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Unit 4 Chemistry

Useful formulas

Rate equation
Equilibrium constant

pH formula
Ionic product of water
Pure water

Weak acids expression

pKa formula
Buffer solutions expression

Kinetics Page 1

1
...


• Concentration of the reactants decrease
• Concentration of the products increase

Order

Effect

0

doesn't affect the rate of reaction

1

rate of reaction goes up 2 times

2

rate of reaction goes up 4 times

Overall total of orders

Kinetics Page 2

1
...
4 Rate determining step
• Most reactions take place in more than 1 step
• Short lived intermediates
• Intermediate species tell us about the mechanism
Rate determining step/ rate limiting step
• Slowest step, may form a bottleneck
• Any step after the rate determining step will not affect the
rate
• Species involved after the rate determining step do not
appear in the rate expression
...
1 Chemical equilibria
22 September 2015

•
•
•
•

18:55

Reversible reactions
Forward reaction rate = backward reaction rate
Closed system
Reverse reaction is significant
Equilibrium constant Kc

Kc = equilibrium constant

2
...
3 effects of conditions
22 September 2015

19:30

Type of
reaction

Temperature
change

Effect on Kc and effect on
products

Effect on
reactants

Direction
change

Endothermic

Increase

Increase

Decrease

Moves right

Endothermic

Decrease

Decrease

Increases

Moves left

Exothermic

Increase

Decrease

Increases

Moves left

Exothermic

Decrease

Increase

Decreases

Moves right

• If Kc is greater than 1 , products predominate over reactants and equilibrium is over to the
right
• If Kc is less than 1, reactants predominate over the products and equilibrium is over to the
left
Catalyst
• Increases the rate of forward and backward reactions equally
• Catalysts have no effect on the position
• Reduces activation energy
Factors

Concentration of
reactant

Pressure / volume

Increase

• Equilibrium will shift to • Equilibrium would
• Equilibrium would shift to
the right to the
shift to where there is endothermic reaction
increase in
fewer gas moles
...


Yield
products

Increases

Increases

Temperature

Decreases

Decrease • Opposite

• Equilibrium would
• Equilibrium would shift to
shift to where there is exothermic reaction
more gas moles

Yield
products

Decreases

Says the
same

Decrease

• Gas moles on both
sides has no effect on
equilibrium position

Equilibrium Page 6

Increases

Defining an acid
22 September 2015

18:56

Acid
• Substance donates a proton (H+ ion)
Base
• Substance accepts a proton (H+ ion)

H2O (l)

Acid

Base

H2SO4

HNO3

donates a proton accepts a proton

H+ (aq) + OH- (aq)

Pure water

Concentration of OH- ions = H+ ions
is used to find the pH of a base

Acids^J bases ^J buffers Page 7

3
...
3 pH of weak acids and bases
Expression for weak acids
Strong= fully dissociation
Weak= partially dissociation

Weak acid refers to pKa

Ka= acid dissociation constant(mol dm-3)

•
•
•
•

Large value of Ka
Further equilbriumtothe right
More the acid is dissociated
Stronger the acid

Acids^J bases ^J buffers Page 8

3
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Equivalence point
• Point where sufficient base has been added to neutralise the acid

Titration curves

1) strong acid- strong base

2) strong acid- weak base

3) weak acid - weak base

4) Weak acid - strong acid

Acids^J bases ^J buffers Page 9

3
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5 buffer solutions
Buffers
• Resist changes in acidity/ alkalinity
• When small amounts of acid/alkali is added the pH remains constant
How they work

• Keep [H+] and [OH-] concentration unchanged
• Based on an equilibrium reaction that will move in the direction to remove any
additional [H+] and [OH-] ions
HA(aq)

H+ (aq) + OH- (aq)

Acid buffers ( made of a mixture of a weak acid and soluble salt( from an acid)
...
g
...
1 Naming organic compounds
23 September 2015

19:02

Number of halogen Prefix
atoms or branched
chains

Number of
carbons

Prefix

1

Meth

2

Di

3

Eth

3

Tri

3

Prop

4

Tetra

4

But

5

Penta

5

Pent

6

Hexa

6

Hex

7

Hepta

Family

Formula

Suffix

Prefix

Example

Alkanes

-ene

Propene

Alkynes

-yne

Propyne

Halo alkanes

HaloChloromethane
(fluoro-,chloro-,
bromo,iodo-)

