A Levels Chemistry (9701)•9701/13/O/N/20
Explanation
SO₂ neutralization with Ca(OH)₂ forms CaSO₄ in aqueous solution
Steps:
- SO₂ dissolves in water, forming H₂SO₃, which acts as a weak acid.
- In aqueous solution with dissolved oxygen, H₂SO₃ oxidizes to H₂SO₄.
- H₂SO₄ reacts with Ca(OH)₂ via neutralization: H₂SO₄ + Ca(OH)₂ → CaSO₄ + 2H₂O.
- CaSO₄ precipitates as the main initial solid product.
Why C is correct:
- CaSO₄ forms directly from the oxidation and acid-base reaction, per standard flue gas desulfurization chemistry.
Why the others are wrong:
- A. Ca(SO₃)₂ uses incorrect formula (calcium sulfite is CaSO₃) and represents unstable intermediate.
- B. CaS forms from H₂S reactions, not SO₂.
- D. SO₃ is a gaseous intermediate in SO₂ oxidation but not a product here.
Final answer: C
Topic: Group 2
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