Science (086) — AI-generated practice question

This reaction is a double displacement reaction (also called a precipitation reaction).

When sodium sulphate solution is mixed with barium chloride solution, the ions exchange between the two reactants. The sulphate ions (SO₄²⁻) and barium ions (Ba²⁺) combine to form an insoluble white precipitate of barium sulphate (BaSO₄), while sodium chloride remains in solution.

$$\text{Na}_2\text{SO}_4(aq) + \text{BaCl}_2(aq) \rightarrow \text{BaSO}_4(s) + 2\text{NaCl}(aq)$$

The insoluble solid formed is called a precipitate, and any reaction that produces a precipitate is called a precipitation reaction. Since there is an exchange of ions between the reactants, it is a double displacement reaction.

Source: Chapter 1, Section 1.2.4 Double Displacement Reaction

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• 3 marks are typically split as: (1) correct name of reaction type, (1) reason/explanation of ion exchange, (1) correct balanced equation.
• Always write the balanced chemical equation with state symbols — examiners specifically look for (s), (aq) etc.
• Mention both names — "double displacement" AND "precipitation reaction" — to be safe, as either may be the expected answer.
• The key distinguishing feature of a double displacement reaction is exchange of ions between the two reactants.