(x is F,Cl,Br,I)
Carboxylic acids

-oic acid

Ethanoic acid

Anhydrides

-oic anhydride

Easters

-oate*

Propyl ethanoate

Acyl chlorides

-oyl chloride

Ethan oyl chloride

Amides

-amide

Ethan amide

Nitriles

-nitrile

Ethane nitrile

Aldehydes

-al

Ketones

-one

Alcohols

-ol

Amines

-amine

Ethanoic anhydride

Ethanal
Propanone
Hydroxy-

Ethanol

Amino-

Ethylamine

Arenes

Methylbenzene

Naming Page 12

Symbol

4
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1 Carbonyl group compounds
28 September 2015

17:16

General formula Suffix

Reduced

Aldehyde RCHO

-al

Primary alcohol

Ketone

-one

Secondary alcohol

RCOR'

Physical properties of carbonyl compounds
• Strongly polar
(dipole dipole frorces between molecules)
• Higher Bp compared to alkanes of the same RMM
• Not as high Bp as alcohols with hydrogen bonding

Solubility in water
• Short chain ketones and aldehydes are soluble in water
• As the chain increases, the less it will dissolve
Reactivity of the carbonyl group
• C=O bond is strongly polar( big electronegativity difference)
•
is open to nucelophilic reagents to attack
• Nucleophilic addition is possible due to the double bond =

5
...
Use [O] for the oxidising agent
• One oxidising agent is acidified potassium dichromate with dilute sulphuric acid
...
3 carboxylic acids , esters
28 September 2015

Carbocyclic acids

18:04

Suffix

Properties of carboxylic acids

oic acid

1

• Soluble in water due to hydrogen bonds
• Have high mp due to the hydrogen bonds
compared to alkanes
• Characteristic smells
Esters

RCOOH
Naming
Count the carbon on the carboxyl acid as 1
When a functional group is attached to a
benzene ring then the carbon is not part of
the root
...
Name the methyl group which has been
replaced with the hydrogen
2
...
End in oate
• Have the general formula RCOOR'
• Short chain esters are very volatile and have
fruity smells ( used in perfumes and flavourings)
• Also solvents and plasticisers
• Fats and oils are esters with longer carbon chain

Carbonyl group Page 16

5
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5 acylation
29 September 2015

16:27

• Process by acyl group is introduced in to another molecule
• Group of compounds are called acid derivatives

Nucleophiles are attracted to the C + and is polar
...
Therefore it has been acylated
...
1 arenes
02 October 2015

17:13

Arenes
•
•
•
•

Hydrocarbons based on benzene C6H6
Benzene is an unsaturated molecule and is very stable
Called aromatic compounds
Below is Benzene skeletal formula

Bonding and structure of benzene
• Unsaturated and does not readily form addition compounds
• All the carbon to carbon bonds are the same

•
•
•
•

Delocalised = electrons spread over more than to atoms - in benzene there are 6 carbon atoms
Each carbon has 3 bonds: 1 hydrogen, 2 other carbon atoms
4th electron on each carbon atom is in a p orbital and there are 6 of these
They form an electron density

Stability
• Each carbon to carbon bond has 3 electrons - between a single - and a double= bond
• Delocalised system very important
• Makes benzene stable- aromatic stability
Thermochemical evidence for stability

Enthalpy

hydrogenation of cyclohexene is

Aromatic chemistry Page 23

hydrogenation of a ring an alternate double bond is 3 times of this

Benzene

6
...
3 Reaction of arenes
02 October 2015

17:37

Combustion
• Arenes burn with air with flames and smoke
• High carbon to hydrogen ratio
• Usually unburned carbon which produces soot
• Smoky flame = aromatic compound
Electrophilic substitution
• Leaves the aromatic system unchanged
• Addition requires delocalisation energy to destroy the aromatic system
Mechanism
1
...

3
...

