The Ostwald process template

Nitric acid manufacture for A-level and NCERT: catalytic oxidation of NH₃ to NO on a platinum–rhodium gauze at about 900 °C, oxidation of NO to NO₂ on cooling and absorption in water, with balanced equations and the oxidation state of nitrogen at each stage (−3 → +2 → +4 → +5).

What the template shows

• Ammonia → NO over a Pt/Rh gauze at about 900 °C → NO₂ → nitric acid
• Plant flow
• heat recovered
• Absorption tower
• NO₂ + water + air
• Nitric acid
• NO from the absorber is oxidised again with more air
• Oxidation state of N
• Pt/Rh gauze (≈ 90% Pt, 10% Rh), ≈ 900 °C, 4–10 atm, contact time about 1 ms · strongly exothermic
• gases cooled; NO is oxidised by more air
• absorbed in water; the NO is recycled
• the same absorption with excess air (overall for stage 3)
• overall: ammonia to nitric acid
• side reaction if contact with the gauze is too long
• oxidised by O₂ (gauze)
• disproportionation (and O₂)
• Ammonia from the Haber process is mixed with air and passed very quickly through a hot Pt/Rh gauze; the reaction is exothermic enough to keep the gauze glowing once started.
• The short contact time (about a millisecond) stops NH₃ being oxidised only as far as N₂ (side reaction); more than 95% of the NH₃ becomes NO.
• NO₂ dissolving in water is a disproportionation: N goes from +4 to +5 (HNO₃) and +2 (NO), and the NO is oxidised again and recycled.
• The product is about 60% HNO₃; distilling it with concentrated H₂SO₄ concentrates it. Most nitric acid is made into ammonium nitrate fertiliser; also explosives and nylon.
• Every part of this figure is editable · sources on the template card

Drawn with 50 shapes – every one editable in MolDraw.

Sources

• Housecroft & Sharpe, Inorganic Chemistry, 5th ed., Pearson 2018, ch. 15 Textbook
• NCERT, Chemistry Part I, Class XII (pre-2023 edition), ch. 7 The p-Block Elements Textbook