Question

How is nitric acid prepared by Ostwald’s process?

Answer 1

Ostwald’s process is used for the manufacture of nitric acid on commercial scale. This method is based on the catalytic oxidation of ammonia by atmospheric oxygen and the formula for nitric acid is $HNO_3$

Complete step by step answer:
The reaction involved in Ostwald’s process are given below
Step1: In this step ammonia is oxidised in the presence of oxygen (atmospheric) in the presence of catalyst Pt/Rh gauze catalyst at 500K temperature and 9 bar pressure.
$4N{H_3}(g) + 5O{}_2(g)\xrightarrow[{500k,9bar}]{{Pt/Rh{\text{ }}gauze{\text{ }} catalyst }}4NO(g) + 6{H_2}0(g)$
As a result of the above reaction nitric oxide and water is formed.

Step2: Nitric oxide formed from step 1 readily combined with oxygen to give $NO_2$.
$2NO(g) + {O_2}(g) \to 2N{O_{2(g).}}$

Step3: Nitrogen dioxide formed in the step 2, dissolves in water to form nitric acid ($HNO_3$)
$3N{O_2}(g) + {H_2}O(l) \to 2HN{O_3}(aq) + NO(g)$
The aqueous nitric acid produced is concentrated by distillation to give 68% $HNO_3$ by mass.
And further concentration of nitric acid to 98% can be achieved by dehydration with concentrated sulphuric acid.

Note:
During the process there is formation of nitric oxide as a side product this nitric oxide is recycled. And for the concentration of nitric acid we use concentrating sulphuric acid because sulphuric acid is a dehydrating agent.
If we talk about the structure of nitric acid in a gaseous state, nitric acid exists as a planar molecule.