc
...
blogspot
...
PM5

456

...

y
...

it

(ii) Strength
(iii) Crease resistance and

ni

ve

Silicones have alternate silicon-oxygen bonds and organic radicals attached to the silicon
atoms
...

lo

In the next step the chlorides are polymerized by hydrolysis involving the following steps
≡ SiCl + H2O → ≡ SiOH + HCl

te

ch

no

≡ SiOH + HOSi ≡ → ≡ Si O Si ≡ + H2O
Thus, the OH groups of Si are involved in polymerization hence when there is one or
two OH groups in Si, it leads to long chain polymers but when there are three OH groups,
crosslinked polymers are formed
...
SiMe 2 [OSiMe 2 ]n OSiMe 2OH
Silicone

Di-alkyl-di-chlorosilicane and alkyl trichloro silicone undergo hydrolysis and condensation
polymerization to give a cross-linked silicone polymer
...
blogspot
...
PM5

457

...

OP
PP
PP H O
PP →
PP
PP
Q

ve

rs

R
R
R



HO  Si  OH + HO  Si  OH + HO  Si  OH



R
OH
R
R
OH
R



HO  Si  OH + HO  Si  OH + HO  Si  OH



R
R
OH

og

ENGINEERING CHEMISTRY

no

lo

gi

ca

lu

ni

R
R
R



O  Si  O  Si  O  Si  O 




R
R
R
O
R



Si
Si
Si
 O   O  O  O



R
R
O

(Cross-linked polymer)

te

ch

Complete condensation of all the OH give rise to hard, insoluble product, thus a mixture
of monomers (containing one or more OH groups) along with sufficient water for hydrolysis
is heated for polymerization
...
Their properties and uses also differ
accordingly
...
They are of relatively low molecular weight, sparkling clear fluids
with an oily feel, insoluble in water but soluble in aromatic and chlorinated solvents
...

Uses
...

(ii) Silicone greases
...

They are used as lubricants particularly for very high and low temperature applications
...
They are highly cross-linked polymers, possess good insulating
properties, heat resistance and good dielectric properties
...
Used for high voltage insulators, high temperature insulating foams, siliconeglass laminates for high temperature application, for different electrical and electronic
equipment parts manufacturing
...
Silicone rubbers are formed by reaction of dimethyl silicone fluid
with peroxide and appropriate inorganic fillers like TiO2, ZnO, SiO2 etc
...
blogspot
...
PM5

458

sp

458

...

bl

They retain rubbery properties over a much wider temperature span, good heat transfer
properties, good resistance to dilute acids and alkalis
...

Uses
...

Molecular weight of a polymer

ve

rs

Polymers are mixtures of molecules of different molecular masses, since the chain length
varies
...

(i) Number average molecular weight

w
Σ N iM i
=
ΣN
Σ Ni

lu

Mn =

ni

The number average molecular weight ( M n ) is defined as the total mass (w) of all the
molecules of polymer divided by the total number of molecules present
...
Mn can be determined by measuring the
colligative properties like lowering of vapor pressure, depression of freezing point etc
...

Also,

ch

no

Mw =

te

Σ ci M i Σ ci M i Σ N i M i 2
=
=
Σ ci
c
Σ NiMi
where ci = weight concentration of Mi molecules and c = total concentration of all polymer
molecules
...

M w can be determined by light scattering measurements, viscosity measurements,

diffusion measurements
...
5 or larger for natural and synthetic polymers
...

Degree of polymerization
The number of recurring units of monomers in a polymer chain is known as degree of
polymerization (DP)
...
Hence, we use the term average degree

of polymerization ( DP )
...

d(M)
−
= K[M][C] 1/2 M = concentration of monomer
dt
C = concentration of initiator

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH20-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

460

K
...

DP =

bl

At a certain stage of polymerization it is found that the number of active centres for
polymerization is equal to the number of chain terminators
...
The degree of polymerization influences the tensile strength of
the polymer
...

• Cellulose derivatives
• Polythene, Polypropylene, Polystyrene, Polyvinyl chloride,
Polytetrafluoro ethylene (Teflon)
• Polyamides (nylon)
• ABS polymers
...
Examples of this class include
(i) Bakelite obtained by polymerization of phenolic derivatives with aldehydes
...

(iii) Terylene (Polyester) are condensation products of dicarboxylic acids with
dihydroxy alcohols
(iv) Epoxy resins (araldite)
(v) Silicone resins
...
The unstretched rubber is amorphous and the polymer chains are in a
coiled state, which on stretching gets aligned causing crystallization
...

Natural rubber
...
Natural rubber came into market first in early 19th century
...
The latex is
collected from the mature Havea tree by making deep cuts on the bark, and by allowing the
latex stream to collect in a pot attached below the cuts
...

Coagulation of the latex
...
Coagulation is then effected by adding acetic acid (1 to 2% on weight
basis)
...

The coagulum is allowed to drain and the absorbed serum is squeezed out through steel
rollers upon which water is sprayed
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH20-1
...
c
ot
og

sp

461

POLYMERS

y
...
Coagulation is
carried out in large tanks and finally allowed to settle for 16 hours
...
The embossed sheets are then
hung up in a smoking house, where on the floor, wood or coconut husk is burnt to produce heat
...

rs

it

The crude rubber obtained is translucent and amber in colour and is not attacked by
micro-organisms
...
Natural rubber is an amorphous solid, translucent, impervious to gases, elastic
in nature
...

lu

ni

Rubber slowly oxidises when exposed to air
...
It burns
to form CO2 and H2O
...
When the destructive distillation is carried out at higher temperature
the condensate contains mostly the isoprene dimers
...
For each C5H8 unit in rubber molecule, one molecule each
of Br2, O3 and HCl reacts, thus there is only one double bond
...
e
...



CH 3 H

ht
tp
:/
/k
er
al
a

te

ch

During the process of linking, head and tail linking of isoprene molecule occurs
...
Strong HNO3 attacks rubber
...
Also on excessive
streteching it gets permanently deformed
...

Vulcanization of rubber

During 1839, Charles Good Year developed the method of vulcanization of rubber by
which the properties of natural rubber can be improved to a large extent
...
The method is basically heating raw rubber with sulfur at 100° C-140°C,
when the sulfur enters into the double bonds of rubber forming crosslinks between the chains
and this gives the structure toughness
...
For flexible tyre rubber, sulfur content is from 3-5% whereas
for tougher variety like ebonite, content of S is 32%
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH20-1
...
c
ot
og

ENGINEERING CHEMISTRY

Raw rubber
very high

inherent

rs

ve

ca

Quality

ni

marked
less

lu

Tensile strength
Useful temperature range
Chemical resistance
Water absorption tendency
Resilience
Insulation property
Resistance to
organic solvents
9
...
Durability

it

200 kg/cm2
10°C-60°C
very poor
high
good

Low

2
...

4
...

6
...

8
...

low, depending on percentage
of sulphur
2000 kg/cm2
40°C to 100°C
higher
low
much better

much higher but swells

y
...
Elasticity

Vulcanized rubber

low
better
can be controlled by vulcanization

gi

Synthetic Rubbers

bl

Comparative study between natural and vulcanized rubber
Property

ht
tp
:/
/k
er
al
a

te

ch

no

lo

Synthetic rubber is artificially produced rubber-like polymers which can be stretched to
at least twice its length and on releasing the stress, it returns to its original shape and size
...
This variety is the most important synthetic rubber and it is obtained by copolymerization of butadiene and styrene
...
SBR is similar to natural rubber in processing character and also as finished
product
...
But
unfortunately it is easily attacked by oxidising agents, mainly ozone
...
It can be vulcanized as natural rubber
...
It is mainly used for the manufacture of tyres
...

(ii) GRA or Buna-N
...
blogspot
...
PM5

462

sp

462

n

...

bl

Properties
...
but due to the presence
of CN group, it is much more susceptible to alkali than natural rubber
...

Uses
...
It is used to manufacture parts for automobiles, aircraft
...

(iii) GR-M or Neoprene
...

Polymerize

nCH2 = C—CH—CH2 ¾¾¾¾® —CH2C = CH—CH2—

ni

Chloroprene

n

gi

ca

lu

Properties
...
It can be vulcanized by heating alone
...

Uses
...

lo

Reclaimed Rubber

ht
tp
:/
/k
er
al
a

te

ch

no

It is obtained from the waste rubber articles by the process of reclaimation
...
The waste rubber articles like tyres, tubes, footwares, gaskets etc
...
The unwanted ferrous materials are separated by electromagnetic
separator and then charged to an autoclave and digested with caustic soda solution at 200°C
under pressure for 8-15 hours
...
e
...

Sulphur is removed as sodium sulfide
...

Properties: Reclaimed rubber has inferior tensile strength, elasticity etc
...
It is cheaper and easier for fabrication
...
Reclaimed rubber is used for making tyres, tubes, belts, shoe soles, floor mats etc
...

Process
...
, antioxidants like amines and phosphites, fillers like
C-black, accelerators like benzothiazole, mercaptans, and coloring matters
...
Finally the material forms soft plastic mass
...

Vulcanization
• The process discovered by Charles Good Year in 1839 to improve the quality of
rubber by introducing sulfur at 100°C-140°C to the double bond of rubber
...
)

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH20-1
...
c
ot
y
...

og

ENGINEERING CHEMISTRY

it

Styrene rubber (GR-S)
Nitrile rubber (GR-A)

rs

Neoprene (GR-M)
Thiocol (GR-P)

ve

Hypalon
Polyurethane

lu

ni

Compounding of rubber
• Mixing of raw rubber with plasticizers, antioxidants, vulcanizing agents, fillers,
colours etc
...

ca

MISCELLANEOUS POLYMERS

lo

gi

1
...
It is obtained by joining two or more layers of solid materials with the
help of an adhesive
...

ch

no

(a) Plywood
...
5-10 mm thick) are bonded such that
grains of alternate layers are at right angles to each other (cross-laminate)
...
, are minimised and becomes more strong compared
to wood of equal thickness
...
Plywood is used for making railway coach, cabinets, false-ceilings and in other
house building purposes
...
Paper, cloth, asbestos fibre, glass, metal etc
...
The
finished laminated plastics are light but strong and impermeable to water, oil etc
...

Uses
...
They are
also used for decorative purposes on table tops and wall panellings etc
...
Two glass sheets are joined by a plastic sheet in between to form
laminated glass
...

Bullet proof or splinter proof laminated glass is obtained by curing the laminates in
an oven under heat and pressure
...

Conducting polymers are made by special powders and are classified as
(a) π-electrons conducting polymer
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH20-1
...
c
ot
og

sp

465

POLYMERS

bl

(b) Conducting element-filled polymer
...

it

y
...
A metal atom with poly dentate ligand, which is a charge transfer complex is bound to the polymer to make it conducting
...
The polymer is made conducting by exposing the surfaces to charge transfer agents in gas or in solution place
...
This type of polymer is made by blending a conventional polymer with a conducting polymer
...

lu

Uses
...

gi

ca

SHORT QUESTIONS AND ANSWERS

lo

Q
...
What is functionality of a monomer?
Ans
...

te

ch

no

Q
...
What is gel point?
Ans
...
During
condensation polymerization it gets transformed from viscous material to a gel and the
transformation is sudden
...
The cause of gelation is
the formation of an infinite network of polymer and at this phase the resin becomes tough and
less extensible
...
3
...
Ageing is the autooxidation of rubber with time due to the presence of double bond
and due to this rubber becomes hard
...
4
...

Ans
...
The shaping is done with raw
rubber along with suphur and other ingredients like accelerators, antioxidants, fillers etc
...
Vulcanized rubber is used in vehicle tyres, hose, conveyer belt, electrical insulation
...
5
...
Nylon 6 is an additional polymer whereas nylon 66 is a condensation polymer
...

Q
...
Differentiate between a homopolymer and copolymer?

Ans
...

Q
...
Differentiate between addition and condensation polymerization
...
Addition polymerization is a reaction that gives a polymer, which is an exact multiple
of the original monomers
...
blogspot
...
PM5

465

...

bl

Condensation polymerization takes place through different functional groups of
monomers with elimination of small molecules like H2O etc
...
8
...
Copolymerization is the point polymerization of two or more monomers, e
...
,
butadiene and styrene to yield GR-S rubber
...
9
...
Polymers are different from other small sized molecules as they are mixtures of
molecules having different molecular masses
...

Q
...
What is an elastomer?
Ans
...

Q
...
Why is the density of HDPE different from LDPE?
Ans
...
But for LDPE, due to its branched structure, packing efficiency
is low and hence density is low
...
12
...
In thermosetting plastics, the monomers are bound to each other by strong covalent
bonds, which cannot be broken on heating
...

Q
...
What is natural rubber and what is gutta-percha?
Ans
...

Q
...
Why is teflon highly chemical resistant?
Ans
...

Q
...
Why is PVC soft and flexible but bakelite is hard and brittle?
Ans
...
When the force becomes too large the
covalent bonds are broken and it becomes brittle
...
16
...
Natural rubber possesses many undesirable properties and so to improve its
properties it is usually compounded with different ingredients like plasticizers, antioxidants,
filler, colorant etc
...
17
...
Raw rubber has high elasticity, tackiness, poor chemical resistance, poor strength,
large water absorption capacity etc
...
e
...

Vulcanization, thus, improves all the above properties
...
18
...
Below the glass transition temperature, the polymer is brittle and above it, they
would deform but not break
...
blogspot
...
PM5

466

...
19
...

bl

Ans
...

Q
...
What are alkyd resins?

ve

rs

it

Ans
...
Phthalic anhydride is used
instead of an acid and alcohol is polyfunctional alcohol, glycerol
...

Q
...
What is polymethyl methacrylate (Trade name: Perspex)?
Ans
...
blogspot
...
PM5

467

sp

467

POLYMERS

...

bl

Polymer is:

EXERCISES

ch

no

lo

gi

ca

lu

ni

ve

rs

Properties and uses
It is a glass-like plastic
...
and also for
making binoculars, camera lenses, table lamp shades
...

Q
...
What is polyvinyl (Trade name: Fevicol) alcohol?
Ans
...
It is used as an adhesive
...
23
...
Biodegradation is a process by which refuse mixes with environment by
microorganisms
...

Development of biodegradable polymer biopol is now a challenge to scientists
...

Write short notes on (i) free radical polymerization (ii) cationic polymerization (iii) silicone resin
...

Discuss various methods of plastic processing
...

(a) Write short notes on

ht
tp
:/
/k
er
al
a

te

1
...

(b) Write the structures, two properties and uses of:
(i) PE, (ii) PP, (iii) PVC, (iv) PTFE, (v) Nylon 66
...

Write the structures of five addition polymers and five condensation polymers, with their respective monomers
...

Explain with example: (i) addition polymerization, (ii) co-polymerization, (iii) vulcanization of
rubber
...

Write short notes on:

7
...

(i) Rayon

(ii) Synthetic rubber

(iii) Types of plastics
...

(ii) Neoprene rubber

(iii) SBR

(iv) Silicone rubber
...

(b) Define the term functionality of monomers
...

(c) Discuss the preparation of bakelite and PVC plastic
...

sp

468

Discuss briefly the application of plastic in engineering and industry
...
blogspot
...
PM5

468

...
(a) Define the terms
(ii) Co-polymerization
...

(b) What is the effect of polymer structure on the strength and crystalline nature of polymer?

y
...

it

(d) What are silicones? Draw the polymer obtained by hydrolysing dichlorodimethyl silicone and
give its use
...
(a) Explain the terms with example
(i) addition polymerization

ve

(ii) co-polymerization
(iii) condensation polymerization
...

(c) How are the following produced: (i) Buna S (ii) thiokols? Mention their properties and uses
...
(a) What do you understand by vulcanization of rubber? What are the advantages and disadvantages? Give the structural unit of vulcanised rubber
...

13
...

(b) Give the manufacture and uses of
(i) teflon (ii) nylon 66
...
Give the
structure of bakelite
...
(a) Outline the general method of preparation of urethanes and state their applications
...

(c) Write note on glass reinforce plastic
...
Define the term crystallinity of polymer
...
List the difference between addition and condensation polymerization
...
Describe with a neat sketch the process of compression moulding
...
(a) Discuss the mechanism of addition polymerization
...

(c) Write note on silicone
...
(a) Discuss the preparation of natural rubber
...

(c) Describe the methods of preparation of neoprene and silicone rubber
...

20
...

21
...
Write preparation, properties and uses of
(i) Phenol-formaldehyde resin, (ii) Silicone rubber (iii) Polyethylene
...
Distinguish between the following with examples:
(i) Natural and synthetic rubber
(ii) Addition and condensation polymerization
(iii) Thermo plastic and thermosetting plastic
...
blogspot
...
PM5

469

sp

469

POLYMERS

...
Write short notes on
(i) Teflon (ii) Cellulose acetate (iii) Silicone (iv) SBR
...
(a) Define and give examples for

y
...

bl

og

ENGINEERING CHEMISTRY

it

(b) Explain how the polymers are classified on the basis of their thermal behaviour and method
of polymerization
...

26
...

32
...

te

ch

33
...

(a) Write short notes on preparation, properties and uses of (i) bakelite, (ii) epoxy resin
...
Give its structure, properties and uses
...

Write short notes on
(i) Polypropylene
(ii) Plexi glass
...

(a) What are bakelite and PTFE? Name any four commercial thermoplastics
...

(b) ExplainVulcanization of rubber
...

(d) Explain the chemical resistant and thermal resistant polymers
...

Write a note on reclaimed rubber
...

(b) Write short notes on (i) Plastic deformation, (ii) Moulding techniques
...

Give a brief account of
(i) Vulcanization of rubber, (ii) Compounding of rubber
...

(a) How is natural rubber obtained from latex?
(b) Explain compounding and vulcanization of rubber
...

How do the properties of polymer change with Zeigler-Natta polymerization?
(a) Mention the technical tests of polymers
...

What is biodegradation of polymers?

no

29
...

ni

28
...

27
...

35
...

37
...

39
...

41
...

43
...

45
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH20-1
...
c
ot
sp
og
bl

Paints

ve

rs

it

y
...

ca

A paint is a product formulated to protect and decorate mainly metallic and wooden
surfaces
...

gi

• Pigments, which scatter and absorb light, so that the paint covers up the surface
underneath and decorates it with colour
...

ch

In gloss paints the film forming polymers are alkyd resins; in emulsion paints they are
latex polymers
...

In gloss paints a vehicle is traditionally a hydrocarbon solvent
...

ht
tp
:/
/k
er
al
a

In case of synthetic resins a drying oil (linseed oil, tung oil, rapeseed oil, mustard oil)
may be used
...
The oil contains a long unsaturated
fatty acid chain
...
The film forming substances are
known as binders
...
The binder and the solvent are collectively
called a vehicle
...
They not only reduce the cost of
paint but also extends its durability
...

