When sodium sulphate solution is mixed with barium chloride solution, a white precipitate of barium sulphate is formed. Name the type of chemical reaction involved and give one reason for your answer.
Generated by claude-sonnet-4-6 · 2026-06-26 00:53 · grounding rag
Model Answer
The reaction involved is a double displacement reaction (also called a precipitation reaction).
Reason: The sulphate ions (SO₄²⁻) from sodium sulphate and barium ions (Ba²⁺) from barium chloride exchange (displace) each other to form an insoluble white precipitate of barium sulphate.
$$\text{Na}_2\text{SO}_4(aq) + \text{BaCl}_2(aq) \rightarrow \text{BaSO}_4(s) + 2\text{NaCl}(aq)$$
Source: Chapter 1, Section 1.2.4 Double Displacement Reaction
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Explanation
- Name of reaction (1 mark): Double displacement reaction. You may also call it a precipitation reaction — both are acceptable.
- Reason (1 mark): Examiners want you to mention exchange of ions between the reactants and/or the formation of an insoluble precipitate (BaSO₄). Either point earns the mark; stating both makes your answer complete.
- Writing the balanced equation supports your answer but is not always compulsory for 2 marks — include it to be safe.
- Remember: in double displacement, two compounds swap their ionic partners; neither element changes its oxidation state (unlike displacement or redox reactions).