Page 262 - Chemistry ICSE Class X
P. 262
248 ICSE Chemistry – 10
Let us say it Again
Nitric acid occurs in the combined state in the form of nitrates, such as nitre, chile saltpetre, etc.
In laboratory, nitric acid is prepared by heating nitre (or potassium nitrate) with conc. sulphuric acid at less than 200°C.
On industrial scale, nitric acid is obtained by Ostwald’s process. In this process,
Ammonia is oxidised to nitric oxide.
Pt–Rh
4NH (g) + 5O (g) o 4NO(g) + 6H O
3
2
2
800°C
(1 : 8 by volume)
Nitric oxide is oxidised to NO by air. 2NO(g) + O (g) o 2NO (g)
2 2 2
Nitrogen dioxide is observed in water in the presence of air.
4NO (g) + 2H O(l) + O (g) o 4HNO (aq)
2 2 2 3
from air
The nitric acid obtained from Ostwald’s process is of about 50% strength. It can be concentrated to 68.5% by
distillation and further to 98% by dehydration with sulphuric acid.
Nitric acid is a monobasic strong acid.
Nitric acid
9 reacts with alkalis to give corresponding nitrates.
9 decomposes carbonates and bicarbonates to liberate carbon dioxide and the corresponding nitrates are formed.
9 Nitric acid is a strong oxidising agent. It oxides
H S to S, SO to H SO , ferrous salt to ferric salt and hydrobromic and hydroiodic acids to bromine and
2 2 2 4
iodine, respectively.
Nonmetals to the corresponding oxoacids: carbon to carbonic acid, sulphur to sulphuric acid, phosphorus
to phosphoric acid and iodine to iodic acid.
Conc. nitric acid reacts with metals to give metal nitrate, nitrogen dioxide and water.
Dil. nitric acid reacts with metals to give metal nitrate, nitric oxide and water.
A mixture of conc. HCl and conc. HNO in the ratio of 3 : 1 by volume is called aqua-regia. Aqua-regia can dissolve noble
3
metals such as platinum and gold.
Nitric acid is used
in the manufacture of nitrates, such as silver nitrate, explosives, artificial silk, dyes and nitro derivatives of organic
compounds.
for purifying gold, silver.
as an oxidiser in rocket propellants
in the etching of metals
