When iron nails are dipped in copper sulphate solution, certain changes are observed after some time. (i) State the two observations you would expect in this experiment and write a balanced chemical equation for the reaction. (ii) Identify the type of chemical reaction and explain what property of metals determines whether one metal can displace another from its salt solution. (iii) Identify the substance oxidised and the substance reduced in this reaction, giving a reason for each in terms of gain or loss of electrons (or change in the nature of the compound).
Generated by claude-sonnet-4-6 · 2026-06-26 00:54 · grounding rag
Model Answer
(i) Observations and Equation:
- The iron nail acquires a brownish (reddish-brown) coating of copper on its surface.
- The blue colour of copper sulphate solution fades (becomes pale green due to formation of FeSO₄).
Balanced equation:
$$\text{Fe}(s) + \text{CuSO}_4(aq) \rightarrow \text{FeSO}_4(aq) + \text{Cu}(s)$$
(ii) Type of Reaction and Property Determining Displacement:
This is a displacement reaction — iron displaces copper from copper sulphate solution. The property that determines whether one metal can displace another is its reactivity (position in the activity series). A more reactive metal displaces a less reactive metal from its salt solution. Since iron is more reactive than copper (iron is above copper in the reactivity series), it displaces copper.
(iii) Oxidised and Reduced Substances:
- Iron (Fe) is oxidised — it loses electrons, changing from Fe (neutral metal) to Fe²⁺ in FeSO₄.
- Copper (Cu²⁺) is reduced — it gains electrons, changing from Cu²⁺ in CuSO₄ to Cu (neutral metal).
Source: Chapter 1, Section 1.2.3 (Displacement Reaction); Chapter 3, Section 3.2.4 & 3.2.5
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Explanation
- Part (i): Examiners expect both observations clearly — the colour change of the nail AND the fading of the blue colour. The equation must be balanced with state symbols.
- Part (ii): The key term is "reactivity series" / "activity series." Just saying "iron is more reactive" without linking it to the series/concept of reactivity will lose a mark.
- Part (iii): Always use the electron language — "loses electrons = oxidised," "gains electrons = reduced." Link it back to the specific species (Fe → Fe²⁺ and Cu²⁺ → Cu). This is the OIL RIG concept applied to the reaction.