5
...
1 introduction
08 October 2015

12:57

Amines = derivatives of ammonia where 1 or more hydrogen atoms have been replaced
with alkyl or aryl groups

Amines are useful for synthesis ( making new compounds)
Properties of primary amines

Boiling points
•
•
•
•

Primary amines have hydrogen bonds -NH2
Nitrogen is less electronegative than oxygen
amines hydrogen bonds are not as strong as alcohols
Short chain are gasses at room temperature

Reactivity
• Lone pair of electrons
• Gain an H+ ion (base)
• Electron deficient carbon atom - nucleophile
Solubility
• Primary amines soluble up to C4
• Form hydrogen bonds in less polar substances
• Phenylamine is not very soluble due to the benzene ring

Amines Page 27

7
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Comparing base strengths
• Strength of how readily it will accept a proton H+
Inductive effect= release of electrons from the alkyl group to the nitrogen atom
...
3 nucleophiles and synthesis
09 October 2015

16:36

Amines nucleophiles
Attack positively charged carbon atoms
Reactions with haloalkanes (aliphatic amines)
1
...
Primary amine( nucleophile ) will react with the haloalkane to produce a secondary amine
3
...
Tertiary amine (nucleophile) with react to give a quaternary ammonium salt
Further substitution
• Less pure product is formed
• secondary, tertiary amines and quaternary ammonium salts can be formed
Mechanism

Nucleophilic substitution

Amine preparation
1
...
Hydrogenation

Purer product as only a primary amine is formed
Making phenylamine
1) Benzene is reacted with conc H2SO4 and HNO3

Amines Page 29

2) Nitrobenzene is reduced to phenylamine using tin and HCL as reducing agents

Can also be written as :

• Since the reaction has been carried out with HCl , the salt
• Sodium hydroxide is used to liberate the free amine

is formed

Economic importance
•
•
•
•
•

Manufacture of synthetic materials such as nylon, polyurethane, drugs and dies
Quaternary ammonium compounds are used in manufacture for hair and fabric conditioners
Long hydrocarbon chain with a positively charged organic group( form cations)
Prevents the build-up of static electricity
Cationic substances

Amines Page 30

8
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2 peptides, polypeptides and proteins
Peptides= amino acids linked together
Polypeptides= molecules containing about 50 amino acids
Proteins= molecule containing over 50 amino acids
Amino acids and peptide links
• Amide - CONH2
• Amine group can react with the carboxylic acid group to form an amide linkage -CONHDipeptide formation

• A peptide with 2 amino acids is called a dipeptide
• dipeptide still retains the -NH2 and the -COOH group
• Can react further to give tri, tetra peptides

Peptide linkage

Peptide linkage

Particular protein will have a fixed structure
• -Ala-Glu-Ala-Leu-Tyr• Primary structure
• Polypeptides and proteins are condensation polymers- small molecule, water is eliminated as each link
forms

Hydrolysis
• Protein is boiled with HCL
• After 24 hours the mixture breaks down
• Peptide / protein break up in to amino acids
• All the peptide linkages are hydrolysed

Amino acids Page 32

• Amino acids can be separated and identified with chromatography

Structure of proteins

• Complex shapes held by hydrogen bonds
• Shapes of proteins are vital for their function (enzymes)
• Hydrogen bonding holds a helix shape

• Another arrangement of a protein is pleating (protein ends are pleated in to a shape)
• Hydrogen bonds can be seen below

Enzymes

Stretchiness of wool

• Efficient protein catalysts which occur in living system
• Acetate reactions
• Enzymes are very specific ( catalysing 1 reaction)
• Fit closely in molecules that they are reacting temporary:
○ Shape enzyme
○ Celeste's
○ Fits in to cavity (active site)
• Temperature and PH
 High temperature disrupts the hydrogen bonding
 Denature
 Optimum temperature
 Below optimum temperature- slow reaction
 Loses catalysis effect

• Wool is held by hydrogen bonds
• Wool is stretched by releasing
tension pf the H-bonds
• The wool retains its shape

Amino acids Page 33

Washing at high temperature
• Can break the hydrogen bonds and
loose its shape

Addition polymers
12 October 2015

13:10

Addition polymerisation
• Made from Joining monomers with a C=C double bond
• Form large chain molecules
• High pressures: high equipment costs

Monomer

Polymer

Biodegradability
• Inert
• Chemically unreactive
• Difficult to react
• Saturated alkane
• Single bonds

Name of polymer

Trade name

Poly (ethene)

Polythene( alkathene)

Poly( propene)

Polypropylene

Poly (chloroethene)

PVC (polyvinyl chloride)

Poly( propenenitrile)

Acrylic ( Arcilan,
courtelle)

Poly(phenylethene)

polystyrene

Polymerisation Page 34

Condensation polymers
Condensation polymer
• Two molecules react together
• Water or hydrochloric acid is eliminated
• Made from two different monomers with two different functional groups

