Q1. [1] straightforward exam-ready
Which of the following is a precipitation reaction?
(A) CaO + H₂O → Ca(OH)₂
(B) 2Mg + O₂ → 2MgO
(C) Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCl(aq)
(D) Fe + CuSO₄ → FeSO₄ + Cu
- A CaO + H₂O → Ca(OH)₂
- B 2Mg + O₂ → 2MgO
- C Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCl(aq)
- D Fe + CuSO₄ → FeSO₄ + Cu
Generated by claude-sonnet-4-6 · 2026-06-26 00:53 · grounding rag
Model Answer
(C) Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCl(aq)
This is a precipitation reaction because an insoluble white precipitate of BaSO₄ is formed when two aqueous solutions are mixed.
Source: Chapter 1, Section 1.2.4 Double Displacement Reaction
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Explanation
- A precipitation reaction produces an insoluble solid (precipitate) from two aqueous solutions. The (s) symbol after BaSO₄ is the key indicator in the equation.
- Option A is a combination reaction; B is a combination/oxidation reaction; D is a displacement reaction.
- Examiners expect you to identify the precipitate (BaSO₄) as the reason for your choice.