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10 th

ACIDS, BASES, AND SALTS

CHEMISTRY

Acids :- acids are substances which dissociate in aqueous solution to give hydrogen ions E
...

HCL

H2O H+ + Cl−

HNO3 H2O

H+ + No−3

Acids are sour in taste and turn blue litmus solution red
...
E
...

NaoH (aq)

H 2O

Na+ (aq) + OH- (aq)

Ca (oH)2 (S) H2O

Ca2+ (aq) + oH- (aq)

Bases have bitter taste and soapy touch and turn red litmus solution blue
...
for
example, hydrochloric acid (HCl), nitric acid (HNO3), sulphuric acid (H2SO4) are strong acids
because they are fully ionized in aqueous solutions
...

For example, acetic
acid
(CH3COOH), hydrocyanic acid (HCN), carbonic acid (H2CO3),
phosphoric acid (H3PO4)are weak acids because they are only partially ionized in aqueous
solutions
...


Strong Bases :- the bases which completely ionize to give hydroxide ions (OH−)are called strong
bases
...
For example,
NaOH (aq)

water

Na+ (aq)

+

OH−(aq)
...
For example, ammonium hydroxide (NH4 OH), calcium hydroxide
(Ca(OH2) are weak bases because they only partially ionize in water
...


Classification of Acids :- the acids are classified on the basis of number of hydrogen (H+)or
hydronium (H3O+) ions produced by the ionization of one molecule of the acid in aqueous
solution
...
Monobadic acids
...
Thus, the basicity of monobasic acids is
one
...
It dissociates in one step only as :
HCl

+

H 2O

H 3O + +

Cl− (aq)
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10 th

ACIDS, BASES, AND SALTS

CHEMISTRY

Since they have only one replaceable hydrogen atom, they form only one type of salts
...
Dibasic acids
...
Thus the basicity of a dibasic acid is 2
...
It dissociates in two steps as :
H2SO4

+

H 2O

H SO−4

+

H 3O + +

H 2O

H 3O + +

HSO−4
...

3
...
Acids which when dissolved in water produce three hydronium ions per
molecule of the acid are called tribasic acids
...
For example,
phosphoric acid, H3PO4 is a tribasic aicd
...

H3PO4 + H2O

H 3O + +

H PO4−

H2PO4− + H2O

H 3O +

+

HPO42−

HPO42− + H2O

H 3O +

+

PO43−

Since they have three replaceable hydrogen atoms, they form three series of salt
...
Monoacidic bases
...
For example, sodium hydroxide, Na OH
is monoacidic base and its acidity is 1
...


2
...
Bases which when dissolved in water produce two hydroxide ions per
molecule of the base are called diacidic bases
...

Ca (OH)2 (aq)

water

Ca2+(aq)

+

2OH−

3
...
Bases which when dissolved in water produce three hydroxide ions per
molecule of the base are called triacidic bases
...

Al(OH)3 (aq)

water

Al3+(aq)

+

3OH−
...
Reaction of acids and bases with metals :- acids react with metals to liberate hydrogen
gas
...
The metal combines with the remaining part of the
acids and forms a compound called salt
...
Some metals also react with bases to form hydrogen gas
...
The reaction may be written as :
2NaOH

+

Sodium
Hydroxide

Zn
Zinc

Na2ZnO2

+

Sodium zincate

H2
Hydrogen gas

Reaction of acids with metal carbonates and metal hydrogen carbonates :Acids react with metal carbonates and metal hydrogen carbonates (also called
bicarbonates) to form the respective salts, water, and carbon dioxide
...

Metal + Acid
metal salt + water + carbon dioxide
Carbonate
Na2CO3(s) +
2HCl(aq)
2NaCl(aq) +
H2O +
CO2(g)
Sodium
Carbonate

CaCO3
Calcium
Carbonate

Hydrochloride
acid

+

HCl(aq)
Hydrochloric
acid

sodium
chloride

water

CaCl2(aq)
calcium
chloride

H2O +

CO2(g)

water

+

carbon
dioxide
Carbon
dioxide

Similarly, metal hydrogen carbonates (or bicarbonates) give carbon dioxide
...
In all acid-base reactions
both acids and bases lose their character
...
In general, a
neutralization reaction may be represented as :
Acid + Base
Salt + Water
For example, the reaction between hydrochloric acid and sodium hydroxide may be
written as :
HCl (aq) + NaOH(aq)
NaCl(aq) + H2O(l)
Reaction of metallic oxides with acids :
Acids react with merallic oxides to form their respective salts and water
...
For
example, sodium hydroxide reacts with carbon dioxide to form sodium carbonate and
water as :
2NaOH(s) +
CO2(g)
Na2CO3(aq) +
H2O(l)
Soduim
Hydroxide

Carbonate
dioxide

Sodium
carbonate

Calcium hydroxide solution is basic and it reacts with carbon dioxide to give salt and
water
...

