ICSE Class 10 Chemistry: Ammonia — Complete Notes 2026

Preparation of Ammonia

• Lab: Ca(OH)₂ + 2NH₄Cl → CaCl₂ + 2H₂O + 2NH₃↑ (heat)
• Industrial: Haber Process: N₂ + 3H₂ ⇌ 2NH₃; iron catalyst; 450–500°C; 200 atm pressure
• Conditions chosen as compromise: lower temperature increases yield but slows rate; 450°C balances both

Physical Properties of Ammonia

• Colourless gas with pungent smell; lighter than air (lower density); very soluble in water (1:700)
• Fountain experiment: NH₃ very soluble in water; water rushes into flask forming fountain; solution turns pink (alkaline)
• Condensation: NH₃ liquefied under pressure; used as refrigerant; low boiling point −33°C

Chemical Properties

• Alkaline: NH₃ + H₂O → NH₄⁺ + OH⁻; turns red litmus blue; pH > 7; weak alkali
• Reaction with acids: NH₃ + HCl → NH₄Cl (white fumes; test for NH₃ or HCl gas)
• Reducing agent: 4NH₃ + 3O₂ → 2N₂ + 6H₂O (combustion); catalytic oxidation: 4NH₃ + 5O₂ → 4NO + 6H₂O (Ostwald process for HNO₃)

Uses of Ammonia

• Fertiliser: urea (NH₂CONH₂), ammonium nitrate, ammonium sulphate — all nitrogen-rich fertilisers
• Nitric acid (HNO₃): via Ostwald process; used in explosives, fertilisers, dyes
• Cleaning agents: dilute ammonium hydroxide solution; removes grease; household cleaners

Nitrogen Cycle Connection

• Atmospheric N₂ cannot be used by most organisms; must be fixed (converted to usable form)
• Nitrogen fixation: Rhizobium bacteria in legume root nodules; lightning (N₂ + O₂ → 2NO); Haber process (industrial)
• Denitrification: Pseudomonas bacteria; return fixed nitrogen back to atmosphere as N₂

ICSE Exam Questions

• Haber process: state conditions (temperature, pressure, catalyst); explain why conditions chosen
• Lab preparation: equation, collection (upward displacement; NH₃ lighter than air), drying (CaO not P₂O₅)
• Properties test: wet red litmus paper turns blue; dense white fumes with HCl — both used in identification