Polyester

Polyamide

Polypeptide or polyamide
Disposal of polyesters and
polyamides
• Peptide linkage is broken
down with hydrolysis
• HCl
• Enzyme action

Recycling plastics
Advantages

Disadvantages

• Saving natural resources
(crude oil) to make raw
materials

• Plastics need to be collected,
transported, sorted
• Uses energy and manpower
• expensive

• Stops the build-up of
polymers on landfill sites

Esters
• Ester is formed when Carboxylic acids and alcohols react
• Water is eliminated

Polyesters
Polymerisation Page 35

Polyesters
• Ester linkage -COO• Need diols and dicarboxylic acids

Poly(amides)

• Functional group -CONH• Need a diamine and a dicarboxylic acid
• Examples nylon and Kevlar
Nylon -6,6

• Made form hexane-1,6-diamine and 1,6-hexanedioc acid
• The reaction goes faster with a diacid chloride rather than dicarboxylic acid
• HCL would be eliminated

Polymerisation Page 36

Kevlar
• Made from benzene-1,4-diamine and benzene-1,4-dicarboxylic acid

Peptide linkage

PET( Terylene)
• Made from benzene-1,4-dioc acid and ethane-1,2-diol

Polypeptides and proteins

• Made from amino acid monomers
• Each amino acid has an amine group and a carboxylic acid group

Polymerisation Page 37

Synthetic routes
12 October 2015

18:15

organic synthesis^J analysis Page 38

Organic analysis
14 October 2015

17:53

Test

Functional group

Positive result

Negative
result

Shake with bromine water Alkene
-C=C-

Red /brown colour goes colourless alkane

1
...
Acidify with HNO3
3
...
NH3

Iodine ion

+

Cl-(aq)

Ag+(aq) + I-(aq) → AgI(s)

yellow precipitate Insoluble , yellow ppt

organic synthesis^J analysis Page 39

conc
...
1 mass spectrometry
13 October 2015

13:52

1
...
Mr of a compound is the molecular peak (M peak)
○ Molecular ions have electrons knocked off

Carbon : 12C and 13C
Chorine: 35Cl and 37Cl ratio 3:1
Bromine: 79Br and 81Br ratio 1:1
M+1 peak tells us the number of carbon
atoms

Fragmentation(weaker bonds)- molecular ion is broken up in to
smaller fragments

• More stable the fragment, more likely it will form
• More abundant and higher peaks

Structural determination Page 40

11
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Beam Inferred(IR) radiation is passed through a chemical sample
2
...
Infrared frequencies of different bonds absorb

Fingerprint region identifies a molecule
•
•
•
•

Region between 1000cm-1 and 1550cm-1
It is unique for each particular compound
Matches with a known sample
Extra peaks can identify any impurities: how pure the compound is?

Structural determination Page 41

11
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Generates energy change in the nuclei

Magnetic field

Chemical shift
•
is measured in parts per million (ppm)
• Relative to tetramethylsilane (TMS)
TMS is inert
13C

NMR
1
...
One peak for each carbon environment a molecule has

Two carbon environments
Different atoms, each have
different amount of
electron shielding

, =205 ppm

, = 30 ppm

Three carbon environments
Structural determination Page 42

Three carbon environments

, =205 ppm

, = 37 ppm

Structural determination Page 43

, = 5 ppm

11
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7 peak is not split as it does not have
any neighbouring C atoms bonded to it, COOH
...
4 peak is split in to 4, has a
neighbouring C atom with 3 H atoms
...
1 peak is slit in 3, has a neighbouring C
atom with 2 H atoms
...
6 H nmr
25 October 2015

14:39

Value of n Type of splitting

n+1

0

Singlet

1

1

Doublet

2

2

Triplet

3

3

Quartet

4

TMS

• Single, singlet peak- easy to identify
• H atoms are highly shielded- does not interfere with other peaks - can be easily distinguished
from them
• Cheap and non-toxic

Butanone gives 3 peaks

Ethanol gives 3 peaks

Integration factor = the number of hydrogen atoms corresponding to the peak
Methylpropanal

butanone

Integration ratio 6:1:1

Integration ratio 3:3:2

Structural determination Page 46

11
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Gas liquid chromatography= separate mixtures of volatile liquids

2)

3)

1)

Nitrogen/
helium inert

GC
• Crude oil pollution
• Blood / urine drug taking

Structural determination Page 47



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