Metal sulphide
+
Acid
Salt
+
Hydrogen sulphide
Hydrogen sulphide has the smell of rotten eggs
...

pH may be defined as a number by which negative power of 10 has to be raised in
order to express the concentration of hydrogen ion of the solution in moles per litre
...

pH may also be defined as :
Negative logarithm (base 10) of the hydrogen ion concentration in moles per litre
...
The pH may
simply be thought as a number which indicates the acidic or basic nature of the
solution
...

1
...
It has equal concentration of H3O+ and OH− ions
...
For example, a sodium chloride
soltion or a sugar sollution are neutral, each having pH of 7
...
pH of basic solutions :
All basic solution have pH more than 7
...
As
the pH increases from 7 to 14, the basic character increases
...
pH of acidic solutions :
An acid solution having low pH value will be stronger acid than another solution having
higher pH value solutions, having pH between 0 to 2 are strongly acidic while those
having pH between 5 to 7 are weakly acidic
...

Salts :
A salt is a compound formed by complete neutralization of a base by an acid or an acid
by a base
...

Classific ation of salts :
The salts may be classified in the following ways :
1
...
A normal salt is oner which does not contain any
ionisable or replacieable hydrogen atoms in its molecule
...

For example, a normal salt sodium shloride (NaCl) is formed by replacement of hydrogen
from hydrochloric acid by sodium metal
...

2NaOH + H2SO4
Na2SO4 + 2H2O
2
...
These salts formed by partial replacement of replaceable hydrgen ion
are called acidic salts
...

For example,
H2SO4 + NaOH
NaHSO4 + H2O
In this case, the metal sodium replaces only one hydrogen ion from sulphuric acid
...

For example,
NaHSO4 + H2O
Na+ + H3O+ + SO24− (aq)
Acid salts further react with bases to form normal salts
...

3
...
The salts formed by the partial neutralization of a base by an acid are
called basic salts
...

Cu (OH) Cl + HCl
CuCl2
+
Basic copper
Chloride salt

hydrochloric
acid

H2O

copper (II) chloride
normal salt

Some other examples of basic salts are :
Cu (OH) NO3, Pb (OH)NO3, Pb (OH)Cl
4
...
The sals containing mote than onev cation or an-ion other than H+ or
H- ions are called mixedd salts
...

OCl
Ca
Cl
Bleaching Powder
Some other example are : NaKCO3, NaNH4HPO4 (microcosmic salt)
...
Double salts
...
For example, potash alum, K2SO4, Al2 (So4)3
...

Some other examples are :
FeSo4
...
6H2O
Mohr’s Salt
K2SO4
...
24H2O
Ferric alum
pH of Salts :
The salts may be acidic, basic or neutral depending upon the acid or base from which
they are formed
...

In general,

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10 th
•
•
•

ACIDS, BASES, AND SALTS

CHEMISTRY

Salts of strong acids and strong bases areneutral with pH value of 7
...
g Nacl,
Kno3
...

E
...
Cuso4, NHCL4
...
E
...

Na2Co3
...

Occurrence
...
At some places it is
mined from salt rocks
...
Its simplest formula corresponds to NaCl
...

Properties: (i) common salt is deliquescent i
...
, it absorbs moisture from the
atmosphere
...
(ii) Common salt is thermally very stable
(iii) Common salt is soluble in water
...

Uses: Sodium chloride although cheap, but is very important chemical compound
...

a) Common salt is used for manufacturing a large number of useful chemical
compounds such as caustic soda, soda ash (Washing soda), baking soda, hydrochloride
acid, chlorine gas etc
...

c) Common salt is used in freezing mixtures (Mixtures containing ice and solid granular
common salt)
producing low temperature
...

Manufacture
...

Some common examples of materails obtained from common salts are :
1
...

3
...


Sodium hydroxide
...
Sodium hydroxide, NaOH :
Sodium hydroxide is manufactured by passsing electicity through on aqueous solution of
sodium chloride (called brine), which dcomposes to form sodium hydroxide
...

2NaOH(aq) + Cl2(g) + H2(g)
NaCl(aq) + 2H2O(l) Electricity
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10 th

ACIDS, BASES, AND SALTS

CHEMISTRY

During electrolysis, chlorine gas, Cl2 is liberated at anode while hydrgen gas, H2 is
evolved at cathode
...

