Different acids differ in their ability to donate
protons. A strong acid is one, that is almost completely
dissociated (strong electrolytes) i.e. an acid that
produces large number of (H+) ions in aqueous
solution is said to be a strong acid. Typical examples
of strong acids are hydrochloric acid (HCL) nitric acid
(HHO3) and sulphuric acid (H2SO4).
A weak acid is one, that is only partially dissociated
(weak-electrolytes). Only a small fraction of the weak
acids transfer a proton to water. Typical examples of
weak acids are nitrous acid (HNO2),
phosphoric acid (H3PO4), hydro
fluoric acid (HF) carbonic acid (H2CO3)
acetic acid (CH3-COOH) and formic acid (HCOOH).
For example: In strong acid,
greater is the extent of ionization in water.
HCl + H2O
< ----- > H3O+
+ Cl+ (complete ionization in dilute
HF + H2O
< ----- > H3O+
+ F- (8.5% in 0.1 M solution)
CH3COOH + H2O
< ----- > H3O+
+ CH3COOO- (1.3% in 0.1 M
Similarly, the strong base is one, that is almost
dissociated completely (strong electrolytes), that is, a
base which yields large number of (OH-) ions
in aqueous solution, is said to be a strong base. Most
metal hydroxides, such as NaOH, KOH and Ba (OH)2
are strong electrolytes and strong bases.
A weak base is one, that is only partially dissociated
(weak electrolytes); weak bases dissociate to a small
extent in water to yield (OH-) ions.
Typical examples of weak bases are, NH4OH, Mg
(OH)2 and Be(OH)2, etc. Hence, the
relative strength of weak bases may be measured by the
extent to which they dissociate in water to yield
hydroxide ions (OH-).
A salt is ionic compound produced when an acid is
neutralized by a base. For example, sodium hydroxide
neutralizes hydrochloric acid to form sodium chloride
(salt) and water.
NaOH (aq) + HCI (aq)
NaCl (aq) + H2O (l)
Similarly potassium hydroxide neutralizes nitric acid to
form potassium nitrate and water
KOH (aq) + HCl (aq)
KNO3 (aq) + H2O (l)
On the basis of their chemical nature, salts can be
divided into three groups.
1. Normal Salts 2. Acidic salts. 3. Basic salts.
1. Normal Salts:
Salts which are formed by the complete neutralization of
an acid by a base e.g. NaCl, NaNO3, K2SO4
etc are normal salts. These salts do not have
replaceable hydrogen, atoms or hydroxyl groups.
2. Acidic Salts:
Salts which are formed by the partial neutralization of
an acid by a base e.g. NaHSO4, KHCO3,
etc are acidic salts.
NaOH (aq) + H2SO4
NaHSO4 (aq) + H2O (l)
KOH (aq) + H2CO3 (aq)
KHCO3 (aq) + H2O (l)
These salts contain replaceable hydrogen ion. They
react further with bases to form normal salts.
3. Basic Salts:
Salts, which are formed by the partial neutralization of
a base by an acid E.g. Mg (OH) Cl, Zn (OH) Cl, etc, are
Mg (OH)2 + HCl (aq)
Mg(OH)Cl + H2O (l)
These salts have replaceable hydroxyl groups. They can
further react with acids to form normal salts.
The crystalline compounds which are obtained, when two
specific salts are crystallized together are known as
double salts. These salts have definite chemical
composition. These compounds usually have definite
number of water molecules with them. Typical examples of
double salts are:
Potash Alum K2SO4 Al2
Chrome Alum K2SO4.Cr2
Carnalite KC1. MgCl2. 6H2O
Mohr's Salt FeSO4 . (NH4)2
9.4.1 Some important Commercial Preparation and uses of
Sodium carbonate: (Na2CO3.10 H3O)
Today sodium carbonate (Na, CO3) is
commercially prepared by the Solvay process or
ammonia soda process.
The raw materials are lime stone (CaCO3),
sodium chloride (NaCl), ammonia (NH3) and
The process involves the following steps:
Lime stone [CaCO3] is heated to yield calcium
oxide (quicklime CaO) and the CO2 gas.