• It should be opaque
...

471

http://keralatechnologicaluniversity
...
com

...

bl

• It should be non-toxic
...

Characteristics of an ideal paint
• It should be chemically inert
...

rs

• It should be non-toxic
...

ve

Special types of paints

ni

(i) Fire resistant paints
(ii) Chemical resistant paints

lu

(iii) Luminous paints
...

gi

(vi) Metal paints
...

Importance of emulsion paints (Latex paints)

lo

(i) It can be employed on both interior and exterior surfaces
...

(iii) It does not have any disagreeable product
...

PVC (Pigment Volume Concentration)

te

PVC is defined as :

Volume of pigment in paint
Volume of pigment in the paint + volume of non-volatile vehicle in the paint

ht
tp
:/
/k
er
al
a
PVC =

The concept of PVC is very much important in case of paints as PVC controlsgloss,
rheological properties, washabilities and durability of a paint
...
e
...
1: Range of PVC in a given paint
Name

(i) Flat paints

(ii) Semi gloss paints

%PVC
5075
35-45

(iii) Gloss paints

25-35

(iv) Exterior house paints

28-36

(v) Metal primers

25-40

(vi) Wood primers

35-40

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH21-1
...
c
ot
og

Oils and/or Resins (Film forming
materials protect the surface
from weathering), Driers (accelerate the drying of film)

Linseed oil, Tung oil,
Dehydrated castor oil,
Fish oils, casein, Acrylics
...

y
...

Example

Aliphatics

ca

Aromatics
Inorganic
or Organic

Methyl ethyl ketone
(MEK)
...

Naphtha and other
petroleum fractions
...

(i) Opaque

gi

Pigments

ni

Esters

lu

(ii) Volatile i
...
,
low boiling
solvent based (thinners)

ve

rs

Vehicle

Types and Functions

it

Class

bl

Table 21
...

(iii) Special purpose

White extender pigments
BaCO3
...

Diatomaceous earth etc
...

no

lo

(ii) Transparent

te

ch

Extenders
or Inerts

ht
tp
:/
/k
er
al
a

Manufacturing of paints

The manufacture of paints involves only (i) mixing of the ingredients (ii) proper grinding
and lastly (iii) packing
...
21
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH21-1
...
c
ot
og

ENGINEERING CHEMISTRY

1
...
Red
nium
lead
dioxide

1
...
Chrommarine
oxide

Yellow

Black

1
...
Carbon
black

rs

3
...
Furnace
chromate
black

2
...
Iron
blues

2
...
Aluminium
powder

lu

4
...
Basic
1
...
Copper
chromate
plumber
powder

2
...
Cobalt 2
...
Lead
2
...
Lithopone

Brown

ve

2
...

Blue

it

Red

bl

Common pigments and their colours
White

ca

Emulsion paints

gi

Emulsion paints are those paints in which water is used in place of organic solvents as
thinner
...
:
• Water and

lo

• The vehicle of film forming material (a synthetic resin or latex)
...

Pigments and extenders are dispersed in such an emulsion
...

Advantages of an emulsion paint

te

• Emulsion paints can be applied on the surface of metal or wood very easily
...

• More durable and more impermeable to dust and dirt
...

• The surface on which the emulsion paint is applied can be easily washed with water
...

Constituents of emulsion paints
Resin

Stabiliser

Polyvinyl acetate

Methyl cellulose

Thymol

Polystyrene

Dextrin

Chlorothymol

Alkyd

Casein

Mercuric chloride

Preservative

Antifoaming agent
Pine oil, Kerosene

Starch alginates

Manufacture of an emulsion paint
Manufacture of emulsion paints involves following three steps:
• Protein dispersion
• Pigment dispersion
• Paint formation and addition of other ingredients
...
blogspot
...
PM5

474

sp

474

...
8
1
...
5
764
17
...
2
13
...

Constituents

bl

A typical composition of an emulsion paint

ni

Copolymer latex

466

lu

Distempers

ca

Distempers are water paints comprising pigments, extenders, binders, and water as a
dispersing medium
...

no

Cement paints

ch

Cement paint contains:
(i) White cement,

te

(ii) Colouring or pigments,
(iii) Hydrated limes, and

ht
tp
:/
/k
er
al
a

(iv) Fine sands as inert filler
...
In case of brick structure the dispersion medium
is water
...
Before applying
cement paint a primer coat of a dilute solution of sodium silicate and zinc sulphate is necessary
...

Varnishes

Varnishes are organic compounds used as protective coating similar to paints
...
e
...

Varnishes are classified under two heads:
• Oleoresinous varnishes and
• Spirit varnishes
...
While the spirit varnishes are solutions of resins in
volatile solvents only, generally methanol and ethanol
...

Oleoresinous varnishes are also classified as:
(i) long oil varnishes have high proportions of drying oil
(ii) short oil type contains a lower proportion of drying oil

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH21-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

476

(i) Short

Properties

6-15 gallon

(ii) Medium

Faster drying, harder
and more brittle film

20-30 gallon

General purposes

More weather resistant
pliable films

ve

35-60 gallon

Floor and furniture

Sparvarnishes

ni

(iii) Long

Field of
application

it

Drying oil
per 100 lb resins

rs

Type

y
...

The classification is based on the use of drying oil in gallons per 100 lb of resin
...
The sequences
are as follows:
• In case of natural resin, when the resin is insoluble in oil, the resin is depolymerised
first by heating it upto 350°C till foaming ceases
...
The mixture is cooled to 200°C and
thinner and drier are added
...
In either case filtration is necessary
...

The table given below furnishes the constituents of a varnish (i
...
, four main ingredients
of a varnish):
Film forming
materials, i
...
,
ingredient 1

Solvents and thinners,
i
...
, ingredient 2

(i) Oil: Linseed oil,
tung oil, cotton
seed oil, coconut
oil, saya oil etc
...

Driers, i
...
,
ingredient 3
Co, Mn, Pb, Zn
resinates, octotes etc
...
e
...

(ii) Natural resins:
Shellac, Rosin,
Kauri, Copal etc
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH21-1
...
c
ot
og

sp

477

PAINTS

Lacquers

Materials

1
...

bl

Lacquers are dispersion or solution of a film forming material (like-nitrocellulose), resins
and plasticizers in solvents and or diluents
...
The lacquer dries from the surface on which it is applied by simple
evaporation of the volatile constituents, i
...
, solvents
...
Pigments
(Not added in
clear lacquers)

gi

(i) Phenol aldehyde
(ii) Alkyd

(i) Esters:
(i) Ethyl acetate

no

3
...
Diluents

5
...
Japans are closely related to
enamels
...

Enamels are brushed or sprayed on the surface and finally hardened by baking
...
blogspot
...
PM5

477

...

bl

litharge at 230°C for 5 hrs
...
This lead oil is mixed with kerosene
(thinner) and asphaltum
...

A comparative study of paints, varnishes, lacquers and enamels is given below:
Varnish

Lacquer

Enamel

1
...
e
...
Used for protective
and decorative aspect

Same

Same

Same

3
...
1
...
The functions are

(i) To protect the film by reflecting back the destructive UV light

ht
tp
:/
/k
er
al
a

(ii) To strengthen the film

(iii) To impart an aesthetic appeal
Q
...
Name the main constituents of an oil varnish
...
(i) Synthetic resins

(ii) Drying oil

(iii) Volatile solvents
Q
...
What is a tonner?
Ans
...

Q
...
How are the paint films formed?
Ans
...

Q
...
What is drying of an oil?

Ans
...
e
...
A drying oil is generally
glyceride of unsaturated fatty acids
...
Otherwise, drying is a chemical
change of an oil accompanied by oxidation and polymerisation due to the presence of
unsaturation in the fatty acid portion of the formula of drying oil to form a protective film over
the surface
...
blogspot
...
PM5

478

...
6
...

bl

Ans
...

it

Q
...
What is a vehicle?

Q
...
Why are plasticisers added to a paint?

ni

Ans
...

ve

rs

Ans
...
The vehicles
may be film forming oil and other liquids, for example, turpentine, naphtha etc
...

Q
...
Name some common extenders used is paints
...
(i) China Clay
(ii) Gypsum

ca

(iii) Mica

gi

(iv) Silica
Q
...
What is enamel?

lo

(v) Talc
...
Enamel is a pigmented varnish
...
11
...
(i) By brushing
(ii) By dipping

te

(iii) By spraying

ht
tp
:/
/k
er
al
a

Q
...
Cite an example of a common spirit varnish
...
It is a solution of shellac, which is a naturally occurring resin, in methylated spirit
...
13
...

Ans
...

Q
...
What are the characteristics of an emulsion paint?
Ans
...

They can be employed on both interior or exterior surfaces
...
15
...
This is an emulsion paint
...
The monomer is generally ester
of acrylic or methacrylic acid
...
blogspot
...
PM5

479

sp

479

PAINTS

...

acrylic ester

Conc
...
CN → CH2 = C  CONH 2

CH 3

ni

ve

CH2 = C  COOR

CH3

methylacrylate

Ans
...
16
...

(i) Hiding

no

(v) Gloss etc
...
17
...
In the case of small articles, paint is applied by tumbling technique
...
This heating is known
as baking
...
, to paints
...
18
...
In the case of emulsion paints, the film-forming materials are various latexes
whereas in ordinary paints, the film-forming materials are drying oils
...

EXERCISES

1
...

Mention the constituents of a paint and explain their functions
...

Give the characteristics of a good paint
...

Write a short note on spirit varnish
...

Distinguish between paint and varnish
...

Write a short note on emulsion paint
...

What are lacquers?

8
...
blogspot
...
PM5

480

sp

480

...

it
rs

22

ni

ve

Solid State Chemistry

gi

ca

lu

Solids are mainly characterised by their definite shapes and considerable mechanical strength
and rigidity
...
) of the solid
...
The forces of attraction between these units are large
enough
...

In a crystalline solid, the constituent atoms are arranged in a definite pattern constantly
repeated and in consequence giving rise to a definite geometrical configuration of crystalline
solids
...
On
the other hand the amorphous solids have no definite geometrical shape
...

ht
tp
:/
/k
er
al
a

The term crystal originates from the Greek word Krystallos that means clear ice, and
was first applied to transparent quartz stone with a wrong assumption that these stones were
formed from water by extreme cold
...

A crystal grows from melt or a solution or from gaseous state by the deposition of atoms
or ions onto its surfaces by which crystals are bounded
...
The angle between the normals to the two
intersecting faces is called the interfacial angle
...
There is a basic unit in any real crystal and when the basic unit is
systematically repeated, reproduces the whole structure
...

The various modes of arrangement of atoms of molecules in space to satisfy the need of
periodicity are governed by some specific rules and principles which lead to the development
of the subject of crystallography
...

481

http://keralatechnologicaluniversity
...
com

...

bl

Geometrical crystallography is concerned with the outward spatial arrangement of crystal
planes and the geometrical shapes of the crystals and thus crystallography is dependent upon
the three following fundamental laws
...

ve

Law of constancy of interfacial angle or Stenos law

lo

gi

ca

lu

ni

The law states that the angles between the corresponding faces on various
crystals of the same substance are constant
...
These faces always intersect at an angle, called interfacial
angle
...

It is often seen that the crystal faces are unequally
developed, leading to various shapes of the crystals
...
In Fig
...
1,
two crystals are represented two-dimensionally
...

For example, NaCl crystallises as cubes from aqueous
solution and as octahedral from urea solution but interfacial
angles of all crystals of NaCl are found to be 90°
...
22
...

ch

Law of rational indices

Z

ht
tp
:/
/k
er
al
a

te

In 1784 Haüy proposed the law of rational
indices or rational intercepts
...
For describing the
geometry of a crystal usually three non-co-planar
co-ordinate axes are selected arbitrarily
...
According to this law, the
ratio between intercepts on crystallographic
axes for the different faces of a crystal can
always be represented by rational numbers
...

To illustrate, let us consider a plane ABC in
the crystal as shown below:

C

N
c
a
L

X

b

O

M
B

Y

A

Fig
...
2 Intercepts of crystallographic
planes
...
These intercepts are in the ratio of 2a : 3b : 4c, where 2, 3 and 4 are simple
integral whole numbers and the standard intercepts are a, b and c
...
These ratios characterise and represent any plane of the
crystal
...
If any plane is parallel
to one axis, then it will cut it at infinity
...
The Miller indices of a
plane are obtained by taking the reciprocals of the coefficients of a, b, and c i
...
, Weiss indices

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH22-1
...
c
ot
og

sp

483

SOLID STATE CHEMISTRY

y
...
Thus, the
1
1
Miller indices of the plane (2a : b : 2c) will be : 1 : i
...
, 1 : 2 : 1 and this plane or face is
2
2
indicated as (1 2 1) face of the crystal
...
e
...

If a plane produces an intercept on the negative side, say a : b : ∞ c, the Miller indices

ve

and

it

Now, for a plane perpendicular to one axis and parallel to the other two, having intercepts
a : ∞ b : ∞ c will have indices, as:
Weiss indices 1 : ∞ : ∞

for the plane would be (1 1 0), the bar above one indicates the intersection of the plane on the

ni

negative side of the axis
...

ca

lu

Thus, if a face of a crystal makes intercepts OA, OB and OC on the three axes, then the
lengths of the intercepts may be expressed as OA/a, OB/b and OC/c where, a, b and c are unit
distances along three axes
...
e
...

The distance between the parallel planes in a crystal is designated as dhkl
...

Some of the Miller indices in the case of cubic lattices are shown in Fig
...
3 below
...
22
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH22-1
...
c
ot
og

ENGINEERING CHEMISTRY

The law of symmetry

rs

it

y
...
Symmetry in crystals may be
with respect to : a plane, a line or a point
...
There are three types of
symmetry elements associated with a crystal, namely:
• plane of symmetry
• line of symmetry, and
• centre of symmetry
...

Line of symmetry

gi

ca

lu

A crystal is said to possess a line of symmetry if it is possible to draw an imaginary line
through the centre of the crystal and then to revolve the crystal about this line through 360° in
such a way that the crystal appears unchanged more than once
...
If similar view appears two, three, four or six times during one complete revolution
of 360°, the crystal is said to possess two, three, four or six fold axes of symmetry
...
A crystal can have only one centre of symmetry
...
The cube has the greatest symmetry elements:
(i) Nine plane of symmetries
(ii) Thirteen axes of symmetries
(iii) One centre of symmetry i
...
, altogether twenty-three elements of symmetry
...
22
...

(a) planes of symmetry; (b) axes of symmetry; (c) centres of symmetry
...
blogspot
...
PM5

sp

484

484

...

bl

The idea of lattice developed from the internal regularity suggested from the external
appearance of the crystal
...
Thus a lattice may be defined as an
infinite set of points repeated regularly through space
...
When a set of points occur regularly in a plane, it constitutes a two dimensional
lattice
...

ca

(a)

lu

a

gi

b

ch

no

lo

b

a

a
(c)

ht
tp
:/
/k
er
al
a

te

(b)

(d)

Fig
...
5 Lattice arrangement: (a) one dimensional;
(b, c) two dimensional; (d) three dimensional or space lattice
...
1
...
blogspot
...
PM5

485

...
of
space lattices

Examples

y
...
1 Crystal systems and their characteristics
System

a=b=c

α = β = γ = 90°

3

NaCl, KCl, CsCl, ZnS

2
...
Orthorhombic

a≠b≠c

α = β = γ = 90°

4

KNO3, K2SO4, BaSO4,
AgBr

4
...
Triclinic

a≠b≠c

α ≠ β ≠ γ ≠ 90°

1

6
...
Trigonal
or
Rhombohedral

a=b=c

α = β = γ ≠ 90°

rs
ve

NaHCO3, Na2SO4
...
5H2O, K2Cr2O7,
H3PO3

no

c
c
90°

90°

ht
tp
:/
/k
er
al
a

90°

a
a
90°
a
Orthorhombic

a

Cubic

a°

90°

a

te

90°

90°

90°

ch

a

a

it

1
...
22
...

This classification is based on the magnitude of the unit cell length and the angle of
inclination between them
...
Thus the unit cell is the essential feature of the crystal structure
...
22
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH22-1
...
c
ot
Cubic (l)

Cubic (F)

lu

ni

ve

rs

Cubic (P)

it

y
...
22
...

CUBIC CRYSTALS
In a cubic crystal, the intercepts on the three axes are equal and all the angles are equal to 90°
...
blogspot
...
PM5

487

...

8

gi

ca

lu

ni

ve

rs

=

y
...
In simple crystal lattice, there are lattice points at the eight
corners of the unit cell
...
So the total contribution of all the eight corner atoms to each cell

(b)
Body centered
lattice

lo

(a)
Simple lattice

(c)
Face centered
lattice

ht
tp
:/
/k
er
al
a

te

ch

no

Fig
...
8 Bravais lattices of a cubic system
...
22
...

(ii) Body Centered Crystal Lattice
...
A BC cell has one additional atom at the centre besides having one atom each its right corners
...
Thus, the total number of atoms per
unit cell
= 1 (at the centre) + 8 × 1/8 (at the 8 corners)
= 1 + 1 = 2 atoms/unit cell of BCC

1/8
atom
1 atom

Fig
...
10 Unit cell of body centered cubic
...
blogspot
...
PM5

488

...

bl

(iii) Face Centered Crystal Lattice
...
An FCC has one atom at the centre of the each face besides having one atom at
each corner
...
Since there are six faces of a cube, so that total number of
atoms per unit cell
...
22
...

2

h + k2 + l 2

ch

where a = side of the cube
...

te

Atomic radius of a cubic lattice

ht
tp
:/
/k
er
al
a

Atomic radius of a unit cell may be defined as half the distance between the centres of
two immediate neighbours in a unit cell and is denoted by r
...

Thus, for a simple cubic (SC) cell
atomic radius r = a/2
as we know that a = 2r
2r

2r

a
1/8 atom

Fig
...
12 Simple cubic cell
...
blogspot
...
PM5

489

...
22
...

lu

or

ca

r = a/2 2

Thus

ni

While for face centered cubic cell (FCC)
(4r2) = a2 + a2
16r2 = 2a2

rs

a

a

it

4r

y
...
22
...

Radius ratio

Radius ratio is the ratio of the cation radius to that of the anion in an ionic solid
...

Radius of anion (r− )

Solid defects

Crystals are formed depending on perfectly regular arrangement of structural units
...
In case of most ionic crystals, the ions are not arranged
in a perfect order and these crystals are said to have defects or in other words this deviation
may be regarded as crystal imperfections
...

