JEE Main 2021 · 20 July · evening · Single correct · +4 / −1
Consider two chemical reactions (A) and (B) that take place during metallurgical process:
(A) ZnCO₃₍ₛ₎→(Δ) ZnO₍ₛ₎ + CO_(2(g))
(B) 2ZnS₍ₛ₎ + 3O_(2(g))→(Δ) 2ZnO₍ₛ₎ + 2SO_(2(g))
The correct option of names given to them respectively is :
- (a) (A) is calcination and (B) is roasting
- (b) Both (A) and (B) are producing same product so both are roasting
- (c) Both (A) and (B) are producing same product so both are calcination
- (d) (A) is roasting and (B) is calcination
Answer and solution
Answer (a) (A) is calcination and (B) is roasting
Solution
Chemistry ma’am · 3 steps
Do not look at the product, look at what goes in: was oxygen from the air needed or not?
- Calcination. Heating an ore strongly in a limited supply of air, or with no air at all. It suits carbonate and hydrated ores, which lose CO₂ or water on their own when heated.
- Roasting. Heating an ore strongly in excess air. It suits sulphide ores, because oxygen from the air must react with the ore to turn the sulphide into an oxide and release SO₂.
Reaction Ore type Is O₂ a reactant? Gas given off Process (A) ZnCO₃ → ZnO + CO₂ carbonate no CO₂ calcination (B) 2ZnS + 3O₂ → 2ZnO + 2SO₂ sulphide yes SO₂ roasting - So. (A) is calcination and (B) is roasting. Both give ZnO, but the ore you start from and the need for air decide the name, so the answer is (a).
The idea to keep. Carbonate or hydrated ore, heated without needing air: calcination. Sulphide ore, heated in excess air with O₂ reacting: roasting. The starting ore names the process, not the oxide you end up with.
Answer from the NTA final answer key. Solution by PrepWiser.