Nitric acid is manufactured through Ostwald's process, which involves the catalytic oxidation of ammonia by air over a platinum catalyst heated to 800°C, forming nitric oxide. The nitric oxide is cooled and oxidized to nitrogen dioxide, which is then absorbed in water in an absorption tower to produce nitric acid solution. The dilute nitric acid is further concentrated by distillation under reduced pressure to obtain approximately 98% nitric acid.

1. Nitric acid

2. Manufacture of nitric acid(Ostwald’s process):
Principle: The first and the important step in this process is the catalytic
oxidation of ammonia by the oxygen of the air, carried out in the presence of
platinum gauze heated to 800oc. Nitric oxide is formed during this process.
4NH3(g) + 502(g) → 4NO(g) + 6H2O(g)
Nitric oxide is cooled then it combines with more oxygen to form nitrogen
dioxide
2NO(g) + 02(g) → 2NO2(g)
Nitrogen dioxide is now converted to HNO3 by mixing it with water and air
4NO2(g) + 2H2O(l) + O2(g) → 4HNO3(l)

3. Fig: Manufacture of HNO3 by Ostwald’s
process

4. The process involve following steps:
1. Converter: NH3 is mixed with dust free air in the ratio of 1:8 by volume
and the mixture is passed through a converter made up of steel and packed
with platinum gauze catalyst. The converter is heated electrically to about
800oc where ammonia is oxidized to nitric oxide.
4NH3(g) + 502(g) →4NO(g) + 6H2O(g)
2. Cooling pipes: The gases escaping from the converter are cooled to about
50oc with the help of cooling pipes.
3. Oxidation camber: The gases are then passed through a chamber called
oxidation chamber where more of air is mixed. Here NO is oxidized to NO2.
2NO(g) + 02(g) → 2NO2(g)

5. 4. Absorption tower: Nitrogen dioxide is then introduced into the
absorption tower. It is packed with acid resistant stones. Water sprayed
from the top dissolves NO2 in presence of oxygen to give 60% nitric
acid. The waste gases are removed from the outlet.
4NO2(g) + 2H2O(l) +O2(g) → 4HNO3(l)
5. Concentration of the acid: Dilute HNO3 is further concentrated by
distilling it under reduced pressure in the presence of conc. H2SO4 to
get about 98% HNO3