• Non-stoichiometric defects or impurity defects
...
There are certain crystals is which some of the lattice points
remain unoccupied i
...
, the crystals have vacancies
...
blogspot
...
PM5

490

...

bl

equal number of cationic and anionic vacancies would exist in the crystal lattice as
shown in Fig
...
15 below
...

Such defect is found in crystals of NaCl
...
Frenkel defects arise with those crystals in which an ion leaves
its normal lattice site and occupies an interstitial site in the same crystal
...

Schottky defect

Frenkel defect

lo

Non-stoichiometric defects

gi

Fig
...
15 Defects in crystals
...
These impurities in crystalline substance drastically change
their properties
...
1%) is added to
NaCl, the conductivity of NaCl increases by 10000 times
...

The insertion of Ca2+ ions for Na+ ions leads to create lattice vacancies and such vacancies
permit the migration of ions as a result of which the conductivity of impure crystal increases
...
Impurity defects are
introduced under controlled conditions in germanium and silicon in the production of
semiconductors
...
There is
an excess of either metal or non-metal atoms in non-stoichiometric compounds
...

Metal excess may occur in the following ways:
(a) an anion may be missing from its lattice site and an electron be present there for
maintaining charge balance
...

(b) an extra metal atom may be present in an interstitial lattice site and an electron
being present in some other interstitial position balances the charge
...
The free electron present is
responsible for excitation to higher energy level by absorption of radiation of particular
wavelengths
...

Metal deficiency may also occur as follows:
A positive ion may be missing from its lattice position and a doubly charged cation
maintains the charge balance
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH22-1
...
c
ot
og

ENGINEERING CHEMISTRY

Role of Silicon (Si) and Germenium (Ge) in the field of semiconductors

no

lo

gi

ca

lu

ni

ve

rs

it

y
...
Semiconductors are defined as inorganic crystals responding
to electronegativity when excited by heat or electromagnetic radiation
...
However, impurity doped Si and Ge exhibit semiconductivity
...
Both in Si and Ge, each atom is covalently bonded to four neighbours
such that all four outer electrons of each are involved in bonding
...

Similarly, if a group III element like B, Al etc, is introduced in place of Ge or Si, an electron
vacancy in covalently bonded structure will be generated and such type of electron vacancy is
known as hole
...
So, electrons are able to move in a crystal
having such electron vacancies or hole and thus the crystal exhibits electrical conductivity
...
In other cases, there are some semiconductors
in which electrical conductivity is imposed due to presence of positive holes, they are known as
p-type semiconductors, discussed later on
...

te

ch

Highlight:
It may be noted that both type of semiconductors (n- and p-type) are electrically
neutral
...
A triod transistor
contains two P-N junction diodes placed back to back
...

The following Fig
...
16(a) and (b) show a grown P-N-P junction triode transistor and
an N-P-N junction transistor respecttively
Emitter

(Input) E

P

Collector

Base

N

P

C (Output)

(Input) E

B (Base)
(a) A PNP transistor

N

P

N

B (Base)
(b) An NPN transistor

Fig
...
16 Transistors
...
blogspot
...
PM5

492

sp

492

C (Output)

...

bl

Function of the emitter is to inject majority charge carriers into the base, and a collector
is to collect these carriers through the base
...

In an NPN transistor electron moves
...
e
...

The alloy junction transistor is shown in the following figure (Fig
...
17)
...
22
...
Collector is larger in size than the emitter
...

• High melting and boiling points in most cases
...

• Metallic lustre
• Constancy
• Emission of electrons by some metals under the action of heat and light
...
Separate bonding schemes have been proposed for the metals to give an accurate
explanation of the characteristics of metal
...

Band theory

Band theory provides the most satisfactory explanation of the characteristics of the
metallic properties in a very natural manner
...
O
...
For homonuclear diatomic species, the
combination of two atomic orbitals gives rise to two molecular orbitals and these are two new
energy levels for the electrons in the two joint fields of the nuclei
...
blogspot
...
PM5

493

...

bl

aggregate of a large number of atoms (n), each offering one orbital for the combination with
others, so there will be a total of n new energy levels similar to n number of molecular orbitals
(M
...
s)
...
The valence electrons from all the atoms will enter every level and a metal thus
consists of energy bands formed by merging of individual atomic orbitals
...
The electronic configuration of a Li atom is 1s2, 2s1
...
Similarly
three or four Li atoms would give rise to formation of three or four energy levels by combination
of their 2s-atomic orbitals
...
Similar combination of the p-atomic
orbitals will form a 2p energy band containing 3n-energy levels
...
When the electrons gain thermal energy or are placed in an electric field
...
This phenomenon explains the high
thermal and electrical conductivities of metals
...
22
...
2s2
...
3s2
...
One finds that the 3p band (formed by unoccupied
3p atomic orbitals of the Mg atoms) overlaps the 3s band in Mg and there is no energy gap
between the highest occupied and lowest vacant electronic energy levels and Mg is an excellent
conductor
...
22
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH22-1
...
c
ot
og

sp

495

SOLID STATE CHEMISTRY

it

y
...
The energy distribution of these
electrons follows roughly the MaxwellBoltzmann law
...
This conclusion
is in harmony with the Dulongs and Petits law
...
e
...
It is these electrons which are
mostly affected when a number of atoms are brought very close together as during the formation
of a solid
...
It may be filled by electrons completely or partially
...

In fact, it may be defined as the lowest unfilled energy band
...
The gap between these two bands, namely valence band and conduction band, is
known as forbidden energy gap
...
22
...
An electron in the conduction band can jump more readily
to an adjacent conduction band than it can jump back to its original position
...
It may be noted that the covalent forces of the crystal lattice have their source in
the valence band
...
This hole can travel to an adjacent atom by
taking an electron from that atom, which involves the breaking an existing covalent bond and
then re-establishing a covalent bond by filling up the hole
...
This is shown in Fig
...
21 below
...
blogspot
...
PM5

495

...

E

Fig
...
21

lo

gi

ca

lu

ni

In another way it may be concluded that the conditions in the conduction band have
nothing to do with the hole flow
...
Although holes flow with ease, they experience more opposition
than electron flow in the conduction band
...

• Holes exist in and move in the valence band
...

no

Conductors, semiconductors and insulators

te

ch

The band theory of metals may be extended to other non-metallic solids as well
...
The electrons lying in the
lower energy bands, which are normally filled, play no part in the process of conduction
...

In terms of energy bands it means that electrical conductors are those which have
overlapping valence and conduction bands
...

0

E

Conduction
band
Overlap
Valence band

16

Fig
...
22

Another point to be mentioned is that here the forbidden gap is not present for good
conductors
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH22-1
...
c
ot
og

Semiconductors

ni

ve

rs

it

y
...
For example germanium (Ge) and silicon (Si)
...

The resistivity of the semiconductors ranges from 105 to 103 ohm-cm and decreases with
increase in temperature according to an exponential law
...
The semiconductors which conduct even in chemically
pure state are called intrinsic semiconductors
...
The energy gap is of the order of 1 eV
...
22
...
As temperature increases, the width of the forbidden gap decreases, so that some
of the electrons are liberated into the conduction band
...
Semiconductors are
of two types:
Ge atom

Ge
G
Ge

F
D

...

...

Ge

sp

497

SOLID STATE CHEMISTRY

Ge

Covalent bond

Fig
...
23 (a) Intrinsic Ge
...
22
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH22-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

498

it

y
...
In such semiconductors the energy gap between the valence band and conduction band is very small (Fig
...
23)
...
But their
electrical conductivity is raised with increase in temperature to break the covalent
bonds (Fig
...
23(a)) to get conducting electrons (Fig
...
23(b))
...
22
...
Thus a negative charge moves from G to A
...
e
...
An intrinsic semiconductor may be defined as one in which the number of conduction
electrons is equal to the number of holes
...
Semiconductor behaviour may also be imposed in certain substances by the deliberate addition of impurities
...
Example, n-type and p-type semiconductors (discussed earlier)
...

pentavalent atoms (As, Sb, P) or

l

trivalent atoms (Ga, In, P, B)
...
The trivalent atom, on the other hand, is called acceptor atom as
it accepts one electron from Ge atom
...

a

Depending on the type of doping agent, extrinsic semiconductors are divided into two
classes:
(i) N-type semiconductors

Ge

Ge

...

Ge

Hole

B

Ge

...

Ge

...

Sb

...

Ge

...

Ge

Ge

Fig
...
23 (c) N-type semiconductor
...
22
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH22-1
...
c
ot
Collector junction
N

P

Emitter

0
...

1 mA

bl

P

og

Emitter junction

Hole flow

Ve

Vc

rs

0
...
22
...

N

P

Emitter

Electron flow

(a)

Vc

lo

0
...
99 mA

ca

1 mA

Base
(b)

no

Fig
...
23 (f) Working of an NPN transistor
...
Emitter arrow shows the direction of flow of conventional current
...

Insulators

Insulators are those materials in which valence electrons are bound very tightly to their
parent atoms and thus require a very large electrical field to remove them from the attraction
of the nuclei
...
22
...

0
Empty conduction
band

E

Large energy
or forbidden gap
Valence band
16

Fig
...
24

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH22-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

500

y
...
Increase in temperature causes some
electrons to move to the conduction band, which accounts for the negative resistance
temperature coefficient of insulators
...
This phenomenon is known as thermionic emission
...
The current obtained by flow of
thermions is called thermionic current
...
A triode has three elctrodes
...

no

lo

gi

Filament

Fig
...
25 Directly heated cathode
...
A
diode acts as a perfect rectifier
...
22
...

A
Input A
...

F

R

Output
D
...

Fig
...
26 Rectifier
...

When light is incident on such a combination, an internal voltage is generated which causes
the current to flow through internal circuit, here no external battery is needed
...
m
...

generated is proportional to the radiant energy received in solar batteries
...
blogspot
...
PM5

500

...

A
Barrier layer

Electron
flow

Iron Base

rs

it

Selenium

Fig
...
27 Photovoltaic cell
...
In the iron-selenium cell, selenium layer is placed on an iron disc and then extremely
thin transparent film of gold or silver is formed on the selenium to act as front electrode
...
A
contact ring on the silver layer acts as one electrode and the iron base as the other
...
e
...
22
...
The flow in
the opposite direction is not permitted by the barrier layer because it acts as a rectifier
...
m
...
generated internally between silver electrode and selenium is directly proportional to
the incident flux
...
e
...

l

The internal e
...
f
...

Such cells are used

te

ch

l

l

ht
tp
:/
/k
er
al
a

(a) in devices like portable exposure meters,
(b) in direct reading illumination meters and with low resistance relays for on and off
operations and
(c) in other monitoring operations in industries
...
Calculate the Miller indices of crystal planes whose Weiss indices are :

(a) a/2, 2b/3, ∞ c;
Solution:

(b) 2a/3, 2b, c/3
...
blogspot
...
PM5

501

sp

501

SOLID STATE CHEMISTRY

...

450

pm
8
= 159 pm
...

a

d220 =

it

Solution
...
Determine the interplanar spacing between the (220) planes of a cubic lattice
of length 450 pm
...
8 Å, b = 9
...
2 Å
α = 41°,

(ii)

β = 83°,

γ = 93°

a = b = 10
...
Classify the following unit cells into proper system:

c = 14
...
(i) Here a ≠ b ≠ c i
...
, the three primitives are unequal
...
In other words, there is complete lack of symmetry, which is
characteristic of triclinic structure
...

lo

Therefore, this unit cell belongs to hexagonal crystal structure (see Table 22
...

no

Problem 4
...
Also calculate the
spacing between the 110 planes of NaCl crystal
...
167 g cm3)
nM
N
where, a = length of the edge, n = no
...
wt
...
We have,

ht
tp
:/
/k
er
al
a

Here, M = 58
...
023 × 1023 g mol1, n = 4, ρ = 2
...

∴

∴

a3ρ =

4 × 58
...
023 × 10 23

a = 5
...
65 Å
d=

a
2

2

h +k +l

2

=

5
...

(1 + 12 + 0 2 ) 1/ 2
2

Problem 5
...
Calculate
the voltage gain and comment on the voltage gain
...
Here current gain α =

collector current I c current in the output circuit
=
emitter current I e
current in the input circuit

= 0
...

If R of output circuit = 2000 ohm, then Resistance gain =

2000
= 100
20

[when R (input) = 20 Ω
...
96 × 100 = 96 V

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH22-1
...
c
ot
og

sp

503

SOLID STATE CHEMISTRY

Comment

it

y
...
If the output voltage is applied to a second
transistor it is increased still more
...

rs

EXERCISES

Distinguish between (a) crystalline solids and amorphous solids, (b) semiconductors and insulators
...

Explain: (a) plane of symmetry, (b) centre of symmetry, (c) axis of symmetry
...

Explain Band Theory
...

Explain the role of silicon and germanium in the field of semiconductors
...

Explain the termsamorphous and crystalline solids
...

How can electrical conductivity to metal be explained on the basis of bond theory?

7
...

What do you mean by solid defect? Describe (a) Frenkel defect and (b) Schottky defect
...

Define the laws of crystallography
...
Define transistors
...

11
...

no

12
...
What is the utility of doping agent in a semiconductor?

ch

14
...

15
...
What do you mean by a photovoltaic cell? Explain its working principle and uses
...
If density of NaCl is 2
...
83 Å)
...
Calculate the density of copper
...
61 Å unit
(Cu = 63
...
98 g cm3)
...
Show that for BCC and FCC crystals the lattice constants are given by
aBCC = 4 r
3
aFCC =

4r
2

where r is the atomic radius
...
blogspot
...
PM5

503

...

23

ni

ve

Chromatography

INTRODUCTION

ca

lu

Chromatography is considered as a group of techniques for the separation of the components
(compounds) of mixtures by their continuous distribution between two phases, one of which is
moving past the other
...

ch

no

• A liquid stationary phase and a liquid or gaseous mobile phase (partition chromatography, here the partition between the stationary and mobile phases is the main cause
for separation of the components, hence the name)
...

ht
tp
:/
/k
er
al
a

• An inert gel which acts as a molecular sieve, and a liquid mobile phase (gel chromatography)
...

Types of Chromatography
Type of chromatography

Adsorbate phase

Adsorbent phase

Gas-liquid

Gas

Liquid

Liquid-liquid

Liquid

Liquid

Gas-solid

Gas

Solid

Liquid-solid

Liquid

Solid

Column Chromatography
• Adsorption chromatography
The technique was originally developed by the Russian botanist T
...
Wett in 1906
...
blogspot
...
c
ot
og
y
...

| Sodium carbonate
|
T
R Calcium carbonate
| Calcium phosphate
|
S Magnesium carbonate
| Magnesium oxide
| Calcium hydroxide
|
T
R Activated magnesium silicate
| Activated alumina
| Activated charcoal
S
| Activated magnesia
| Activated silica
|
T

Adsorbate (mobile phase)

Esters
Acetonitrile
Chloroform
Alcohols
Water
Pyridine

lo

etc
...
)

Fig
...
1 A set-up for column chromatography
...
blogspot
...
PM5

505

bl

Table 23
...
c
ot
og

ENGINEERING CHEMISTRY

sp

506

it

y
...

• Colourless components may be detected visually if they fluoresce normally or under
UV light
...
For colourless compounds the eluate is collected as a large number of fractions,
each of small volume
...

• Very efficient method of separation of mixtures of components
...
Separation of leaf pigments of spinach leaves viz
...

lu

Paper Chromatography

ht
tp
:/
/k
er
al
a

te

ch

no

lo

gi

ca

Paper chromatography is a type of chromatography in which the stationary phase is
water in the fibres of paper and the mobile phase is another solvent
...

water and mobile solvent
...
As a result the mixture separates as the chemicals
move at different speeds
...

Partition constant (partition or distribution coefficient) is defined as: the ratio of two
concentrations in the two layers is a constant when a solid is shaken with two immiscible
liquids as an equilibrium is set up to which the equilibrium law applies
...

The movement of components on the paper depends on the amount and nature of
stationary phase compared with the amount of mobile phase in the same part of the paper and
also on the partition coefficient
...
The Rf value for the substance is a measure of this fraction
...

There are two types of paper chromatography:
• Ascending chromatography
• Descending chromatography
The origin of the name depends on the nature of solvent movement
...

• 2-5 µl volumes of solutions of sample and reference compounds at about 2 cm intervals
of the line
...
blogspot
...
PM5

506

...

bl

• The paper is folded perpendicular to the line drawn
...

• The tank is prepared by placing the mobile phase (about 1 cm depth of the tank) and
the lid is placed
...

• The folded paper is placed in the tank followed by placing the lid
...
e
...

• The paper is removed, dried and now comes the question of location of the component
...
If so, the analyst has to develop the paper or plate in case of tlc with a suitable locating
agent
...
05%) (iv) ninhydrin for amino acid etc
...

Advantages
• Rapid and reliable separation and identification
...

Disadvantages
• Large scale separation of components is not possible
...

Thin Layer Chromatography (tlc)

ht
tp
:/
/k
er
al
a

te

ch

Here the stationary phase is a thin layer of a solid, generally silica gel or alumina, on a
glass or plastic plate while the mobile phase is a solvent
...
The position of equilibrium varies from one substance
to another as the components of a mixture separate
...

• Only a very small sample is required
...
It can be used
quickly to check whether a chemical reaction is taking place as expected
...

Detection of the components
• Coloured compounds are easy to detect on a tlc plate
...
The iodine is absorbed by
the compound giving coloured spots
...

• Alternatively a tlc plate may be impregnated with a fluorescent chemical
...

Rf values are used to record the distances moved by component chemicals of a mixture
relative to the distance moved by the solvent
...
blogspot
...
PM5

507

...

bl

General method
• The size of the glass plate is 20 × 20, 20 × 10, or 20 × 5 cm
...

• The slurry is quickly poured to a spreader or applicator and is spread (thickness
0
...

• The slurry is allowed to set for 3-4 min
...

• The plate is transferred to a desiccator over silica gel
...

• Eluted with mobile phase in a chromatographic chamber
...

• Rf is measured to identify the components, e
...
, Rf for L-lysine is 0
...
36 and L-leucine is 0
...

High Performance Liquid Chromatography (hplc)

ch

no

lo

gi

ca

hplc is a sophisticated technique of liquid chromatography
...
The stationary phase consists of very small particles of a solid (silica gel)
packed into a long steel tube
...
A pump provides very high pressure (1-550
bar, 0
...
6-8000 p
...
i) to maintain a flow rate of mobile phase at the rate of
0
...
The material (15-25 µl) to be chromatographed is injected through a septum
into the centre of the packing material with the help of a syringe
...

