Question

Describe Ostwald’s process for the industrial manufacture of nitric acid. Write the balanced chemical equations of the following reactions: (i) Zinc metal reacts with conc. HNO$_3$
(ii) Iodine reacts with conc. HNO$_3$

Hint:

Remember: In the Ostwald process, NH$_3$ → NO → NO$_2$ → HNO$_3$. Also, conc. HNO$_3$ behaves as an oxidizing acid, producing NO$_2$ gas in most reactions.

Answer 1

Ostwald’s Process for Nitric Acid Manufacture:
The Ostwald process is the commercial method for producing nitric acid. It involves the catalytic oxidation of ammonia in three main steps: 1. Oxidation of ammonia to nitric oxide: \[ 4NH_3 + 5O_2 \; \xrightarrow{Pt/Rh, \; 500K, \; 9 atm} \; 4NO + 6H_2O \] 2. Oxidation of nitric oxide to nitrogen dioxide: \[ 2NO + O_2 \; \longrightarrow \; 2NO_2 \] 3. Absorption of nitrogen dioxide in water to form nitric acid: \[ 4NO_2 + 2H_2O + O_2 \; \longrightarrow \; 4HNO_3 \] Thus, nitric acid is obtained industrially using the Ostwald process. (i) Reaction of Zinc metal with conc. HNO$_3$:
Concentrated nitric acid is an oxidizing acid. With zinc, it forms zinc nitrate and nitrogen dioxide.
\[ Zn + 4HNO_3(conc.) \; \longrightarrow \; Zn(NO_3)_2 + 2NO_2 + 2H_2O \] (ii) Reaction of Iodine with conc. HNO$_3$:
Concentrated nitric acid oxidizes iodine to iodic acid.
\[ I_2 + 10HNO_3(conc.) \; \longrightarrow \; 2HIO_3 + 10NO_2 + 4H_2O \] Conclusion:
- The Ostwald process is the standard industrial route for nitric acid manufacture.
- Conc. HNO$_3$ acts as a strong oxidizing agent, oxidizing both zinc and iodine to their higher oxidation states while releasing NO$_2$.