Study of Compounds — Ammonia
Introduction
Ammonia (NH₃) is a vital compound of nitrogen and hydrogen. In ICSE Class 10 Chemistry, you study its industrial manufacture by Haber's process, its characteristic basic nature, reducing properties, and diverse applications.
Haber's Process (Manufacture of Ammonia)
N₂(g) + 3H₂(g) ⇌ 2NH₃(g) + Heat
Conditions
| Parameter | Condition |
|---|---|
| Temperature | 450−500°C |
| Pressure | 200−300 atm |
| Catalyst | Finely divided iron with traces of Mo or Al₂O₃ (promoter) |
| Source of N₂ | Air (liquefied and separated) |
| Source of H₂ | Water gas or natural gas |
Key Points
- The reaction is reversible and exothermic.
- Le Chatelier's principle: high pressure favours NH₃ formation; moderate temperature is a compromise between yield and rate.
- Unreacted N₂ and H₂ are recycled for maximum efficiency.
Physical Properties
| Property | Observation |
|---|---|
| Colour | Colourless gas |
| Odour | Pungent, characteristic smell |
| Density | Lighter than air (VD = 8.5) |
| Solubility | Extremely soluble in water (~700 volumes in 1 volume of water) |
| Liquefaction | Easily liquefied by pressure (b.p. −33.4°C) |
Chemical Properties
Basic (Alkaline) Nature
NH₃(g) + H₂O ⇌ NH₄OH(aq) ⇌ NH₄⁺ + OH⁻
- Ammonia solution (NH₄OH) turns red litmus blue (weak base).
- Neutralises acids: NH₃ + HCl → NH₄Cl
Precipitation Reactions (with metal salts)
| Salt solution | Precipitate | Colour |
|---|---|---|
| FeCl₃ | Fe(OH)₃ | Reddish brown |
| CuSO₄ | Cu(OH)₂ (then dissolves in excess to give deep blue solution) | Pale blue |
| ZnSO₄ | Zn(OH)₂ (then dissolves in excess) | White |
Reducing Property
Ammonia acts as a reducing agent (N is in −3 oxidation state and can be oxidised).
With heated CuO:
2NH₃ + 3CuO → 3Cu + N₂ + 3H₂O
With chlorine (excess):
2NH₃ + 3Cl₂ → N₂ + 6HCl
With chlorine (limited):
NH₃ + 3Cl₂ → NCl₃ + 3HCl (explosive)
Uses of Ammonia
- Fertiliser manufacture (urea, ammonium sulphate, ammonium nitrate).
- Production of nitric acid (Ostwald's process).
- Refrigerant in ice plants and cold storage.
- Laboratory reagent (NH₄OH).
- Manufacture of explosives, dyes, and cleaning agents.
Comparison: NH₃ vs HCl
| Property | Ammonia (NH₃) | Hydrogen chloride (HCl) |
|---|---|---|
| Odour | Pungent, characteristic | Pungent, choking |
| Density | Lighter than air | Heavier than air |
| Aqueous solution | Alkaline (NH₄OH) | Acidic (HCl) |
| Reaction with each other | NH₃ + HCl → NH₄Cl (white fumes) | — |
Common Mistakes and Fixes
| Mistake | Fix |
|---|---|
| Thinking NH₃ is collected by upward delivery | NH₃ is lighter than air — collected by DOWNWARD delivery |
| Calling NH₃ a strong base | NH₃ is a WEAK base (NH₄OH partially dissociates) |
| Forgetting the catalyst in Haber's process | Fe catalyst with Mo or Al₂O₃ promoter |
| Confusing Haber's and Ostwald's processes | Haber: NH₃ from N₂+H₂; Ostwald: HNO₃ from NH₃ |
ICSE Exam Focus
This chapter carries 4–6 marks. Key topics: Haber's process conditions, basic nature, fountain experiment (similar to HCl), reducing property with CuO, uses.
Marks Blueprint: Haber's process — 2 marks, Basic/reducing properties — 2 marks, Uses — 1 mark.
Self-Test Questions
-
Describe Haber's process for the manufacture of ammonia. Write the reaction conditions.
-
Explain why ammonia is considered a reducing agent. Write its reaction with heated CuO.
-
What is observed when NH₃ is passed through CuSO₄ solution? Give equations.
-
Why is ammonia collected by downward displacement of air?
-
What is the fountain experiment for ammonia? How does it differ from the HCl fountain experiment?
-
State three important uses of ammonia.