One application of hplc is to study the fate of drugs administered in the body
...
In a modern gasliquid apparatus, the stationary phase is a thin film of liquid adsorbed on the inside surface of
a coiled capillary tube of about 30 m long inside an oven
...
The mobile phase is a gas, which carries the vapours
of the sample mixture through column
...
The components are detected as they come out and the signal detector is
fed to a chart recorder
...
This time is called retention time (tr)
...
23
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH23-1
...
c
ot
og

sp

509

CHROMATOGRAPHY

bl

The areas under the peaks on the print out give a measure of the proportions of the
components of the mixture
...

A glc machine can be calibrated by injection of known amount of compounds and recording
their retention times
...

(ii) Measuring the level of alcohol in urine and blood samples
...

ni

Gas Chromatography (gc)

lu

The separation of the components in a mixture in the gaseous state achieved by partition
column chromatography using a gaseous mobile phase was first suggested by Martin and Synge
in 1941
...
During
the passage of the vapour of the sample through the column, separation of the components of
the mixture takes place by adsorption effects if the prepared column is of adsorbent only
...
It is better to use the term support for the liquid
phase rather than adsorbent as adsorption effects are undesirable in partition columns
...

ht
tp
:/
/k
er
al
a

The basic apparatus for gc is shown diagrammatically
...
23
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH23-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

510

bl

Highlight:
• Nernsts isotherm:

y
...

rs

Cs = concentration of component in stationary phase (Adsorbent)

ve

Cm = concentration of component in mobile phase (Adsorbate)
Some parameters of gc

lu

ni

• Retention time
...
It is measured on the abscissa of the chromatogram
from the start to the maximum peak
...
It refers to the volume of the solvent that is required to extract a
component and bring it to the detector
...

ht
tp
:/
/k
er
al
a

te

Signal (Concentration)

ch

no

lo

• Chromatogram
...
The concentration component is found to be proportional to the signal
...

A

Start

0

1

2

Volume or time
of retention

Fig
...
4 Chromatogram
...

• Efficiency
...

• Resolution
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH23-1
...
c
ot
og
y
...

What is meant by Rf in chromatography?
What are the advantages and disadvantages of paper chromatography?
What is thin layer chromatography (tlc)?
Mention the advantages of tlc
...

What are:
(a) hplc
(b) glc
(c) gc?

bl

EXERCISES
1
...

3
...

5
...

7
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH23-1
...
c
ot
sp
og
bl

it

y
...

This spectrum is due to the excitation of atoms by thermal or electrical means
...
The life-time of electrons in this excited state is short and they return to
either a lower excited state or to the ground state
...

Fluorescent lights and colours obtained by heating salts of certain elements in a flame are very
common examples of emissions spectra
...
In these cases the excited states usually have appreciable life times and emission of
light starts after excitation has ceased
...

ht
tp
:/
/k
er
al
a

te

An absorption spectrum is obtained by placing the substance between the spectrometer
and some source of energy, usually it is an electromagnetic radiation which is applied
...
The regions of electromagnetic radiation of greatest
interests to the organic chemists are 200-400 mµ (ultraviolet), 400-800 mµ (visible), and 2-16 µ
(infrared)
...
The energy absorbed is given by
E = hν

where h is Plancks constant and ν is the frequency of incident light (in cycles per second, cps)
...

The wave number is also used in the description of spectra
...
e
...

1
λ
512

http://keralatechnologicaluniversity
...
com

...

bl

Interpretations of molecular spectra by the organic chemists are based largely on
empirical correlations with extensive compilations of data
...
Absorption of ultraviolet and
visible light is chiefly caused by electronic excitation; the spectrum provides limited information
about the structure of the molecule
...
On the other hand, the proton magnetic resonance (pmr) of a compound owing to
nuclear spin transitions can usually be completely interpreted, and it provides information
about the number, nature, and environment of all the protons in the molecule
...

lu

Visible Light and Electromagnetic Spectrum
10

10

10

3

X-rays

10

5

10

7

10

Microwaves

lo

Cosmic rays

–1

gi

–3

ca

Nanometers
10

10

11

Radiowaves

IR

te

ch

no

UV

9

ht
tp
:/
/k
er
al
a

Violet

370

Indigo

430

Blue

450

490

Orange

Yellow

Green

550

590

Red

600

750

Fig
...
1 Wavelengths of electromagnetic radiation
...
e
...
e
...
The transition of energy, due to the displacement of a valence electron accompanied by
the electronic excitation, is a change in εv and εr of the molecule
...

Some terms concerning UV
Chromophore: A moiety of a molecule which is responsible for selective absorption of
radiation in a given range of specially UV or visible region
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH24-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

514

Hypsochromic shift: It is a shift of λmax to lower wavelength
...

shift
...

it

Hyperchromic and hypochromic effects: These terms refer to an increase and
decrease in absorptivity of the molecule respectively
...
They occur due
to electronic transition of a molecule
...
They involve n π* transition
...
The band
at 279 mµ observed in the UV spectrum of acetone is an example of an R-band
...
1,3,5-hexatriene is an example of such a conjugated system
...
The λmax values
are between 230-270 mµ and εmax less than 2000
...
In the presence of K-bands the position of the B-band is shifted to larger
wavelengths
...

no

lo

(iv) E-bands: These are also known as ethylenic bands and are characteristic of the
aromatic systems as are the B-bands
...

ch

The presence of an auxochromic group shifts an E-band to a higher wavelength
...
The bands at 210 mµ with εmax of 6200 for
phenol is an example of E-band
...
24
...

Radiation source
...
A xenon arc or, a mercury
lamp provides a more intense radiation
...
UV is a plot of absorbance vs
...

Applications of UV in analytical chemistry
The working formula:

A=εbc
is derived from Lambert-Beers law, where A is the absorbance, E is molar extinction coefficient,
b is the path length in cm and c is molar concentration (mol l1)
...
blogspot
...
PM5

514

...

bl

standard solutions of known concentrations are determined from the spectrophotometer and a
calibration graph is constructed
...

rs

it

s*

p4*

p*

ve
ni

n

lu

E

p3*

ca

p

lo

C=C
p – p*
160-180 m

no

C–C
s – p*
vac UV
Alkane –140-50

gi

s

C=O
p – p* 180 mm
n – p* 275 mm
n – s* 150 mm
(Ketone)

p2
p1

C = C—C = C
p2 – p3*
217 mm

ch

Fig
...
3 Energy diagram for the electronic transitions
...
But there is little electronic
interaction between isolated chromophoric groups
...
The rules for calculation of λmax values of
such compounds are relatively very simple and is exemplified below:
Calculation of λmax values
• For α, β unsaturated ketones:
(i) In order to calculate the absorption (λmax) of an α, β unsaturated ketones a base
value of 215 mµ is assigned
...

(iii) For each β substituent 12 mµ are added to the base value
...

(v) If the carbon-carbon double bond and the carboxyl group are in a five-membered
ring 10 mµ subtracted from the calculated value and if only the carbon-carbon
double bond is in a five membered ring 5 mµ is added
...

The correlation of calculated values and experimental values is within a permissible

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH24-1
...
c
ot
og

ENGINEERING CHEMISTRY

Example 1
...

b

a

it

a, b-unsaturated ketone

Methyl-vinyl-ketone:

H

rs

CH3
C = C—C = O

ve

H

gi

CH3

ca

lu

ni

H
In this case, there is no α and β substituent
...
So, the calculated λmax value is 215 mµ
...

Example 2
...

te

Calculated λmax value = 225 mµ
...

ht
tp
:/
/k
er
al
a

Example 3
...

H O

H

H

H3C—HC = C—C—CH3 º CH3—C = C—C = O
b

a

CH3

Here, base value is 215 mµ
There is no α substituent + 0 mµ
For one β substituent + 12 mµ

Calculated λmax value = 227 mµ
...

Example 4
...

H

CH3 O

H

CH3

H3C—C = C——C—CH3 º CH3—C = C—C = O
b

a

CH3

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH24-1
...
c
ot
og

Here base value is 215 mµ

y
...

Calculated λmax value = 237 mµ
...

CH3

Here, base value is 215 mµ
...

ch

no

lo

Observed λmax value = 246 mµ
...

gi

ca

For one α substituent + 10 mµ
...

Example 5
...

ht
tp
:/
/k
er
al
a

Here, the base value is 215 mµ
There is no α-substituent + 0 mµ
For each β-substituent + 24 mµ
For each ring to which
the double bond is exocylic + 5 mµ

Calculated λmax value = 244 mµ
Observed λmax value = 246 mµ
...
5 mµ are added for each acylic alkyl
substituent
...
Absorptions of
non-polar compound such as unsaturated hydrocarbon are not changed with a change in solvent
...

Butadiene
H H


H2C = C C = CH2

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH24-1
...
c
ot
og

ENGINEERING CHEMISTRY

bl

Here, the base value is 217 mµ
So, calculated value of λmax is 217 mµ

y
...

lu

ni

ve

rs

it

Conjugated dienes in which the double bonds are contained within rings absorb somewhat differently
...
For each alkyl substituent group on the diene system or, for each ring to which a carboncarbon double bond is exocylic, 5 mµ are added to the calculated value
...

Heteroannular diene

ca

Homoannular diene

For cyclic conjugated dienes:

ch

no

lo

gi

Homoannular diene (I)

Calculated λmax

Here, the base value is 253 mµ

te

For 3-ring residules + 5 × 3 mµ

ht
tp
:/
/k
er
al
a

For one ring to which
the carbon-carbon double bond is exocylic + 5 mµ

Calculated: λmax value is 273 mµ
...

Example 2
...

Calculated: λmax value is 234 mµ

Observed: λmax value is 235 mµ
...
blogspot
...
PM5

518

sp

518

...

bl

Absorption of light in both the ultraviolet and visible regions of the electromagnetic
spectrum takes place when the energy of light matches that required to induce in the molecule
and electronic transition and its associated vibrational and rotational transitions subsequently
...

2
3

ca

4

gi

5

lo

Fig
...
4 Reduction of the intensity of light by reflection at cell faces (rays 1-2),
absorption (ray 4) and scattering by particles (ray 5)
...

It ⇒ intensity of the transmitted light
...

The transmittance (T) is:
It
100 I t
and % T is given by % T =
Io
Io

ht
tp
:/
/k
er
al
a

T=

In 1760 Lambert put forward the relation between It and Io for various thicknesses (b) of
the substance
...

The law is stated as follows:
The rate of decrease in intensity of light with thickness is proportional to the
intensity of the incident light
...
blogspot
...
PM5

519

sp

519

INSTRUMENTAL METHODS OF ANALYSIS

...
303
It
I0/It is called the absorbance (A)
...

or

bl

ln It = k1b ln I0 or ln

I0
= log10
It

FG 1 IJ = log
H TK

10

T = 2 log (% T)
...

it

or

ENGINEERING CHEMISTRY

ni

Beer in 1852 put forward another relationship which is between absorbance and
concentration which is mathematically expressed as:

k2 C
I0
=
2
...
It may be stated also as: the
absorbance is proportional to the concentration
...
303 and k2 / 2
...
The value of a as well as
its name depend on units of concentration
...
b
...

When the absorbance is measured for 1% (w/v) solution in a 1 cm cell, then the equation
takes the form
1%

A = A 1cm
...
c
...

Colorimetric analysis is also based on BeerLamberts law
...

Infrared Spectroscopy
When infrared light is passed through a sample of an organic compound, some of the
frequencies are transmitted through the sample without being absorbed
...

Molecular vibration
At ordinary temperatures organic molecules are in a constant state of vibration each
bond having its characteristic stretching and bending frequency and being capable of absorbing
light of that frequency
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH24-1
...
c
ot
bl

og

sp

521

INSTRUMENTAL METHODS OF ANALYSIS

Two balls joined by a spring

it

y
...

rs

Calculation of vibrational frequencies

I
JK

ni

F
GH

1
k
2
...

As an example, we can calculate the approximate frequency of CH stretching vibration
from the following data,
k = 500 Nm1 = 5 × 105 gm s2 ×

ch

no

= 5 × 105 gs2
1 N = 1 kg × m/sec2 = 1000 gm s2

1
m

te

mC = mass of C-atom = 20 × 1024 gm
mN = mass of H-atom = 1
...
6 × 10 −24 g ) / (20 + 1
...
3 × 1013 s1

ν 9
...
1 × 105 m1 = 3100 cm1
So, νmax
...
) is 3100 cm1
...
As for example,
Stretching : C = C > CC
1600 cm1
3100 cm1
<

C=O

>

1700 cm1

Stretching : CH > CC

12 × 1
13

Stretching :

Stretching : OH

1100 1300 cm1
>

3500 cm1

12 × 12
24

16 × 1
17

CO
CO
11001300 cm1

<

12 × 16
28

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH24-1
...
c
ot
og

ENGINEERING CHEMISTRY

Infrared spectroscopy

y
...
24
...

+

+

–

it

–

rs
Scissoring

Stretching vibration

Rocking

In plane
bending vibration

ve

Asymmetric

Wagging

ni

Symmetric

Twisting

Out of plane
bending vibration

lu

Fig
...
5 Modes of vibration of the atoms in a molecule
...

• The progress of organic reactions can be studied with IR spectrum
...

• Identity of two samples that have identical spectra, generally it occurs in Finger
print region which is 1430 = 910 cm1

te

ch

no

Examples of some stretching and bending vibrations in alkanes
ν max
CH
stretching

2950 and 2820 cm1
CH2
bending

1458 cm1
CCH3
bending

14581380 cm1

ht
tp
:/
/k
er
al
a

IR Spectrum for ether and alcohol:
Replacement of CH2 in alkane by O results in ether
...
e
...

Aldehyde and ketones: IR spectra show absorption HC = O (stretching) at 1740
20 cm1 (strong); for a cyclic ketone stretching vibration is at 17251700 cm1 (strong) (distinction
from CHO and

C = O); CH (stretching) in CHO group is at 28802625 cm1 (weak to

medium)(distinction from

C = O)
...

H

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH24-1
...
c
ot
og

sp

523

INSTRUMENTAL METHODS OF ANALYSIS

y
...
is hidden by CH str),
1706 cm1 for C = O str
...
) at 1460 cm1
...
These bands are characteristic of long chain n-alkyl compounds,
in the solid state
...

Esters: For CH3 C OCH2CH3


O
νmax are:
1742 cm1 (C = O str
...
in acetate)
1370 cm1 (CH def
...
in CH3 or, CH2)
1449 cm1 (CH def
...
in acylic anhydride are 1840-1800 (s) and 1780-1740 cm1 (s)
...
νmax for various str
...
of bonds in an anhydride are shown below with the
arrows
...
)

te

H H H

H H H

def
...
) (str
...
) (str
...

β-diketones:

H

H

H

H—C—C—C—C—C—H
H O H O H

[1725-700 cm–1 single stretching

with greater intensity (as there
are two carbonyl groups)
in IR spectrum]

H—C—C = C—C—C—H
H

H

H

Absorption at 1655 cm–1 (s)

for

C = C—C = O

C = O in enols
enols contain this grouping,

®¾

α, β unsaturated ketones contain grouping

O H

H OH

1685-1665 cm–1 (s)

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH24-1
...
c
ot
og

ENGINEERING CHEMISTRY

but the shift to 1655 cm1 that occurs in these compounds is attributed to Hbonding
1

ca

lu

ni

ve

rs

it

y
...
True alcoholic OH absorption band near 3700 cm in enols are absent, but
there is absorption band near 2700 cm1 (s) which is attributed to the OH group (s) indicates
strong absorption, (m) indicates medium absorption
...
If there is Hbonding, then the region is 3400 3100 cm1 (s) CN str
...
+ 200 1020 cm1 in aromatic amines (s), NH def 16501590 cm1 (s m) in
primary amines, NH def 1650 1550 cm1 (s)
...

Aromatic Compounds: Aromatic compounds produce a large number of absorption
bands in the IR region
...

ht
tp
:/
/k
er
al
a

te

ch

no

lo

gi

C—H ⇒ 3080 3030 cm1 (w) (str) and the bands for C = C (in plane vibration) are
1625 1600 cm1 (v), 1590 1575 cm1 (v) and 1525 1475 cm1 (v)
...
However, because of a great deal of
overlapping of the various bands in the region 1225970 cm1; this region is not very useful
...
and def
...

1, 2-disubstituted benzene:
def
...
) show
stretching at 2941 cm–1

1, 3-disubstituted benzene:
H
H

C

2941 cm–1 (def )

H
str
...
is at 1613, 15878 and 1490 cm1

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH24-1
...
c
ot
og
bl

1450 cm1 for CH def in CH3
772 and 654 cm1 (s) for 1, 3-disubstitution
1, 4-di-substituted benzene:

y
...
(stretching), def
...
24
...
1 mm cell)
...
24
...
1 mm cell)
...
blogspot
...
PM5

525

sp

525

INSTRUMENTAL METHODS OF ANALYSIS

700

15

...

100

it
rs

60
40

ve

Transmittance %

80

3000

2000

1500
cm

–1

1000

900

800

700

lu

0
4000

ni

20

1000

900

800

700
100

80

lo

80

60

no

60
40

40

ch

Transmittance (%)

–2

cm

1500

gi

2000

ca

Fig
...
8 IR spectrum of chloroform (ethanol-free) (0
...

4000 3000
100

20

te

20

ht
tp
:/
/k
er
al
a

0

3

4

0
5

6

7

8

9

10

11

12

13

14

15

Wavelength (Microns)

Fig
...
9 Di-n-butyl ether, liquid film
...
24
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH24-1
...
c
ot
og

sp

527

INSTRUMENTAL METHODS OF ANALYSIS

bl

Nuclear Magnetic Resonance (nmr) or Proton Magnetic Resonance (pmr)
spectroscopy

ni

ve

rs

it

y
...

The technique is used (i) to identify unknown compounds, (ii) to check for impurities and
(iii) to study the shapes of molecules
...
The term nuclear
interprets the technique that detects nuclei of atoms such as hydrogen-1 (proton)
...
The term resonance is the
absorption of energy in the form of radio waves with the frequency corresponding to the size of
energy jump as the nuclei flip from one alignment in a magnetic field to the other (Fig
...
11)
...
Now since a rotating charged sphere is always
associated with it a magnetic moment, then all the charged particles in a nucleus will make
that nucleus to behave like a tiny bar magnet, with its magnetic moment along the axis of
rotation of the nucleus
...
These numbers can attain the values 0,

, 1,

3
2

etc
...
The nuclear magnetic moment is denoted by the symbol µ
...
e
...
If
2 2
O16 have

,

both protons and neutrons are even numbered then I is 0
...
If the sum of protons and neutrons is even, I is 0 or, integral (1, 2, etc
...

ch

Several nuclei H1, F19, C13 have a spin number I of

1
2

and a uniform spherical charge distribution
...

ht
tp
:/
/k
er
al
a

te

If a magnetic nucleus is placed in a uniform magnetic field it is seen that the magnetic
dipole assumes only a discrete set of orientations
...
The
magnetic nucleus can attain any one of the possible orientations indicated by (2I + 1)
...
One with respect to the direction of the applied magnetic field and
the other is aligned against the direction of the applied field (Fig
...
11)
...
24
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH24-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

528

no

lo

gi

ca

lu

ni

ve

rs

it

y
...

