PREPARATION OF ACIDS
1.By direct combination of Elements.
Acids are mostly prepared by a direct combination of elements. For example, hydrogen chloride gas is prepared from hydrogen and chlorine under the action of an electric spark.
\(
H_2 + Cl_2 \xrightarrow{{sunlight}}2HCl
\)
\(
H_2 + S\xrightarrow{{boiling}}H_2 S
\)
2.From Non metals (By dissolving acidic oxides in water):
Elements such as carbon, sulphur, phosphorous etc. are burnt in oxygen and form their oxides.These Oxides when dissolved in water forms respective acids, and hence such non metallic oxides are called acidic oxides.
a) C + O2 \( \to \) CO2
Carbon + Oxygen \( \to \) Carbon dioxide
b) \(
CO_2 + H_2 O\xrightarrow{{}}H_2 CO_3
\)
Carbon dioxide + water \( \to \) Carbonic acid
c) S + O2 \( \to \) SO2
Sulphur + Oxygen \( \to \) Sulphur dioxide
d) \(
SO_2 + H_2 O\xrightarrow{{}}H_2 SO_3
\)
Sulphur dioxide + water \( \to \) Sulphurous acid
e) \(
SO_3 + H_2 O\xrightarrow{{}}H_2 SO_4
\)
Sulphur trioxide + water \( \to \) Sulphuric acid
f) \(
N_2 O_5 + H_2 O\xrightarrow{{}}2HNO_3
\)
Nitrogen pentoxide + water \( \to \) Nitric acid
g) \(
P_2 O_5 + 3H_2 O\xrightarrow{{}}2H_3 PO_4
\)
Phosphorous pentoxide + water \( \to \) Phosphoric acid
h) \(P_2 O_3 + 3H_2 O\xrightarrow{{}}2H_3 PO_3
\)
Phosphorous trioxide + water \( \to \) Phosphorous acid
i) \(
N_2 O_3 + H_2 O\xrightarrow{{}}2HNO_2
\)
Dinitrogen trioxide +water \(
\to
\) Nitrous acid
By the action of an acid on the salt of another acid:
Acid having a higher boiling point can react with the salt of an acid with a lower boiling point to produce an acid. For example, Sodium chloride (NaCl) is a salt of Hydrochloric acid (HCl). The boiling point of HCl is lower than that of H2SO4. Thus, when NaCl which is the salt of HCl reacts with H2SO4, HCl is formed.
H2SO4+NaCl \(
\to
\) NaHSO4+HCl
Volatile acids:
The acids, which easily changes into their vapours, either at room temperature or heating below 1000C, are called volatile acids.
Ex: HCl, HNO3, H2SO3 and H2CO3
Non-volatile acids:
The acids, which do not change into their vapours, even on strong heating are called non-volatile acids.
Ex: H2SO4