CaO(s) + CO2 (g)
This (CO2) is passed into aqueous
solution of ammonia, and the ammonium bicarbonate is
NH3 (g) + CO2 (g) + H2O
This (NH4HCO3) reacts with
aqueous. cold solution of (NaCl) at 15°C, called Brine
to yield, sodium bicarbonate (NaHCO3), which
is not soluble at low temperature (15°C) and this
NH+4Cl-(aq) + NaHCO3(s)
This (NaHCO3) on heating yields sodium carbonate.
2NaHCO3(s) AH ΔHà
Na2CO3(s) + H2O (l) +
The ammonia (NH3) which is used as a raw
material in 2nd step discovered by reacting (CaO) with
2NH4Cl (aq) +CaO(s)
------à 2NH3 (g) +
CaCl2 (aq) + H2O(l)
Anhydrous sodium carbonate (Na2CO3)
is known as soda-ash and sodium carbonate decahydrate
commonly known as washing soda.
Uses of Sodium Carbonate (Na2CO3):
Sodium carbonate is soluble in water and has many
It is used in the softening of water. Sodium carbonate
furnishes carbonate ion (CO3) to precipitate
calcium and magnesium ions,
CaCl2 + Na2CO3
CaCO3 + 2NaCl
MgCl2 + Na2CO3
It is used as cleaning agent, and in making of soap,
detergents and paper.
It is used in making ordinary glass, which is used in
E.g. Na2SiO3(s) + SiO2(s)
Na2SiO3(s) + CO2T
Sodium Hydrogen carbonate (NaHCO3) (Baking
Sodium hydrogen carbonate (NaHCO3) or
baking soda is formed by "Solvay process", but mostly it
is prepared by passing the stream of CO2
through concentrated aqueous (Na2CO3)
Na2CO3(s) + CO2 (g) + H2O
Baking soda is used in the preparation of baking powder.
In the preparation of effervescent drinks and fruit
In medicines to remove acidity of stomach (i.e. as
In fire extinguishers.
Copper Sulphate (CuSO4.5H2O):
Copper sulphate or cupric sulphate which is also known
as blue vitrol or blue stone may be prepared by reacting
copper scraps with dilute sulphuric acid in the presence
2Cu(s) + 2H2SO4 (aq) + O2
------à 2CuSO4 (aq) + 2H2O
It can also be prepared by the treatment of CuO or CuCO3
with dilute sulphuric acid (H2SO4).
CuO + dilute H2SO4
CuCO4 + H2O
CuCO4 + CO2 + H2O
Uses of Copper Sulphate:
In textiles (mordant), tanning, electric batteries, hair
dyes and in electroplating.
As germicide, insecticide, preservative for wood, paper
In calico printing, making synthetic rubber and copper
salts e.g. scheels, green paint,
In paint and varnish industry.
A mixture of copper sulphate and milk lime is used to
kill fungus and molds.
Magnesium Sulphate (MgSO4.7H2O)
It is prepared by the action of H2SO4
and magnetite or dolomite, but nowadays it is prepared
by heating kiesserite under pressure with water.
MgSO4 + H2O + CO2 (g)
MgSO4 + CaSO4+ 2H2O +
MgSO4.H2O + 6H2O
pressure > MgSO4
Kiesserite (Epsom salt)
It is used as a mild purgative in
In dyeing and tanning processes.
In making fire proof fabrics.
As a filler in paper industry.
In manufacture of ceramics, glazed
tiles and match boxes.
Potash Alum (K2SO4.Al2
If equi-molecular quantities of potassium sulphate and
aluminum sulphate are dissolved in water and the
solution is allowed to evaporate. Crystals of (K2SO4.Al2
(SO4)3.24H2O) which is
called ordinary alum or potash alum are seperated out.
Alum is used in dyeing as mordant to fix insoluble dye
It is also used in tanning leather.
In sizing paper.
In purifying water.
As an antiseptic and as a mouth wash.
It also used in medicines.