For protons if a magnetic field 14000 Gauss is applied the frequency of such energy
remains in the radio frequency region (60 megacycles per second)
...
24
...
But because the nucleus is spinning, the effect is that its
rotational axis draws a circle perpendicular to the applied field
...
24
...
This motion of the nucleus is called Precession
...
24
...

Theory of nuclear resonance
A proton in a static external magnetic field may assume only two possible orientations
corresponding to the energies of ± µHo
...
It is possible to the induce
transitions between these two orientations
...

The precessional frequency of the spinning nucleus i
...
, nuclear magnet is exactly equal
to the frequency of electromagnetic radiation necessary to induce a transition from one nuclear
spin state to another
...
This change can be brought
about through the application of electromagnetic radiation whose magnetic vector component
is rotating in a plane perpendicular to the main magnetic field
...
blogspot
...
PM5

528

...

bl

rotating magnetic field and the frequency of the precessing nucleus become equal, they are said
to be in resonance, and the absorption or emission of energy by the spinning nucleus then occurs
...

The electromagnetic radiation is supplied by an oscillator with its magnetic field at
right angles to the applied field and since the position of absorption peak, that is, where
resonance occurs, depends on the frequency of the oscillator or the strength of the applied
magnetic field
...
In practice it is easier to
vary the magnetic field rather than the frequency, the result is the nmr spectra which is
usually a graph of signal intensity (ordinate) against the magnetic field (abscissa) expressed in
milligauss at a fixed frequency (Fig
...
17)
...
24
...

Shielding, Deshielding and Chemical Shift

ht
tp
:/
/k
er
al
a

It might be expected that the resonance frequency for a given magnetic field depends
only on the nature of atomic nucleus concerned
...
The applied
magnetic field causes electrons surrounding a nucleus to circulate in a plane perpendicular to
the applied field, and this generates electric current to produce a magnetic field in opposition
to the applied magnetic field (Fig
...
13)
...
The relationship between the two
is expressed as:
H = Ho(1 σ) σ is called the shielding or,
screening constant (which is nondimensional) and
has a positive value
...
e
...
In that
case the proton is said to be deshielded
...

Then at a given radiofrequency, all protons absorb at
Fig
...
14 Diamagnetic electronic
the same effective field strength, but they absorb at
circulation about a nucleus
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH24-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

530

y
...

gi

ca

lu

ni

ve

rs

it

Shielding causes a shift of the resonance frequency to higher values of the applied field
(Ho), that is , the shift is upfield
...
The magnitude of
this shift is called chemical shift
...
Tetramethylsilane
[TMS, (CH3)4Si] is particularly useful for proton magnetic resonance (pmr)
...
The pmr spectrum of this compound shows a single sharp line
which occurs at higher field than any other protons in most of the common organic compounds
...

lo

CH3
CH3—Si—CH3

ht
tp
:/
/k
er
al
a

te

ch

no

CH3
(TMS)

Fig
...
15 Shielding of an acetylenic proton in terms of paramagnetic effects
...
The resonance frequency of the
proton of the compound is dependent on the strength of the applied magnetic field
...
However, the magnetic field can
also be expressed as Hertz (Hz) or cycles per second (cps)
...
g
...
Therefore it is
desirable to repart chemical shifts in such units that are independent of the operating conditions
of the spectrophotometer
...

This is usually in the range 1-10 and is expressed in ppm
...
blogspot
...
PM5

530

...
5 ppm
...
5 ppm
...

δ=

it

It is now becoming common practice to express chemical shifts in τ (tau) values, defined by:

rs

τ = 10-δ
...
Most protons have positive τ
value i
...
, δ < 10
...
e
...

ni

Position of signals (chemical shifts)

ca

lu

The greater the shielding of nucleus the larger is τ value (the smaller is δ)
...
Thus electronegativity
τ(ppm)
CH3Br

7
...
98

CH3F

CH3C

7
...
70

5
...
12

CH3N

gi

7
...

te

Si is less electronegative than carbon, so the protons of CH3 groups in TMS are more
shielded than those in CCH3
...

This effect is called
diamagnetic
anisotropy
...
24
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH24-1
...
c
ot
bl

og

ENGINEERING CHEMISTRY

sp

532

H

it

y
...
24
...

ch

no

At a given radio frequency, all the protons will absorb at a same effective field strength,
but they also absorb at different applied field strengths
...
24
...

Absorption

ht
tp
:/
/k
er
al
a

te

Downfield

Lowfield

(a)

Upfield

(b)

Fig
...
18 (a) NMR spectrum for ethanol at low resolution, (b) a signal
...

• The positions of signals predict something about the electronic environment of each
kind of proton
...

• The splitting of the signals into several peaks indicates the environment of a proton
with respect to other nearby protons
...
blogspot
...
PM5

532

...

bl

A set of protons with the same environment are said to be equivalent
...

it

Judging the equivalent protons

ve

rs

Each proton in a molecule is in turn to be replaced by some other atom Z
...

te

ch

no

lo

gi

ca

lu

ni

Example
...

Cl

H

Cl

1

Cl

H

H

Z

Z

H

Cl

H

H

Cl

H

Cl

CH3
Cl

CH3

1, 2-dichloropropane

(a)

CH3

(b)

C1 are diastereomeric, magnetically non-equivalent and give separate nmr signals

Examples: The number of signals indicate the presence of the number of sets of
magnetically nonequivalent protons in the molecule of the compound
...

→

a

b

sp

533

INSTRUMENTAL METHODS OF ANALYSES

2 nmr signals
...
blogspot
...
PM5

533

...

4 nmr signals
...

bl

3 nmr signals
...

→

c

b

Ha

→
→

a

it

CH 3  CH 2  CH 2  Cl

og

ENGINEERING CHEMISTRY

cH

Hd

no

Cl

→

ch

bH

lo

CH3 a

Cl

4 nmr signals
...
24
...
8 + 2
...
8 = 15
...
e
...
24
...
03 H is the number of
15
...
Then number of a protons, b protons and c protons in the compound are:
aH = 1
...
8 = 9
...
9 × 1
...
03 × 3
...
914
c

CH3 a

c

CH3

i
...
,

b

C
c

c

CH3 a º C11H16

CH3 a
(I)

1,4-Methyl tertiary butylbenzene

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH24-2
...
c
ot
200

100

c 9H

og

300

0
c 90

bl

400

CH3

c

Integration

CH3

2
...
8

rs

b 3H

c 4H

2
8

8
...

a

— C—CH3

it

CH3—
b

9
1

10 r
0d

lu

Fig
...
19 NMR spectrum of 1, 4-methyl tertiary butylbenzene (Proton counting)
...
H), increased if the t
...
H happens to be aligned against the applied field for half of the molecules
...
The signal is split into two peaks a doublet with equal
peak intensities
...
blogspot
...
PM5

535

sp

535

INSTRUMENTAL METHODS OF ANALYSES

...

Ho Signal is 1:3:3:1 quartet

Examples:

ni

Upfield doublet (n + 1)
(n = 1)
CHBr2—CH2Br
(n = 2)
Downfield triplet (n + 1)

ve

Spin combinations
for adjacent —CH3

CH3—CHBr2
(n = 3)
Downfield quartet

lo

Compound (B)

gi

Upfield doublet
(n = 1)

ca

lu

Compound (A)

ht
tp
:/
/k
er
al
a

te

ch

no

Signal splitting is determined by the number of neighbouring protons (n)
...

Peak area reflects the number of absorbing protons and the multiplicity of splittings
reflects the number of neighbouring protons (Figs
...
19 and 24
...

We may expect to observe spin splitting only gives the non-equivalent neighbouring
protons
...
By
neighbouring protons we mean most commonly protons on adjacent carbons
...
24
...
The multiplicity of a given group by
the expression (n + 1), where n is the number of protons on adjacent atoms
...
blogspot
...
PM5

536

...

bl

Introduction: Mass spectrometry is an accurate instrumental technique for determination of relative atomic masses and relative molecular masses
...

it

Basic principles

(Organic molecule)

(Molecule ion)

ni

+

ve

rs

In the simplest mass spectrometer, an organic molecule is bombarded with electrons and
+
is converted to highly energetic positively charged ions (molecular ions or parent ions, M
...
The loss of an electron from a molecule leads
+
to a radical cation (M
...
+ 2e

+

...

or

(radical)

ca

( ion )

(Molecular ion)

lu

The molecule ion (M
...
Thus,
M

sp

537

INSTRUMENTAL METHODS OF ANALYSES

+

...
A mass spectrum
is a plot of relative abundance against the ratio mass to charge (the m/z value)
...
Doubly charged ions are occasionally formed, they are deflected much more than singly
charged ions of the same mass; and they appear in the mass spectrum at the same value as
singly charged ions of the half, since,
2m m
=
2z
z
Neutral particles produced in the fragmentation, whether uncharged molecules (m2) or

...

Instrumentation

There is a high vacuum inside a mass spectrometer to produce and study ionised atoms
and molecules including fragments of molecules
...
24
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH24-2
...
c
ot
og

ENGINEERING CHEMISTRY

it

Sample
vapour

y
...
of
sample into the instrument

ve
ni

Production of molecular
+
ions M
...

rs

Bombarding with a beam of
high energy electrons
Deflection of moving stream
of ions with a magnetic field
to focus ions with a particular
mass on the detector
...
24
...

The instrument needs calibration using a reference compound with a known structure
and molecular mass so that the computer can print a scale on the mass spectrum
...
This makes it possible to calculate the relative atomic mass for the element
(see Fig
...
22)
...
), which is the
relative mass (molecular weight) of the compound
...
blogspot
...
PM5

538

sp

538

...

bl

Nitrogen rule
...
An odd molecular weight compound requires
an odd number of nitrogen atoms
...

rs

it

Metastable ions
...

ni

ve

So mass spectrum is a fragmentation pattern
...

lu

A chemist who synthesises new compounds can study their fragmentation pattern in a
mass spectrometer and determine its structure with the help of other spectra like infrared
spectroscopy (i
...
) and nuclear magnetic resonance (n
...
r
...
First glc separates the components in an unknown
mixture, such as a sample of polluted water, then mass spectrometry (ms) detects and identifies
the components
...
) is the most intense in straight-chain compounds, the intensity
reduces with increased chain branching
...

• In branched chain hydrocarbons cleavage is preferred at the bond adjacent to the
branch; thus giving rise to tertiary (3°) carbocations as 3° is more stable than 2°,
which in turn is more stable than 1° carbocations
...

Examples
...

CH3 CH3

CH3 CH3
+

CH3—C——CH—CH2—CH3

CH3—C + CH—CH2—CH3

...

CH3

CH3
+

CH3—CH—CH2—CH2—CH3

CH3—C + CH2—CH2—CH3

...
peak is high for unsaturated or cyclic
systems present in the molecule
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH24-2
...
c
ot
og

ENGINEERING CHEMISTRY

sp

540

R

CH2—R

+

...

y
...
Most alkylbenzenes give the more stable tropolium ion (I) rather
than the Benzyl cation (II)
...

+

...

lo

gi

+

...

+ CH2 = CH2

m/z 54

no

• Compounds such as alcohols, mercaptans, amines, esters cleave at CC bond β to
the hetero atom
...

te

...

R +

...
+
C = X—H

(Resonance stabilisation)

ht
tp
:/
/k
er
al
a

Cleavage

SHORT QUESTIONS AND ANSWERS

Q
...
What is atomic spectroscopy?
Ans
...
In
this state the atom remains in its lowest energy state and this is the most stable state of the
atom
...
The valence electrons are promoted to some
higher permitted energy level by absorption of energy
...
e
...
After
about 104 sec
...
The energy is emitted or absorbed in the form of electromagnetic
waves of definite frequency i
...
, of definite wavelengths
...

Q
...
What is atomic absorption spectroscopy?
Ans
...
It is applicable both to qualitative and quantitative analyses
...
blogspot
...
PM5

540

...

· Combination of LambertBeers law given

ni

ve

rs

A = log10

where

100 × I
Io

y
...
3
...
Transmittance is the ratio of the intensity of light transmitted to the intensity of
incident light
...

1 cm

ca

lu

A = Absorbance, A 1% = Absorbance of 1% (w/v) solution for path length of 1 cm,
1 cm
b = thickness (cm),
c = concentration (g/100 ml)
A 1% × molecular wt
...

10
Q
...
Calculate the concentration of a substance A in an ethanolic solution of
which the absorbance in a 1 cm cell at its λmax 241 nm was found to be 0
...
The A
(1%, 1 cm) is 540 at 241 nm
...

1 cm

no

Ans
...
890 = 540 × 1 × c
∴
C = 0
...

Q
...
Calculate the concentration in µg ml1 of a solution of substance B (mol
...

204
...
1 (M) HCl, showing absorbance at its λmax 277 nm of 0
...

The molar absorptivity (ε) at 277 nm is 5432
...
Here the working formula is A = εbc
...
613 = 5432 × 4 × c
∴
c = 2
...
82 ×105 × 204
...
00576 gl1
= 5
...

Q
...
What is molecular spectroscopy?
Ans
...
+ Etrans
...
In general molecular spectroscopy is absorption spectroscopy
...
7
...
When a molecule, specially organic molecule, absorbs UV radiations the electrons
are excited to higher energy levels
...
blogspot
...
PM5

541

...

bl

The following electron transitions take place:
σ → σ* (antibonding), n → σ*, n π* (antibonding)
π → π*
These electronic transitions are responsible for UV absorption of a molecule
...
8
...

Ans
...

(b) Quantitative:
• Analysis of various samples (drugs, dyes etc
...
9
...

og

ENGINEERING CHEMISTRY

CH = CH2

Styrene

lo

Extended conjugation is maximum in case of styrene
...

ch

NH2

no

:

Q
...
Which of the following compounds will have greater λmax?
(i)

(ii)

+
–
NH3Cl
...
Compound (i) shows greater λmax value as the lone pair on N atom comes into
resonance with the benzene ring to extend the conjugation
...

Q
...
Which of the following compounds will have greater λmax?
O


Ans
...

Q
...
What are the principles of IR?
Ans
...

They may be compared with two balls (atoms) joined by spring (bond)
...
, as shown below
...

stretching

bending or
deformation

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH24-2
...
c
ot
og

sp

543

INSTRUMENTAL METHODS OF ANALYSES

rs

it

y
...
13
...
R
...

Ans
...
R
...
8 to 20 µm or 80020,000 nm of electromagnetic radiation
...
8 to 2
...
R
...
R
...
The region between 2
...
5 µm is the proper I
...
region
...

The correlation between the different units used in I
...
is given below:
1 µm = 106 m = 104 cm
1
10 4
=
cm1
λ µm
λ
Q
...
What are functional group and fingerprint region in I
...
?

ve

ν=

ni

So,

te

ch

no

lo

gi

ca

lu

Ans
...
5 to 7
...
In this region
functional groups of organic compound is detected
...
The fingerprint region can lead us to identify an organic compound
...
15
...
R
...
(a) IR source: A Nernst glower, a rod of an allow of Zirconium, Yttrium and
Erbium oxides
...

(b) Rock salt disc or KBr disc is used as glass and quartz absorb I
...

(c) Sample preparation: Either the sample with KBr is made to pellet or Nujol mull is
used
...

(d) Recording of spectra: The sample is placed in Rock salt cell in the path of I
...
The
change of intensity of light transmitted draws a graph which is IR spectrum
...
16
...
R
...
C = O (str
...
But
an absorption bond at 25003000 cm1 (broad) will be observed in spectrum of CH3COOH due
to dimeric association of CH3COOH molecules through hydrogen bonding
...
17
...
R
...

Ans
...
The peak at 1110 cm1 is
CO (str
...
So the compound is
CH3OCH2CH3
...
18
...
m
...
)?
Ans
...
If the particles in a nucleus dont have
their spins paired, there is a net spin
...
Thus a proton or nucleus acts like
a tiny bar magnet
...
The magnetic property of the nucleus is responsible for nuclear magnetic
resonance
...
blogspot
...
PM5

543

...

bl

one to the other and the absorption or emission of energy then takes place by the nucleus and
nuclear resonance then occurs
...
m
...

Q
...
What are equivalent and non-equivalent protons in n
...
r
...
Protons present in a molecule having the same environment absorb at the same
magnetic field strength
...

And protons which have different environments in a molecule absorb at different magnetic
fields, such protons are called non-equivalent protons
...
m
...
spectrum
...

ni

Q
...
Give a schematic diagram of pmr spectrum
...
See text
...
21
...

(i) CH3CBr2CH3 and (ii) CH3CH2Cl

ca

a

a

a

b

2

lo

gi

Ans
...
So n
...
r
...
e
...
So two signals are
obtained in the n
...
r
...
The upfield signal is a triplet (3H, t)
...
CH 2 protons give downfield signal as the C2 is attached to
electronegative Cl atom (See text)
...
22
...
In the NMR spectrum of a compound, the electrons around the protons also play
their role
...
This induced magnetic field
may reinforce or oppose the applied field
...
H is
related to Ho as H = Ho (1 σ) where, σ ⇒ a nondimensional quantity known as
shielding or screening constant and has a positive value
...
A greater applied field is required for
the excitation of protons
...

Shielding causes a shift of the resonance frequency to higher values of the applied field
(Ho) i
...
, the shift is upfield
...
e
...
The magnitude of this
shift is called chemical shift
...
blogspot
...
PM5

544

...

1

C—CH3

it

(i) H3C

CH3
3
3

(iv) CH3OCH2CH3

3

ve

(iii) CH3OCH3

rs

(ii) C2H5OH

bl

Q
...
Match the number of signals of the compounds given:
Compounds
Signals

CH3

lu

ni

Ans
...
e
...
Since there is no non-equivalent protons in the molecule, all the peaks will be
singlet and no splitting will take place
...
It will be a
triplet for CH3 protons, a quarlet for CH2 protons and a singlet for OH proton
...

no

Compound (iv) will produce three signals
...
Hence a
singlet for OCH3 protons, a quartet for CH2 protons and a triplet for CH3 protons
...
24
...
Molecular
formula C9H12, singlet τ 3
...
75, 9H
...
(i) The formula C9H12 corresponds to the general formula of aromatic hydrocarbon
CnH2n6
...

ht
tp
:/
/k
er
al
a

(ii) The compound gives two signals and thus it indicates the presence of two types of
protons
...
22 due to three ring protons and singlet τ
7
...

