Explain Ostwald process for manufacturing nitric acid. Draw structure of nitric acid and write its uses also.

Explanation

Manufacture of nitric acid by ost wald.s process. The outline of the plant and its working are shown below.
(i) Oxidation of ammonia : Ammonia prepared by Haber.s Process is mixed with 10 times its volume of dry air, The mixture is passed through a converter made of either steel or aluminium with platinum rhodium gauze placed in it. The temperature of the converter is kept at about 1070 K. Here the ammonia is oxidised to nitric oxide.
`4NH_3 + 5O_2 to 6H_2 O + 4NO + ` heat
This reaction is exothermic. Therefore, heating of the converter is required initially. Later on, the heat of reaction maintains the required temperature and no external heating is required.
(ii) Oxidation of nitric oxide : The nitric oxide coming out of the converter, is cooled and passed through a chamber where it mixes with oxygen and oxidised to nitrogen dioxide. It is called oxidising chamber.
`2NO + O_2 to 2NO_2`
(iii) Absorption of nitrogen dioxide : The nitrogen dioxide from oxidising tower is then passed through absorption tower. This tower is packed with acid-proof stone. Nitrogen dioxide comes into contact with spray of water and oxygen where it is dissolved to yield dilute nitric acid.
`4NO_2 + 2H_2 O + O_2 to 4HNO_3`
The dilute acid is collected at the foot of the tower. It is sprayed from top of the absorption tower again and thus concentrated. Further concentration of this acid may be carried out by distillation under reduced pressure.
Uses of Nitric acid :
In the manufacture of explosives, dụes, plastics and paints.
(i) As a laboratory reagent
(ii) For pickeling stainless-steel.