Unit 17: Modern Chemical Manufactures
Class 11 Chemistry - Nepal Curriculum
Teaching Hours: 11
1. Introduction
This unit deals with modern chemical manufacturing processes used in industries. It includes principles and flow sheet diagrams of some widely used processes.
2. Manufacture of Ammonia – Haber’s Process
Principle: Ammonia is synthesized from nitrogen and hydrogen in the presence of an iron catalyst under high temperature and pressure.
N₂ + 3H₂ ⇌ 2NH₃ + Heat (Reversible and exothermic reaction)
- Temperature: 450–500°C
- Pressure: 200–300 atm
- Catalyst: Finely divided iron with promoters (Al₂O₃, K₂O)
Fig: Flow Sheet Diagram of Haber’s Process
3. Manufacture of Nitric Acid – Ostwald’s Process
Principle: Nitric acid is prepared by catalytic oxidation of ammonia to nitric oxide, followed by oxidation to nitrogen dioxide and then absorption in water.
4NH₃ + 5O₂ → 4NO + 6H₂O(Pt catalyst at 800°C)2NO + O₂ → 2NO₂3NO₂ + H₂O → 2HNO₃ + NO
Fig: Flow Sheet Diagram of Ostwald’s Process
4. Manufacture of Sulphuric Acid – Contact Process
Principle: Sulphur dioxide is oxidized to sulphur trioxide, which is then absorbed in concentrated H₂SO₄ to form oleum. Oleum is diluted to get sulphuric acid.
S + O₂ → SO₂2SO₂ + O₂ ⇌ 2SO₃(V₂O₅ catalyst, 450°C)SO₃ + H₂SO₄ → H₂S₂O₇H₂S₂O₇ + H₂O → 2H₂SO₄
Fig: Flow Sheet Diagram of Contact Process
5. Manufacture of Sodium Hydroxide – Diaphragm Cell
Principle: Electrolysis of brine (NaCl solution) using a diaphragm cell separates NaOH, chlorine, and hydrogen gas.
- At anode:
2Cl⁻ → Cl₂ + 2e⁻ - At cathode:
2H₂O + 2e⁻ → H₂ + 2OH⁻ - Net:
2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂
Fig: Flow Sheet Diagram of Diaphragm Cell Process
6. Manufacture of Sodium Carbonate – Solvay Process (Ammonia Soda)
Principle: Sodium carbonate is prepared using ammonia, carbon dioxide, water, and sodium chloride.
- NH₃ + CO₂ + H₂O + NaCl → NaHCO₃ ↓
- 2NaHCO₃ → Na₂CO₃ + CO₂ + H₂O (on heating)
- NH₃ is recovered and reused in the process.
Fig: Flow Sheet Diagram of Solvay Process
7. Fertilizers
Chemical fertilizers are industrially manufactured substances used to supply essential nutrients (N, P, K) to plants to enhance growth and yield.
A. Types of Chemical Fertilizers
- Nitrogenous Fertilizers: Urea, ammonium nitrate, ammonium sulphate
- Phosphatic Fertilizers: Superphosphate, triple superphosphate
- Potassic Fertilizers: Potassium chloride, potassium sulphate
B. Production of Urea
Principle: Urea is produced by the reaction of ammonia and carbon dioxide under high temperature and pressure.
2NH₃ + CO₂ ⇌ NH₂COONH₄(ammonium carbamate)NH₂COONH₄ → CO(NH₂)₂ + H₂O(urea)
Fig: Flow Sheet Diagram of Urea Production