Q
...
Count the number of signals for the following compounds:

CH3

(1)

,

(2) CHCl2CH3

Ans
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH24-2
...
c
ot
og

ENGINEERING CHEMISTRY

(ii) The second compound contains two kinds of protons as indicated by a and b (below)
...

So, two signals will be observed
...
26
...

Ans
...
It
has been observed that area under an NMR signal is directly proportional to the number of
equivalent protons that give rise to that signal
...
As for example,
in the case of peaks obtained for benzyl alcohol, the ratios of the areas under the peaks are
1:2:5, indicating that the three types of protons are in the ratio 1:2:5
...

Q
...
Mention the various uses of n
...
r
...

Ans
...

(i) For identification of functional groups
...
By studying the chemical shift of
compound, it becomes possible to establish what kind of functional group is present
in the molecule
...
It is possible to elucidate the structure of an unknown compound from the n
...
r
...
This is due to
the protons which under different environments give different chemical shifts
...

(iii) For comparison of two compounds
...
Two compounds which show same n
...
r
...

Q
...
Discuss the applications of mass spectroscopy
...

• Determination of molecular mass of a compound (known and unknown)
...
R
...

• The combination of gas liquid chromatography (glc) with mass spectrometry (ms)
is of great importance in modern chemical analysis
...

Q
...
Translate the following set of spectra to three isomeric organic
compounds
...
p
...
R
...
06 (3H, t), δ 2
...
43 (2H, q)
...
The IR band at 1715 cm1 indicates that the compound possesses a C = O group
...

The NMR spectrum readily excludes are aldehyde as there is no resonance at about
δ 9
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH24-2
...
c
ot
og
bl

O


B
A
CH 3  CH 2  C CH 3

it

y
...
Methyl group (B) and methylene group are both deshielded (moved to downfield)

ve

rs

by the adjacent C = O group
...
72
...
(a) Mention the wavelengths for visible, UV and I
...
radiations
...

2
...
State Beer-Lamberts law and deduce mathematical expression for the same
...
What are the different electronic transitions that take place on the absorption of UV light?
5
...

6
...

7
...
20
and path length = 2
...

(Ans
...
Mention the principles of I
...
spectrum
...
Indicate whether you will use I
...
or U
...
spectroscopy for distinguishing the following pairs of
compounds:
(a) CH2 = CHCH2OCH3 and CH3 CH2 COCH3
(b) CH3OCH3 and CH3 CH2 OH
(c) CH2 = CHCH2OH and CH3 CH2 CHO
10
...
What are equivalent and non-equivalent protons?
12
...
What is chemical shift?
14
...
m
...
?
15
...
What is mass spectroscopy? What is the principle of m
...
?
17
...
R
...
m
...

(iv) m
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH24-2
...
c
ot
sp
og
bl

it

y
...
In photochemical reactions, the reactant molecules are previously promoted
by absorption of light to their electronically excited state
...
Light of particular frequency corresponding to particular energy can cause the electron
of a molecule to move to higher energy level
...
Spectrophotometer is an instrument which
compares the intensity of transmitted light and incident light and gives the amount of energy
absorbed by the solution of a compound
...
Generally the colored compounds absorb in the visible
range, and possess a color complementary to that of which is absorbed
...
R
...
8 mm

1000
1

2
...
25
...
R
...

Under normal conditions, the molecules are constantly vibrating and rotating and these
motions can be quantized
...
Compared to the difference between the two electronic
levels the difference between the two adjacent vibrational or rotational levels is much smaller
...
Thus when a particular wavelength of light is absorbed there will be many possible transitions which may give rise to a
broad band, rather than giving a sharp peak
...

ε may be expressed as ε = E/cl
...

The wavelength where the absorption is maximum is denoted by λmax
...

The functional group which causes such absorption is called a chromophore
...
blogspot
...
c
ot
og

sp

549

PHOTOCHEMISTRY

bl

transitions require much less energy and are found in I
...
region whereas rotational transitions
are found in far I
...
regions
...

Singlet and Triplet States

ni

ve

rs

it

In organic molecules the electrons in the ground state are paired and have opposite
spin
...
The energy for
the triplet state is lower than the corresponding singlet according to Hunds Rule
...
e
...
Any type of transitions are not permitted rather
transitions between energy levels are governed by selection rules and several types of transitions
are forbidden
...
e
...

gi

ca

(b) Symmetry-forbidden transitionsnπ* transition in formaldehyde is forbidden since
overlaps of orbitals are forbidden
...
Hence
nomenclature of these excited states separately is important
...

The ground state is denoted by so and higher excited states as S1, S2, S3, T1, T2, T3 etc
...
Kasha has developed another system of expressing the electronic states in terms of
initial and final orbitals involved in transition
...
g
...

ht
tp
:/
/k
er
al
a

(ii) Saturated molecules with σ and non of bonding MO, e
...
CH3I, H2O
...
g
...

(iv) Unsaturated molecules with σ, π, and n MOs, e
...
, aldehydes, ketones, pyridine, other
heterocyclics etc
...

π MOs are formed by overlapping of px and py or hybridized orbitals to form double or
triple bonds
...
Hence the types
of electronic orbitals are σ, π, n, π* and σ*
...

The n → π* transitions have low probability and hence give weak absorption bands
whereas π → π* transitions are most important and give intense characteristic absorption (for
conjungated hydrocarbons)
...
Since the charge densities are different it shows different chemistry from
that of the ground state molecule, also because it has excess energy but weaker bonds
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH25-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

550

bl

A transition of electrons from the bonding to the antibonding orbital causes a triple
bond to become double, a double bond to become single and a single bond to disrupt
...

the

it

y
...
On excitation an
electron on O-atom is transferred to antibonding π MO and hence the molecule can twist along

C—O bond
...
For e
...
acetylene, which is linear in ground
state has a trans geometry with sp2 carbons in (π, π*) state
...

te

ch

no

lo

gi

ca

Excited phenol is more acidic and also ortho-para directing towards substitution in
benzene ring
...
7 in the
ground and excited states
...
In general, phenols, thiols and aromatic amines
become stronger acids on excitation whereas carboxylic acids, aldehydes, ketones and
heterocyclics become stronger bases
...

In the excited state, the dipole moment not only has different magnitude, but different
direction also
...

ht
tp
:/
/k
er
al
a

Highlights:

Laws of Photochemistry:

• Grotthurs-Drapper Law (First law):
Only that light which is absorbed by a system can cause chemical change
...

• Wigners spin conservation rule:
In any allowed electronic energy transfer process, the overall spin angular
momentum of the system should not change
...
Three situations can
lead to cleavage of a molecule
...
25
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH25-1
...
c
ot
og

E1

bl

E2

y
...
25
...
Two possible transitions are shown
...

lo

gi

(2) When the promotion is to a lower vibrational level v1 or v2 which lies within the curve
E2, the molecule may cleave
...
25
...

E2

Potential energy

ht
tp
:/
/k
er
al
a

te

ch

no

Franck-Condon principle states that promotion of an electron (1015 sec) is much
faster than the single vibration (1012 sec)
...

(3) In some cases as in Fig
...
3, the excited state entirely leads to dissociation
...
g
...
The photolytic cleavage may
break the molecule into two smaller molecules or into free radicals
...
Rarely the molecule breaks into two ions
...
25
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH25-1
...
c
ot
og

ENGINEERING CHEMISTRY

bl

Types of Photophysical Pathways

gi

vc

ca

lu

ni

ve

rs

it

y
...
Promotions
are from S0 to S1 states, as promotion from S to triplet states is forbidden
...
) and usually drop back to S1 state
...
The decay from the higher energy states
initially populates many vibrational levels of S1, but finally comes down to the lowest vibrational
levels of S1, which is therefore the only important excited singlet state
...
The pathways are shown and listed in modified
Jablonski diagram (Fig
...
4) and in Table 25
...

IC

vc

ISC

IC
S1

ch

no

lo

S2

vc

hn

ht
tp
:/
/k
er
al
a

te

ISC
T1

hn
hnf

vc

hnp

S0

Fig
...
4 Modified Jablonski diagram
...
blogspot
...
PM5

552

sp

552

...

bl

Table 25
...

S0 + hν → S1v
S1 + heat
S1v
S1 → S0 + hν
S0 + heat
S1
S1
T1 v
T1v
T1 + heat
T1 → S0 + hv
T1
S0 + heat
S1 + A (S0 ) → S0 + A (S1 )

ni

ve

rs

it

Excitation
Vibrational relaxation
Fluorescence
Internal conversion
Intersystem crossing
Vibrational relaxation
Phosphorescence
Intersystem crossing
Singlet-singlet transfer
(photosensitization)
Triplettriplet transfer
(photosensitization)

lu

T1 + A (S0 ) → S0 + A (T1 )

no

lo

gi

ca

(1) Energy absorption may promote molecule to a higher energy state like S2, S3, etc
...
obeying Franck-Condon principle
...

(2) The molecule in the S1 state can drop to some low vibrational level of S 0 at once
giving off the energy in the form of light within 109 sec
...
This process is
slow and not very common except for aromatics and diatomic molecules
...
25
...

(3) Intersystem crossing (ISC), involves non-radiative transition from singlet to
triplet states (S1 → T1) which is a forbidden pathway
...
The
molecule thus might cross from S1 to T1 states at a high vibrational level and then cascade
down to its lowest vibrational level of T1
...

(4) Molecule from the T1 state may return to S state by giving up heat (reverse intersystem
crossing) or light (radiative phosphorescence emission)
...
Thus T1 state has much longer lifetime
...
The process is called photo-sensitization,
the donor molecule D is called photosensitizer, and the acceptor reaches its excited state
...
blogspot
...
PM5

553

sp

553

PHOTOCHEMISTRY

...

bl

This energy transfer takes place according to Wigner-spin conservation rule, which states
that the total electron spin does not change after the energy transfer
...
Since triplet states are usually difficult to
prepare by direct irradiation hence triplet-triplet transfer is an important process of transferring
energy by photosensitization
...

Highlights:

gi

ca

lu

(i) Differences in charge distribution in various energy states of a molecule create
differences in the chemical and physical properties of excited and ground state
molecules
...

no

lo

(iii) Geometry of the molecules may change on excitation which has an important
effect on the photochemistry of the molecule
...

(v) After absorbing a photon, an atom or a molecule, if does not participate in
photochemical reaction, can return to ground state by any of the many
photophysical pathways, some of which are radiative and some are nonradiative
...
The triplet states have much longer
lifetime and hence they react chemically
...

There are several types of chemical reactions which can occur with excited molecules
...

(1) Simple cleavage into radicals
...
In
case of ketones, this reaction is called Norrish type I reaction which involves α-cleavage
giving rise to an acyl and an alkyl radical
...

R′ O R


O

hν

→

R′ C · + R·


O

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH25-1
...
c
ot
og

sp

555

PHOTOCHEMISTRY

bl

This dissociation is favoured if a relatively stable alkyl radical is formed and usually
favoured in vapor phase rather than in solvent
...

The other examples are cleavage of Cl2 to Cl atoms, cleavage of OO bonds in peroxy
compounds, and CN bonds in aliphatic azo compounds (since stable N2 is the product)
...
Aldehydes can also cleave to form CO and alkane
...
This is Norrish type II reaction
...
Sometimes
the intermediate can also cyclize to a cyclobutanol as side product
...

...

C—R¢

OH

R 2C

C—R¢

...
Intramolecular rearrangement
...
Photoisomerization
...

Ph
H

C=C
cis-isomer

Ph
H

hn

Ph
H

C=C

H
Ph

trans-isomer

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH25-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

556

hn

Ph—C—Ph

O
(S1)

O
(T1)

O

rs

Ph—C—Ph

ve

Ph—C—Ph

it

y
...
When the excited molecule
returns to the ground state (So) either of the isomer can be formed
...
Hydrogen atom abstraction
...

ni

OH

lu

Ph—CH—Ph

ca

Ph—C—Ph
Ph Ph

gi

OH

no

OH OH
6
...

nCO2 + nH2O

hν

→
680 nm

(CH2O)n + nO2

Chlorophyll

All the oxygen comes from H2O
...
The photosystem consists of two partsan antenna complex
consisting of chlorophyll molecules which absorb the solar energy and the second part is
photochemical reaction centre, which is a transmembrane protein-pigment-cofactors complex
...
e
...
The overall photosynthetic conversion
involves light absorption at two different wavelengthsPhotosystem I (PS-I) and Photosystem
II (PS-II)light reactions
...

(a) Photosystem I (P 700)
...
The bound ferredoxin in turn transfers the electron to solubleferredoxin, which again transfers it to NADP+ forming NADPH (Fig
...
6)
...
blogspot
...
PM5

556

...
6

y
...
4

it

–0
...
2

ca

+0
...
25
...

gi

Non-oxygen evolving photosynthetic bacterium contains PS-I only
...
In oxygen-evolving systems PS-I and PS-II are serially linked to
produce NADPH and ATP by a two-step process
...
6

–

Redox potential (V)

ht
tp
:/
/k
er
al
a

te

e

+

+

NADP + H
NADPH
0

Q (weak reductant)

e

–

–

e
–

e
+0
...
8

H2O

O2 + 4H

photon
hn

(weak oxidant)

Photosystem II
P680

photon hn
+

(strong oxidant: Mn-containing,
water-splitting enzyme)

Fig
...
7 Electron transport and oxidation of H2O in noncyclic photo-phosphorylation (Z-scheme)
...
The final electron-carrier from

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH25-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

558

y
...
PS-I accepts electrons from PS-II
...
25
...
Light
energy causes electrons to flow from H2O to NADPH
...
25
...

Stroma side
+

2H

+

Photon, hn

ADP+Pi
+

+

ATP

NADP

lu

ni

NADP + H

ve

Photon, hn

rs

DmH = +ve

–

PQH2

no

2e

+

te

DmH = –ve

ht
tp
:/
/k
er
al
a

H2O 0
...
25
...
(1991)
...

4 hν

2H2O + 2NADP+ + 3ADP3 + 3HPO2 → 2H+ + O2 + 2NADPH + 3ATP4
Chloroplasts can also synthesize only ATP without producing NADPH involving cyclic
photophosphorylation
...
The NADPH and ATP formed by the light reactions are utilized for
synthesizing carbohydrates from CO2 in stroma for which sunlight is not required
...

Plants generate glyceraldehyde-3-phosphate (GAP) as the starting material for higher
carbohydrates from three molecules of CO2 by utilising 9 ATP and 6 NADPH
...

3CO2 + 9ATP + 6NADPH + H2O → GAP + 6NADP+ + 8 Pi + 9 ADP
...
blogspot
...
PM5

558

...

(i) Outer segment consisting of stack of membrane discs in rods and cones, which acts
as antennae for receiving photons (containing lipoprotein complex, which is specialised
for photon reception)
...

rs

(ii) Inner segment of metabolic and nuclear sources
...

lu

ni

Absorption of light leads to the photo-isomerisation of cis-retinal to trans isomer, which
dissociates spontaneously to all-trans-retinal and opsin
...
A general scheme of photoreaction is:
(i) Absorption of a photon of light causing 11-cis-retinal to all-trans-retinal form and
conformational change of opsin
...
Rhodopsin Rh is activated to Rh*
...

Photoabsorption alters the membrane potential and conductance of Na+, resulting in
transient opening of Na+ channel and Na+ ion influx
...

Absorption of a single photon blocks the influx of million of Na+ ions by closing hundreds
of
channels in the membrane
...

Na+

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH25-1
...
c
ot
og

ENGINEERING CHEMISTRY

Perception of color is by (a) additive and (b) subtractive processes
...

bl

In additive process perception of color is by mixing of primary colors, red, blue and
green
...

In subtractive process, pigments absorb certain colors and reflect back other colors
...
Each pigment absorbs
one primary color and reflects back the other two
...

ni

ve

Highlights:
• The initial photon absorption gives rise to a short lived singlet state which
subsequently passes to long-lived triplet state, which actually participates in redox
chain
...

gi

EXERCISES

te

ch

no

lo

State: (a) Grotthurs-Drapper law (b) Stark-Einstein law
...

Mention physical processes undergone by excited molecules
...

What is Norrish type I reaction? Give example
...

What are the Dark and Hill reactions?
Give a schematic representation of energy transduction in the noncyclic photosynthetic reaction
process
...
Explain photosynthesis in the light of photochemical reactions
...

2
...

4
...

6
...

8
...

10
...
blogspot
...
PM5

560

sp

560

...

bl

26

ve

rs

Role of Metals in Biology

ht
tp
:/
/k
er
al
a

te

ch

no

lo

gi

ca

lu

ni

Metal ions are required for many critical functions in biological systems
...
The elements
Elements required in Human
required in human nutrition can be grouped into
nutrition
bulk and trace groups
...
The transition metals for which
• Magnesium
biological storage and transport are significant are
• Sodium
in order of decreasing abundance: iron, zinc, copper,
• Potassium
molybdenum, cobalt, chromium, vanadium and
Trace elements
nickel
...
The
• Iron
metals are generally found either bound directly to
proteins or in cofactors such as porphyrins or
• Manganese
cobalamins
...

• Zinc
In this respect, the redox properties of the metals
are important, in others metals appear to contribute to the structure of the active state
...
1)
...
1: Some Enzymes Containing or Requiring Essential Inorganic Elements as Cofactors
Fe2+ or Fe3+
Cu2+
Zn2+
Mg2+
Mn2+
K+
Ni2+
Mo
Se

Cytochrome oxidase
Catalase
Peroxidase
Cytochrome oxidase
DNA polymerase
Carbonic anhydrase
Alcohol dehydrogenase
Hexokinase
Glucose 6-phosphatase
Arginase
Pyruvate kinase
(also requires Mg2+)
Urease
Nitrate reductase
Glutathione peroxidase

561

http://keralatechnologicaluniversity
...
com

...

bl

Iron is the most abundant transition element in the Earths crust and in general in all
forms of life
...
Iron is absorbed in its ferrous form (Fe2+)
...
Iron present in different food varies in their
absorption characteristics, such as iron is best absorbed from meat, less absorbed from cereal
grains
...
A much smaller amount is present in
myoglobinwhich is a muscle oxygen-transport protein
...
Iron transport from the storage sites to locations where cells synthesize
iron containing proteins is done by an iron-containing protein called transferrin
...
The liver, spleen and bone marrow contain much ferritin
...
Since during menstruation, iron loss becomes
double or triple, hence large amount of iron is required for women compared to men
...
26
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH26-1
...
c
ot
og

sp

563

ROLE OF METALS IN BIOLOGY

bl

The processes and reaction in which iron participates are crucial for the survival of
organisms and they include DNA synthesis, respiration, photosynthesis, nitrogen reduction,
oxygen transport and oxygenations
...

