Read the following and answer the questions that follow:
Preeti observed that when she added a clean iron nail to a blue solution of copper sulphate, the solution gradually turned light green and a reddish-brown deposit appeared on the iron nail. Her teacher explained that a metal higher in the activity series displaces a metal lower down from its salt solution, and that this principle is used to compare the reactivity of metals.
(i) Write the balanced chemical equation for the reaction that occurred when the iron nail was placed in copper sulphate solution. Name the type of reaction. (1 mark)
(ii) Why did the blue colour of the copper sulphate solution fade and turn light green? (1 mark)
(iii) If Preeti places a copper wire in a solution of iron sulphate (FeSO₄), what will she observe? Give a reason based on the activity series. (1 mark)
(iv) Using the same principle of displacement, predict whether zinc can displace copper from copper sulphate solution. Write the balanced equation if the reaction occurs, or justify why it does not. (1 mark)
Generated by claude-sonnet-4-6 · 2026-06-26 01:06 · grounding rag
Model Answer
(i) $\text{Fe}(s) + \text{CuSO}_4(aq) \rightarrow \text{FeSO}_4(aq) + \text{Cu}(s)$
This is a displacement reaction (iron displaces copper from copper sulphate solution).
(ii) Iron reacts with blue copper sulphate to form green iron sulphate (FeSO₄). As Cu²⁺ ions are replaced by Fe²⁺ ions, the blue colour fades and turns light green.
(iii) No reaction will occur. Copper is lower than iron in the activity series, so copper cannot displace iron from iron sulphate solution. No change will be observed in the solution or on the copper wire.
(iv) Yes, zinc can displace copper because zinc is more reactive than copper (higher in the activity series). The reaction is:
$$\text{Zn}(s) + \text{CuSO}_4(aq) \rightarrow \text{ZnSO}_4(aq) + \text{Cu}(s)$$
Source: Chapter 1, Section 1.2.3 Displacement Reaction
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Explanation
- (i) The equation from the textbook (Eq. 1.24) is already balanced (1 Fe, 1 Cu, 1 S, 4 O on each side). Always name the reaction type.
- (ii) Focus on the ionic change: Cu²⁺ (blue) is replaced by Fe²⁺ (pale green). Examiners want both the chemical reason and the colour explanation.
- (iii) A common trap — students assume a reaction always occurs. The activity series rule works both ways: a less reactive metal cannot displace a more reactive one.
- (iv) Equation 1.25 from the textbook directly supports this. Zinc and lead are explicitly stated to be more reactive than copper.