Science (086) — AI-generated practice question

Displacement Reaction: A reaction in which a more reactive element displaces a less reactive element from its compound.

Example: Iron displaces copper from copper sulphate solution.

$$\text{Fe}(s) + \text{CuSO}_4(aq) \rightarrow \text{FeSO}_4(aq) + \text{Cu}(s)$$

Double Displacement Reaction: A reaction in which two different ions are exchanged between the reactants to form two new compounds.

Example: Sodium sulphate reacts with barium chloride to form a 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, Sections 1.2.3 and 1.2.4

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• 3 marks split: ~1 mark for each definition + example + equation (examiners often award ½ mark for definition, ½ for equation per reaction type).
• The key distinction: in displacement, one element pushes out another; in double displacement, two ions exchange between compounds.
• Always balance the equations — unbalanced equations lose marks.
• The BaSO₄ precipitate (white, insoluble) is a classic double displacement / precipitation example straight from the textbook Activity 1.10.