Deficiency of iron leads to iron-deficiency anemia, in which the number of red blood
cells are normal but the amount of hemoglobin in the cells is low
...
It is
required to the extent of 2
...

ni

Copper and iron proteins participate in many of the biological reactions:

lu

• for cytochrome oxidase synthesis which catalyzes the transfer of electrons from water
to dioxygen during respiration
...
g
...

ca

• activation of dioxygen
...

lo

Use of stored iron is reduced by copper deficiency, which suggests that iron metabolism
may depend on copper proteins
...
Hence animals that are copper deficient develop defective
collagen molecules (due to absence of cross-linking) leading to rupture of arteries
...
Here the copper atom carries the electron undergoing Cu(I)Cu(II) cycles
...
The enzymes include alcohol dehydrogenase, carbonic anhydrase, DNA
and RNA polymerases, carboxy peptidase
...

As a part of the carbonic anhydrase, it catalyzes the hydration of CO2 to H2CO3, whereas
in carboxypeptidases, it participates in proteolytic activity
...
The hormone insulin is stored complexed with zinc
...

Mechanism
Zinc has such an important role as the prosthetic group of large number of enzymes
since it can co-ordinate with four, five or six ligands without any preference
...
Zinc acts as a Lewis acid, it does not change its
protein ligand nor does it change its oxidation state but only changes the co-ordination sphere
on the side exposed to water/solvent
...
It
is therefore found to be bound to histidines, glutamates or aspartates
...
Thus from above it
can be said that zinc plays both structural and regulating roles for the enzymes
...
It is present in abundance in meat, egg,
sea foods, milk and liver but in low amount in fruit and green vegetables
...
blogspot
...
PM5

563

...

bl

Manganese plays a critical role in oxygen evolution catalysed by the proteins of the
photosynthetic reaction center
...
The superoxide dismutase
of bacteria and mitochondria and pyruvate carboxylase in mammals also contain manganese
...
Mn2+ also serves as a cofactor for phosphatetransferring enzymes
...
In different animals also Co is required for the synthesis of B12 by the
microorganisms of the G
...
tract
...

ca

Unlike most animals, ruminants have a high nutritional requirement for cobalt
...

gi

Nickel

ht
tp
:/
/k
er
al
a

te

ch

no

lo

Nickel is a component of urease, hydrogenase, CO dehydrogenase, S-methyl CoM
reductase, which catalyzes the terminal step in methane production by methanogenic bacteria
...
Nickel is a component of urease which
was the first enyme crystallized in 1926
...

Vanadium and chromium have several features in common
...
In
proteins, vanadium is a cofactor in an algal bromoperoxidase and in certain prokaryotic
nitrogenases
...
It is
found to function in the active sites of certain flavin dehydrogenases
...

Chromium is involved in the glucose uptake by animal tissues, but little is known about
the complexes or factors of chromium from plants, animals and bacteria
...
Mo proteins are also Fe-proteins with iron centres
...
g
...
Xanthine oxidase catalyzes the oxidation of purine to yield the excretory
product uric acid
...

Selenium combined in an amino acid is an essential component of the prosthetic groups
of several enzymes including glutathione peroxidase, which functions with glutathione to protect
cells against the destructive action of hydrogen peroxide
...
This is protected by
glutathione peroxidase which contains selenocysteine in which the S of cysteine is replaced
by Se
...
However, zinc and copper are bound to metallothionein in a form which may be stored
...
blogspot
...
PM5

564

...

bl

Zinc, copper, vanadium, chromium, manganese and molybdenum are transported as simple
salts or loosely bound protein complexes
...

Copper, cobalt, zinc, manganese and nickel, although essential in the diet, are also toxic
in excess and cause health hazards
...

Lastly silicon, ubiquitous as silica (SiO2) and as calcium aluminium silicate, is the
major component of clay and is required by rat, chick and other animals fed with synthetic
diet
...

Calcium and Magnesium

ca

lu

ni

The adult human body contains more than a kilogram of calcium, nearly all of which is
concentrated in bones and teeth along with phosphate and as insoluble crystalline calcium
hydroxyapatite
...

no

lo

gi

Ca2+ and the cytoplasmic Ca2+-binding proteins (e
...
Calmodulin) function as intracellular
messengers for different hormones
...

Transitory increase in the Ca2+ concentration which results from hormonal action on a
membrane receptor leads to the conformational changes of the Ca2+ binding proteins
...

ch

After these responses another important class of transport proteins (Ca2+ ATPases)
transport the excess intracellular Ca2+ (released from different sources) across the membrane
and maintain the original low concentration of Ca2+
...
In the plants Ca2+ forms link
between individual cells and is required for maintaining the rigidity of whole plants
...
Absorption of Ca from intestine is controlled by complex factors like pH, Ca:P ratio
in diet, presence of fatty acids and vitamin D in diet
...
The calcium present in the cereal grains is not
readily absorbed
...
Concentration
of magnesium is rather high in all the cells, i
...
, 5-10 mM, since it plays a vital role on the
action of a large number of enzymes involved in the glycolysis and ATP transport mechanisms
...
Magnesium is abundant in chlorophyll of green leafy
vegetables
...
Alcoholics and
elderly people are found to be magnesium deficient
...
Reducing and oxidising agents function as conjugate pairs (redox pairs)
...
blogspot
...
PM5

565

...

bl

Three types of redox centres are found in biologyprotein, small molecules and redox
cofactors
...

it

Nicotinamide adenine dinucleotide (NAD) and NADP participate with the 4-position of
the pyridine ring being active
...

lo

(b) Possess one hydrophobic shell close to cofactor which forms hydrogen bonds with the
hydrophobic environment to stabilize the oxidised and the reduced forms
...
These transferases are of
four classesflavodoxins, blue copper proteins, iron-sulfur proteins, cytochromes
...
They are
found mainly in bacteria and algae
...
The geometry of the copper
site is trigonal planar and three ligands bind to copper and have a relatively high reduction
potential
...
blogspot
...
PM5

566

...

bl

The iron-sulfur proteins play important role as electron carriers in all living organisms
and participate in the important functions like plant photosynthesis, nitrogen fixation, steroid
metabolism, oxidative phosphorylation etc
...
The ferredoxins (2Fe-2S) are found in plant chloroplasts and mammalian tissues
...
In these the Fe is
co-ordinated to the S of cysteins
...

Cytochrome contains heme cofactors and according to the type of heme i
...
, heme a, heme b
and heme c, cytochromes are also classified
...
Class II cytochrome c are found in
photosynthetic bacteria
...

gi

ca

lu

Electron transfer reactions play key roles in biological processes like collagen synthesis,
steroid metabolism, immune response, drug activation, neurotransmission, nitrogen fixation,
respiration and photosynthesis
...
26
...

Anabolic cycles
Organic
compounds
Photosynthesis

ch

Aerobic
respiration

no

Catabolic cycles

lo

CO2

ht
tp
:/
/k
er
al
a

te

ATP

ADP+Pi

Pi+ADP

2H2O

ATP

2H2O
O2

Fig
...
2 Aerobic respiration and photosynthesisComplementary processes
...

Similarly, the end products of aerobic respiration (CO2 and H2O) are the major nutritional
requirements of photosynthetic organisms
...
g
...
These reductants donate
electrons to the components of mitochondrial electron transfer chain leading to reduction of O2
to H2O
...
These reactions are coupled to ATP synthesis (called oxidative
phosphorylation)
...
NADH passes electrons to NADH-

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH26-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

568

it

y
...
FMN
accepts the electrons and is converted to FMNH2 and then passed to FeS
...
Cytochrome bc1 in turn passes the electrons to cytochrome c which again in turn
passes them to cytochrome oxidase
...

lu

ni

ve

rs

All the electron carriers in the electron transport chain interact according to their redox
potentials and it is obvious that the next electron acceptor has a higher affinity for electron
than the donor
...
The three
main protein complexesthe NADH dehydrogenase, cytochrome bc1 and cytochrome oxidase
act as H+ pump driven by electron transport and create an H+ gradient across the inner
mitrochondrial membrane to intermembrane space
...
26
...

3+

2+

Fe S

Succinate
dehydrogenase

lo

gi

Fe S

ca

FAD

FADH2

NADH

FMNH2

Fe S

CoQ

ch

+

Fe S
3+

CoQH2

te

NAD

2+

FMN

Cytochrome bc1 complex

no

NADH dehydrogenase

+

Cyt
...
b

Cyt
...
c1

3+

3+

Fe

Fe

Cytochrome oxidase
Cyt
...
c
2+

Fe

Cyt
...
a
3+
Fe
2+
Cu

+

H

ht
tp
:/
/k
er
al
a

H

Cyt
...
a3
2+

Fe
+
Cu

H2O
½O2

+

H

Fig
...
3 Details of electron transport
...

These electrons enter the main electron transport chain similar to that from the oxidation of
NADH
...

• Antimycin A inhibits the cytochrome bc1
...

Oxidative phosphorylation: Oxidative phosphorylation is ATP synthesis linked to the
oxidation of NADH and FADH2 via the electron transport chain
...
Energy liberated by electron transport is used to pump
H+ ions out of the mitochondrion and create an electrochemical proton gradient
...
About 3
molecules of ATP are synthesized per NADH oxidised and two ATP molecules per FADH2
oxidised
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH26-1
...
c
ot
og
bl

Highlights:

it

y
...
Calcium
also plays an important role in all animal cells as intracellular regulator
or messenger
...

ve

rs

• Magnesium plays an important role in the action of the enzymes of glycolytic
pathway and also in ATP-dependent reactions
...

lu

ni

• Iron is required for the synthesis of haemoglobin, cytochromes etc
...

ca

• Nickel, vanadium, chromium and silicon are needed for the proper growth of
bone and connective tissue
...

lo

gi

• Molybdenum is the part of the prosthetic group of xanthine oxidase
...

no

SHORT QUESTIONS AND ANSWERS

ch

Q
...
What are metalloproteins?
Ans
...
, e
...
, ceruloplasmin

te

(Cu)
...
2
...
In metal-activated enzymes the metal is not tightly held by the enzyme and can be
easily exchanged with other cations, e
...
, ATPase (Mg2+ and Ca2+)
...
g
...

Q
...
Which are the principal elements of the body?
Ans
...

They are Ca2+, Mg2+, P, Na+, K+, Cl, S
...
4
...
Vitamin D (calcitrol), parathyroid hormone, low pH (acidic), lactose and amino
acids like lysine and arginine promote Ca absorption
...
5
...
The Ca:P ratio is important for calcification of bones
...

Q
...
What are the biochemical functions of Mg?
Ans
...
Mg is also required for neuromuscular
functions
...
blogspot
...
PM5

569

...
7
...

bl

Ans
...
It is present in the proteins
in amino acids namely cystine, cysteine, methionine
...
8
...
Iron metabolism occurs in a closed system
...
Hence only the entry of iron in
the body by absorption is controlled and hence it is called the one-way substance
...
9
...
Hemocyanin is a copper-protein complex which functions like haemoglobin in
invertebrates
...
10
...
Fluorosis is caused by excessive intake of fluorine
...

lo

EXERCISES

What are the functions of minerals in our body?

2
...

What are the principal functions of Ca in our body?

4
...

5
...

What are the biochemical functions of Cu?

7
...

8
...

9
...

11
...

13
...

15
...

What is lysyl oxidase?
Explain the role of Zn in the body
...

What do you mean by bulk and trace groups?
What are cofactors? Give examples
...

18
...

20
...

What are electron transport and oxidative phosphorylation?
What are metalloenzymes?

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH26-1
...
c
ot
sp
og
bl

it

y
...
Using the term
environment we mean air, water and soil
...
Human being, the best form of life on earth, is ruling the earth and
for his comfort, power and thirst for knowledge has been constantly changing the natural
characteristics by adding toxic components to the environment and as a consequence every
living organism is facing environmental hazards
...
Apart from all these man-made problems
natural factors like volcanic erruptions, radioactivity and natural disasters also contribute to
pollution
...
The clean air is composed of the
gases having concentration
N2 → 78
...
9325%
O2 → 20
...
03%,
H2 → 0
...
0005%, Kr → 0
...
0018%

Air pollution has become an important factor of environmental degradation
...
produce a large amount
of polluting substances, that have damaging effect to human, plants and animal lives
...
have become prevalent due
polluted air
...
According to mode of formation,
pollutants which enter the air directly are called primary pollutants, and those which are
created in the air from pollutants under electromagnetic radiation from the sun are called
secondary pollutants
...
About 290
million tonnes of CO is discharged into the atmosphere annually, 90% of which originates from
571
http://keralatechnologicaluniversity
...
com

...
Out of man-made CO emission,
90% of it arises from transport sector
...

it

y
...
It
combines with haemoglobin in human blood to form carboxyhaemoglobin, which impairs oxygen
transport
...
CO also affects the cardiovascular system, causing heart diseases
...
On a global scale,
half of the ambient SO2 originates from the oxidation of H2S given off by decaying organic
matter
...
Main contributors are
burning of sulphur-containing coal and diesel in thermal power plants
...

gi

ca

Long term or chronic exposure to SO2 causes respiratory diseases like bronchitis,
particularly in young children
...
It causes corrosion of metals
...

lo

(iii) Sulfur trioxide (SO3)
It is formed by the oxidation of SO2 under the effect of sunlight
...

ch

no

Both the oxides of sulfur are converted to sulfurous and sulfuric acids in the atmosphere
with water vapours which is the cause of acid rain and is harmful for all living and non-living
forms on the earth
...
g
...
On a global basis, 60%
of NOx is produced from biomass burning, fixation by lightning, inflow from the stratosphere,
chemical conversion from NH3 in the troposphere and loss of NO2 from the soil
...

NOx have various direct and indirect effects on human
...
NOx readily
combines with water forming HNO3 which forms acid rain
...
In
presence of sunlight NOx and hydrocarbons (combustion products of petroleum) form smog
and this smog again causes eye irritation, breathing difficulties and limits visibility of roads
...

Acid Rain

Over the last few decades, simple rainfall has taken on a threatening complexity in
some parts of the world
...
This is known as
acid precipitation or acid rain
...

The longer the SOx and NOx remain in the atmosphere the greater is the chance of their being
converted to H2SO4 or HNO3 by various catalytic and photochemical reactions
...
blogspot
...
PM5

572

...

bl

Rains tend to be acidic naturally due to the dissolution of atmospheric CO2 to yield
H2CO3
...
also contribute
to the acidity
...
However
the contributions of SOx and NOx polluting the atmosphere contributes to disturb the balance
in the acidity, causing damage to the environment
...
causing faster weathering, (v) dissolves out metals and
salts that increase the content of these in natural water resources to even toxic levels, (vi) in
mist form damages the plants
...

(ii) Desulfurisation and denitrification of fuels leading to lower emissions of SOx and
NOx
...

SOx emission is reduced by coal cleaning, bio-desulfurisation of liquid fuel and other
methods of desulfurisation
...

Acid rains are likely to occur more in cities and industrialised areas and also in the
sectors where large amounts of these oxides are emitted by the automobiles
...
It comes mainly from the burning of fossil fuels, oxidation
of carbon stored in the trees and soil humus, and released when forests are fired for shifting
cultivation
...
Thus CO2 is used as main feed stock for the photosynthesis of green
vegetation
...
The excess of CO2
in the atmosphere causes respiratory disorders and suffocation
...
This increase in global temperature
further brings about the change in rainfall pattern, melting of ice in the polar region resulting
in rise of sea level, changes in fish production, forest and water supply
...
350 ppm and the
annual increase rate is about 1
...
Hence by the middle of the next century, CO 2
concentration in the global atmosphere will be approximately double the present concentration
...
The gases like CO2, water vapour, CH4 and man-made chlorofluorocarbons
act as glass in a green-house and allow the sunlight coming in but strongly absorb the infrared
radiation given out by the earths surface
...

Actually, the green-house gases are responsible for keeping our planet warm and
sustaining life, otherwise the temperature of the earth would have gone down to sub-zero
level
...
g
...
blogspot
...
PM5

573

...

bl

Venus is 60,000 times that of earth and average temperature of Venus is 425°C making
existence of life impossible
...
It is estimated that within 50100
years the temperature may increase by 4 to 5°C which will increase the surface water
evaporation and change the climate which may finally influence the growing of crops
...
It
also causes floods, hurricanes, tornadoes, and increased breeding of pests
...
Conservation of forests, reduction in use of automobiles, ban on
CFCs and nuclear explosions, encouraging and developing green technologies and checking
population growth and awaring people are the other alternatives to check the green-house
effect or global warming
...
e
...
It is formed in the stratosphere
by photochemical reaction:
O2 + hν (242 nm) → O + O

lo

O + O2 + M (such as N2 or O2) → O3 + M

ch

no

The species M absorbs the excess energy liberated in the reaction and the molecule of
ozone is stabilized
...
It is destructive to fabrics, rubber goods, crops etc
...

te

Ozone is destroyed by Cl2, released due to volcanic activity and also by reactions with
(i) NO, (ii) atomic oxygen, (iii) reactive OH radical present in the atmosphere
...
CFCs escape and accumulate at high altitude, undergo decomposition, under UV light,
the decomposition product being Cl2
...
5 molecules of
oxygen in chain reaction converting ozone to oxygen and thereby leads to depletion of ozone
layer
...
The use of CFCs were limited since then
...

The depletion of ozone layer allows the harmful UV radiations to reach earth which
finally causes skin cancer, sunburns, breast cancer, cataract, leukemia, lung cancer, visual
impairment, premature aging, DNA damage and even may lead to death
...
blogspot
...
PM5

574

...

bl

(vi) Hydrogen fluoride (HF)
It is given out from phosphate fertiliser industries, aluminium industries, metallurgical
processes, brick kiln and coal burnings
...

rs

it

(vii) Hydrocarbons
Different types of hydrocarbons in high concentrations present in the atmosphere cause
many serious problems like irritation to mucous membranes, respiratory problems, lung cancer,
nervous system disorders and even may cause death if in toxic level
...

lo

Particulates as pollutants

gi

ca

lu

ni

ve

(viii) Lead oxide (PbO)
Lead exists in a variety of chemical compounds with different characteristics
...
2 to 4 µg of lead is present per
litre of fuel
...
Adverse effects of lead are found in population with blood levels
of 10 mg/dl of Pb
...

