Manufacturing Nitric Acid – Ostwald Process

Introduction

  1. Industrially, nitric acid is made by the catalytic oxidation of ammonia over heated platinum. 
  2. Oxidising ammonia produces oxides of nitrogen which can then be dissolved in water to produce nitric acid.

Reaction

  1. Initially, nitrogen(II) oxide will be formed from the catalytic oxidation of ammonia using the transition metal platinum.
    Ammonia + Oxygen → Nitrogen(II) Oxide + Steam
    4NH3 (g) + 5O2 (g) → 4NO (g) + 6H2O (g)
  2. The nitrogen(II) oxide is rapidly cooled before combining with oxygen (from excess air) to form nitrogen(IV) oxide.
    2NO (g) + O2 (g) → 2NO2 (g)
  3. The nitrogen(IV) oxide, mixed with excess air, is then allowed to react with water to form nitric acid.
    Nitrogen(IV) Oxide + Oxygen (air) + Water → Nitric acid
    4NO2 (g) + O2 (g) + 2H2O (1) → HNO3 (aq)

Uses of Nitric Acid

  1. Most of the nitric acid made is used to make the all-important fertilisers, such as ammonium nitrate.
  2. Other uses of nitric acid include making explosive, like nitroglycerine, or TNT (trinitrotoluene), and making dyes. Modern dyes are azo dyes, which can be formed by the reduction of various nitro-compounds.


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