JEE Main 2023 · 15 April · morning · Single correct · +4 / −1
Which one of the following is not an example of calcination?
- (a) CaCO₃ · MgCO₃ →(Δ) CaO+MgO+2 CO₂
- (b) 2 PbS+3 O₂ →(Δ) 2 PbO+2 SO₂
- (c) CaCO₃ →(Δ) CaO+CO₂
- (d) Fe₂ O₃ · xH₂ O →(Δ) Fe₂ O₃+xH₂ O
Answer and solution
Answer (b) 2 PbS+3 O₂ →(Δ) 2 PbO+2 SO₂
Solution
Chemistry ma’am · 3 steps
Ask one question of each reaction: does the ore just break apart, or does it react with oxygen?
- Calcination. The ore is heated strongly in a limited supply of air or in its absence. It only decomposes, giving off CO₂ from carbonates or water from hydrated oxides, and no oxygen is taken in.
- Roasting. The ore, usually a sulphide, is heated in excess air. Oxygen reacts with it, so O₂ appears on the left and the sulphur leaves as SO₂.
Option Ore type Is O₂ a reactant? Process (a) dolomite, a carbonate no, CO₂ is lost calcination (b) galena, a sulphide yes, gives SO₂ roasting (c) limestone, a carbonate no, CO₂ is lost calcination (d) hydrated iron oxide no, water is lost calcination - So. Only (b) uses oxygen from the air, which makes it roasting and not calcination. The answer is (b).
The idea to keep. Carbonates and hydrated ores are calcined: heat alone drives out CO₂ or water. Sulphide ores are roasted: they react with O₂ and give SO₂.
Answer from the NTA final answer key. Solution by PrepWiser.