Properties :
i) Sodium hydroxide is a white crystalline, deliquescent solid
...
It alsoi neutralises acids
forming salt and water
...
e
...
On prolong exposure, sodium hydroxide absorbs CO2 resulting in the
formation of white crust of solid hydrateed Na2CO3 at the surface
...

v) An aqueous solution of sodium hydroxide contains large concentration of hydroxyl
ion (OH-) and precipitates insoluble metal hydroxides from solutions containing
metallic ions
...

(II) It is used in the petroleum refining
...

(IV) It is used in the textile industry for nurcirising cotton fabrics
...
e
...

(V) It is used as cleansing agent for machines and metal sheets
...

(VI) It is used for the preparation of pure fats and oils
...

(2) Washing Soda Na2 CO3
...
10H2O, (Sodium carbonate decahydrate)
...

Manufacture :
Sodium carbonate is manufactured by solvay process (also known as ammonia soda
process) as discussed below
(i)

When carbon dioxide gas is passed through a brine soltion (about 28% NaCl),
saturated with ammonia, it gives sodium bicarbonate
...
It is ignited to give sodium carbonate :
2NaHCO3

Na2CO3

+

CO2 + H2O

Sodium carbonate

Properties :
1
...
It
exists as a decahydrate (Na2CO3
...

2
...
It dissolves in water to form
an alkaline solution, which turns red litmus solution blue
...

3
...
This process of loss of water of
crystallisation from a hydrated salt to the atmosphere, on keeping it exposed to air
is called effloresecence
...


Na2CO3
...


Or

Na2CO3
...
On heating , above 373K, washing soda
does not decompose but loses all its water of crystallisation to form anhydrous salt
...

Na2CO3
...
10H2O
Na2CO3 +
10H2O
Sodium carbonate
(anhydrous)

Uses of Washing Soda (or sodium carbonate)
...

1
...

2
...

3
...

4
...

5
...

(3)

Baking soda, NaHCO3 (Sodium Bicarbonate)

The chemical name of baking soda is sodium hydrogen carbonate or sodium bicarbonate
...

Preparation: In laboratory, sodium bicarbonate can be prepared by saturating a cold
solution of sodium carbonate with carbon dioxide
...

Properties :
1
...

2
...
Therefore, it is used to neutralize an acid
...
It is amild non-corrosive base
...
Action of heat
...

2NaHCO3

Heat

Sod
...

(i) Sodium bicarbonate is used for preparing baking powder and effervescent drinks
...
It corrects the acidity in the stomach
(i) Sodium bicarbonate is used in old-type fire extinguishers
...
Baking powder is a
mixture containing sodium bicarbonate (NaHCO3) and an acidic compound such as
potassium hydrogen tartarate or citric acid
...

The CO2 so released makes the cake/ bread porous and fluffy (light weight and soft)
...
Bleaching powder, (CaOCl2)
Chemically, bleaching powder is calcium oxychloride, CaOCl2 or Ca(OCl)Cl
...

Ca(OH)2

+

Cl2

CaOCl2

slaked lime

+

H2 O

bleaching powder

Properties :
1
...

3
...


Bleaching powder is a yellowis white powder
...

It is soluble in cold water giving a milky solution due to free lime present in it
...
This is due to the fact that it reacts with carbon
dioxide present in air to produce calcium carbonate and chlorine gas
...
Reaction with dilute acids : when bleaching powder is treated with an excess of a
dilute acid (like HCl or H2SO4) all the chlorine persent in it is liberated
...

+
2HCl
CaCO2
+
H2O + Cl2
CaOCl2
Calcium
Oxychloride

CaOCl2

calium
chloride

+

H2SO4

bleaching
Powder

CaSO4

+

H2O + Cl2

calcium
sulphate

Uses: Bleaching powder is used
i
...
As a disinfectant and germicide
...
For sterilizing water
...
As an oxidizing agent
...
1/2 H2O)
Plaster Of Paris is hemi-hydrate sulphate of calcium
...
½
H2O or (CaSO4)2
...
2H2O) at 120 –
125oC
...
2H2O]
gypsum

or

∆, 1200C

(CaSO4)2
...
2H2O

∆, 1200C

CaSO4
...
It is a white powder
...
It absorbs water with evolution of heat
...
When mixed with water, it forms a paste which sets into a hard mass
...
The setting of Plaster of Paris is due to its
hydration into gypsum
...
H2O + 3H2O

2 CaSO4
...

iii) Plastering the fractured bones to keep the joints in a fixed position
iv) Making black board chalks
Water of Crystallisation:
Water of crystallisation is the fixed number of water moleculees present in one formula
unit of a salt
...
For example, five water molecules are
present in one formula unit of copper sulphate, som the chemicasl formula of hydrated
copper sulphate is CuSo+4+
...
Similarlym ten water molecules are present in one
formula unit of washing sodal
...
2H2O

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