Lead also enters the atmosphere from sources other than the automobiles, i
...
, from mining of
lead bearing ores, lead plumbing and soldering, use of paints and ceramic glass and lead-zinc
battery disposal
...
There are large number of sources of dust in the atmosphere, some of these
include mines, furnaces, vehicles, ceramic factories, forest fires, household dusts,
rubber tyre abrasion, natural winds etc
...
Silica containing dusts cause silicosis
...
Smoke is produced due to incomplete combustion of fuel, and the sources
are locomotives, power plants, incinerators, diesel and gasoline engines, open fires,
furnaces etc
...

(iii) Smog
...
It is of two types:
(a) London smog
...
The latter consists of a mixture of SO2
and SO3
...
This type of
smog causes respiratory problems, eye irritation etc
...

(b) Los Angeles smog (photochemical smog)
...
This is facilitated in sunny days
...

(iv) Asbestos
...
The tiny asbestos fibres penetrate the lung tissues and
mucous membranes and stay there for a long period
...

(v) Heavy metals
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH27-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

576

y
...
Presence of hydrocarbon group
helps it to pass through the membranes in our body; it mainly concentrates in blood, bones etc
...

ni

ve

rs

it

Similarly, mercury also reacts with SH group of different essential proteins and inhibits
enzymatic activities
...
Pure mercury, insoluble inorganic
mercury compounds have lower toxicities whereas soluble salts of mercury, mercury vapour
and organic mercury compounds like dimethyl mercury etc
...
Its
harmful effects include sore gums, loose teeth, brain damage, irritability and emotional
disturbances
...

OOCH2C

no

–

OOCH2C

N—CH2—CH2—N

lo

–

gi

ca

The best remedy for these heavy metals is treating with chelating agents like ethylene
diamine tetraacetate which removes heavy metals from the blood by forming complexes
...
Fuels used such as diesel, petrol etc
...
Burning or incomplete burning of these fuels causes
release of CO2, CO, SO2, NO2, hydrocarbons etc
...

This type of pollution can be minimised by using (i) better and pollution-free fuels,
(ii) using engines with better performances, (iii) using catalysts for the conversion of pollutants
to less harmful substances by joining a device in the exhaust system of an automobile
...
27
...

Thin coating of catalyst
on the ceramic
Out to
the air

From the
engine
CO/CO2
NOX
CXHY

N2
N2O
O2

Ceramic block with many
fine tubes

Fig
...
1 Catalytic converter
...
blogspot
...
PM5

576

...

Pollution:
(i) The excessive discharge or addition of undesirable substances or unwanted
foreign matter into the environment, thereby adversely altering the natural
quality of the environment, and causing damage to human, plants or animal
life
...

• Particulates like dust, smoke, smog, lead, mercury, cadmium
...
Acid rain
2
...
Depletion of ozone layer
4
...
Heavy metal poisoning

ht
tp
:/
/k
er
al
a

te

Air pollution can be controlled by preventing the formation of the pollutants at the
source
...
(a) Pollution due to emissions from automobiles can be minimised by using catalysts to aid the effective combustion
...
NH3, alk
...

2
...

(b) Installation of air treatment plants for the purification of vent gases containing
objectionable pollutants
...
The use of tall stacks or chimneys reduces the concentration of air pollutants in
the ground level
...

4
...

5
...
It is used for precleaning of air for removal of dry particulates
of size ranging from 520 µm
...
The centrifugal forces throw the particulates towards the
wall from where they settle down due to gravity
...
The action of cyclone separator is as shown in Fig
...
2
...
blogspot
...
PM5

577

...

Inlet for gas
containing
particulates

rs

Particulates move
outwards due to
centrifugal force

lu

ni

ve

Circular
spiral

gi

ca

Chamber

Outlet for deposited
particulates

lo

Fig
...
2 A cyclone collector
...
Smoke as well as the particulates can be
removed by this device
...
Smoke/air is passed through a chamber maintained to a
very high potential of 30,000 volts
...

Positive D
...
voltage

Point electrodes

Clean gas outlet

Dirty gas
inlet

Ground

Settled dust, carbon, etc
...
27
...

(c) Dust is eliminated by extraction ventilation
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH27-1
...
c
ot
og

sp

579

POLLUTION PREVENTION AND WASTE MINIMISATION

bl

(d) Filters
...

it

y
...
These are used to remove particle as well as acids and chemical
fumes
...

ca

lu

ni

ve

rs

6
...
Trees especially broad leaved plants help to reduce excess CO2
of the environment and also help to deposit the suspended particles from the air and
make air less polluted
...
Zoning
...
Thus dilution of the polluted air takes
place before reaching common people
...
Enforcement of Air (Prevention and Control) Pollution Act, 1981
...

WATER POLLUTION

te

ch

no

lo

gi

Water from nature is used by man for drinking, domestic, agricultural, transport and
industrial purposes
...

Water may be contaminated by the following:
1
...

2
...

3
...

4
...

ht
tp
:/
/k
er
al
a

5
...

Sources of Water Pollution Include
1
...
The domestic and municipal wastes consisting of human
excretions, kitchen wastes and other organic wastes drain out into the canal and
through it to the rivers and other natural water reservoirs deteriorating its quality
and also act as a source of food for micro-organisms
...

2
...
Acids, alkalies, metals, salts and numerous other chemicals
pollute the water
...
, contributes a lot of pollutants
to the water
...
Fertilizer plants
...
, to water
...
Agricultural discharges
...
, are the pollutants
...
Natural pollutants from other sources
...
, cause water pollution
which finally causes outbreak of infectious diseases
...
Processing of radioactive materials causes water pollution
...
blogspot
...
PM5

579

...

1
...

rs

3
...

it

2
...

ve

4
...
, polluted
water can be purified
...
By recycling of waste water before discharging involves treatments like use of activated sludge, trickling filter etc
...
Reclamation of waste water: sewage water can be made useable for irrigation, fishfarm raising, as it contains essential nutrients
...
Domestic-sewage has objectionable odour due to S and N containing
compounds and a grey to green color due to the presence of discharges from kitchens, bath and
lavatories
...
The treatments consist of aerobic and
anaerobic oxidations, which are brought about by the aerobic or anaerobic bacteria present
in the sewage
...

Sewage
+
Air (to
supply dissolved
oxygen)

Oxidation by
Aerobic bacteria

Nitrates, sulfates,
phosphates etc
...
(offensive odour)
...

Sewage

Oxidation by
Anaerobic bacteria

Oxidation to
produce H2S,
PH3, CH4 etc
...
blogspot
...
PM5

580

sp

580

...

bl

BOD of a sewage is defined as the amount of free oxygen required to oxidize the organic
matter present in the sewage by the aerobic bacteria present in it at 27°C for a period of
3 days
...
BOD, therefore, gives an idea of the level of
pollution of the sewage as it is an index of the amount of decomposable organic matter
...
An average sewage has a BOD level 100150 ppm
...

ca

lu

ni

A known volume of sample is diluted with dilution water (which is aerated to a known
dissolved oxygen concentration)
...
After this the
dissolved oxygen concentration is determined, the principle of which is given below
...

Principle for DO

gi

It is the modified Winkler method
...

lo

MnSO4 + 2KOH → Mn(OH)2 + K2SO4

no

2Mn(OH)2 + O2 → 2MnO(OH)2

ch

On acidification in presence of iodide, I2 is liberated in a quantity equivalent to the
dissolved oxygen present
...

I2 + 2S2O32 → S4O62 + 2I1
...
It represents both the
biologically oxidizable as well as biologically non-oxidizable impurities present and hence the
value is higher than the corresponding BOD of the sewage
...

Determination of COD

1
250 ml of the sample of water is refluxed for 1 2 hrs
...
After the oxidation is over the excess K2Cr2O7 is
titrated back with standard Mohrs salt solution
...

1 ml of 1N K2Cr2O7 ≡ 0
...

Municipal Sewage Treatment
Disposal of sewage has become of prime importance as it causes undesirable and harmful
effects on living beings and the environment
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH27-1
...
c
ot
og

Municipal sewage treatment processes are called sewarage and it involves the following

bl

steps:

ENGINEERING CHEMISTRY

sp

582

ve

rs

it

y
...
First the sewage is subjected to mechanical processes like
flowing, dilution and sedimentation to remove the coarse solid materials
...
Coarse materials
collect at the sedimentation tank called sludge
...

(ii) Secondary treatment
...
The aerobic process involves aerobic digestion of sludge by processes
like trickling filters, oxidation ponds and activated sludge process
...
It is sprayed over the bed when
it gets saturated with aerial oxygen and the micro-organisms present start aerobic digestion
while the water passes through the filter bed, degrading the organic compounds and finally
rendering the effluent harmless which collects at the bottom and enters the tertiary treatment
(Fig
...
4)
...
27
...

In the oxidation ponds which are shallow ponds the water is exposed to atmosphere
whereby the algae Chlorella pyrenoidosa grow and their growth helps in maintaining the
aerobic condition in the sewage and the microorganisms present digest the organic matters
present and render the water harmless
...
This settled sludge is the activated sludge which consists of a large number of
very actively metabolizing bacteria, yeasts, molds and protozoa
...
This method is also known as activated sludge
process
...

Anaerobic Digestion
The sludge collected after primary treatment is added to the anaerobic digestion tank
which is a closed tank and the micro-organisms digest the organic compounds in the absence of
oxygen for about 30 days
...
This gas can be used as a fuel for power generation or for city supply
...
of solid sludge
...
blogspot
...
PM5

582

...

bl

(iii) Tertiary treatment
...
This is subjected to chemical treatment
...
After this tertiary treatment the water is
safe for human use (Fig
...
5)
...
27
...

Water pollution can be prevented by:

ch

no

(a) Preventing the use of chemical fertilizers
(b) Using bio-degradable detergents
...

ht
tp
:/
/k
er
al
a

te

(d) Phyto-plankton, a layer of the tiny animals and plants that live on the surface of
sea water
...
The pollution in water hampers the growth of plankton and affects marine life
...

Sources of Soil Pollution
1
...
By excess
use of (NH4)2 SO4, the SO42 ion accumulates into the soil and makes it infertile due
to acidity
...
, causes
accumulation of Na+, K+ and leads to alkalinity of the soil
...
Soil is polluted by the cysts of entamoeba, ascaris, pigworm etc
...

3
...

4
...
These also enter the food chain and thereby entering human and animal
bodies
...

5
...

6
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH27-1
...
c
ot
og

ENGINEERING CHEMISTRY

sp

584

y
...
Soil is erroded due to removal of upper fertile layer
...
Dumping of wastes from mines, power generation plants and metal smelting cause
land pollution
...
Radioactive wastes discharged from industrial and research centres cause pollution
...
All sorts of chemicals in the atmosphere, plastic bodies ultimately lead to soil pollution
...

Before dumping the sewage the harmful chemicals should be removed
...

Avoiding the spillage of garbage, ash, sludge, bottles, plastics etc
...

Precaution to be taken to neutralise acid rain
...

8
...
, are to be avoided to protect the soil
pollution
...

2
...

4
...

6
...

RADIOACTIVE POLLUTION

ht
tp
:/
/k
er
al
a

te

ch

no

lo

This is mainly due to (i) nuclear explosions, (ii) discharges from nuclear reactors
...
These radio-nuclides
are sometimes very short lived and sometimes persist for thousands of years and hence create
both short time and long time hazards
...
, by different routes to different parts of the
earth and through the food chain they enter the biological processes
...

(b) Genetic damageradiations lead to chromosomal damage to any living system causing
permanent changes for generations
...

Radioactive wastes can be:

(a) High level wastes
...
They are intensely
radioactive and some of them have long half-lives e
...
, Plutonium-239, half-life 24,000 years
...

(b) Low level wastes
...

Disposal of radioactive wastes
Accidents from radioactive rays have increased public concern worldwide to lead to safe
disposal of these wastes
...

1
...
The wastes are either burried deep in the
ground away from dwelling areas, in vacated coal-mines, in salt-heaps (salts absorb
radioactive rays) inside mines
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH27-1
...
c
ot
og

sp

585

POLLUTION PREVENTION AND WASTE MINIMISATION

bl

2
...
Generally radioactive gases are stored in tanks, buried in the ground and finally
vented to air so that there is low level of activity in the air, otherwise it may be
inhaled and may enter the living system
...

3
...
For long term disposal ultimately the wastes are encased in non-corrosive
lead, titanium or copper containers and burried deep into the ocean
...

ni

ve

Radionuclides
Radionuclides are the products of the natural decay of uranium
...
Some of these
have long half lives, e
...
, Th-230 has a half life of 80,000 years
...

gi

ca

lu

The main exposure pathways for radioactivity from tailings are γ radiation, inhalation
of radioactive particulates, radionuclides entering the food chain
...
Both the long life and short life types of nuclides are of
concern for public health problems
...

lo

Table 27
...
Some Important radionuclides and their half -lives
Radionuclide

5760 years

Soft tissue, genital organs

27 years

ch

Thyroid

17 million years

Iodine-131

Thyroid

8 days

Plutonium-239

Bone, liver, spleen

24,400 years

Radium-226

Bone

1620 years

Strontium-90

Bone

28 years

Whole body

12
...
Noise pollution is expressed in Decibel units (dB)
...

Crowded cities, mechanised transport, heavy industries, modes of entertainment cause
noise pollution
...

WHO has recommended that a person can sleep upto 35 dB noise, 75 dB is the explosive
limit, 80 dB is harmful, damaging the hearing system
...
blogspot
...
PM5

585

...

bl

1
...

2
...

3
...

4
...

5
...

6
...

7
...

8
...

9
...

10
...

11
...

12
...

ca

Control of Noise Pollution

Noise pollution due to automobiles can be minimised by fitting silencers
...

Restricting the use of loud speakers
...

Planting Ashok, Neem, Eucalyptus trees on both sides of highways, beside school,
college, industrial buildings
...
The walls of living houses, office buildings, cinema halls should be covered with sound
absorbers
...
Noise creating machinery should either be lubricated regularly or covered with insulating materials
...
Wearing of earplugs, ear muffs for workers and others to minimise noise effects
...

2
...

4
...

THERMAL POLLUTION
The release of hot vapours from nuclear power plants, industrial effluents, nuclear
reactors, coal fired power plants, hydroelectric plants raises the atmospheric temperature and
causes thermal pollution
...
The dissolved oxygen concentration of water bodies
becomes low due to rise in temperature
...

By the combustion of coal and petroleum products CO2 concentration in atmosphere
increases which results increased temperature of the earth and green-house effect
...

• Oils, greases from automobiles, machines
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH27-1
...
c
ot
og
bl

(ii) Municipal sewage treatment

lo

gi

ca

lu

ni

ve

rs

it

y
...
Preliminary mechanical filtration
2
...
Biological treatment
(a) Aerobic process involving (i) Trickling filters, (ii) Oxidation ponds, and
(iii) Activated sludge process
(b) Anaerobic process
...

(v) COD
• Chemical oxygen demand is a measure of oxidisable impurities present in
sewage
...
1
...
See text page no
...

Q
...
What are the principal causes of pollution?

ht
tp
:/
/k
er
al
a

Ans
...

(ii) Rapid urbanization
...

(iv) Deforestation
...

Q
...
What are the undesirable effects of excess of oxides of sulfur in the
atmosphere?
Ans
...
572
...
4
...
The oxides of sulfur and nitrogen formed due to air pollution dissolve in the moisture
present in the atmosphere to form the corresponding acids, which fall with the rain slowly on
earth and lowers the pH of the rain water below pH = 5
...
5
...
Gases such as CO2, CH4, NO etc
...
This leads to about 0
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH27-1
...
c
ot
og

ENGINEERING CHEMISTRY

Q
...
What is the importance of ozone layer?

ht
tp
:/
/k
er
al
a

te

ch

no

lo

gi

ca

lu

ni

ve

rs

it

y
...
Ozone at an elevation of 30 km from the earths surface absorbs the most harmful
UV radiation coming from the sun and thereby protects the living beings on earth
...
7
...
Chlorofluorocarbons coming out from the exhaust of the supersonic jets and from
the refrigerators, aerosols etc
...

Q
...
What is photochemical smog? Mention its effects
...
See text page no
...

Q
...
What are effects of particulate matter on human?
Ans
...
The two most common diseases taking place are bronchial asthma and
lung cancer
...
10
...
The liquid waste, which includes human and household waters, industrial wastes,
street washing ground wastes containing mainly water and other organic and inorganic matters
is called sewage
...
11
...
The amount of free oxygen in mg required for the biological oxidation of the organic
matter present in 1 litre of sewage is called its biological oxygen demand (BOD)
...
12
...
Chemical oxygen demand (COD) is a measure of oxidisable impurities present in
sewage
...
13
...
BOD or COD is very important in sewage treatment since it indicates the amount
of oxidisable organic matter present in the sewage
...

Q
...
What is water table and how does it fall?
Ans
...

The water table falls when the rate of pumping out of water is greater than the rate of
rainwater percolation
...
15
...
Plants utilize the CO2 of air for their photosynthesis and give out O2 in the air,
thereby reducing the load of CO2 in air and enriching it with O2
...

Q
...
How can we decrease the lead pollution due to automobiles?
Ans
...

Q
...
What is eutrophication?
Ans
...
Thus formed thick layers of algae block out the light to plants growing below the
surface so that they can no more produce oxygen, and aquatic life becomes endangered
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH27-1
...
c
ot
sp
og
bl
y
...
blogspot
...
etc to
eduktu@gmail
...
blogspot
...
c
ot
og
bl

EXERCISES

Mention the harmful effects of the air pollutants: SO2 and CO
...

What is the difference between aerobic and anaerobic oxidations of sewage?
Describe the activated sludge process for treatment of sewage
...

Write down the principles involved in the determination of BOD and COD
...
Why is the ozone layer important for us?
Write the sources of radioactive pollution
...

(ii) Electrostatic precipitator and its use
...

(iv) Acid rain
...

(vi) Cyclone separator
...
What is noise pollution? How can it be minimised?
11
...
Explain (a) Pollution control can be effected by reforestation (b) BOD is the measure of pollution
of water
...
State the measures to be taken to control:
(a) Air pollution
(b) Water pollution
(c) Noise pollution
(d) Soil pollution
(e) Radioactive pollution
...
Discuss the methods of municipal sewage treatment
...
How can pollution from internal combustion engines be controlled?

ht
tp
:/
/k
er
al
a

te

ch

no

lo

gi

ca

lu

ni

ve

rs

it

y
...

2
...

4
...

6
...

8
...

http://keralatechnologicaluniversity
...
com
C-8\N-ENGCHE\ECH27-1

Title: best notes ever
Description: easy to learn

Buy These Notes Preview

Notesale: Turn your study into money

Already a Member? >

Search for notes by fellow students, in your own course and all over the country.

My Basket

Document Preview