When iron nails are placed in copper sulphate solution, the blue colour of the solution fades and a brown dep…

Question

When iron nails are placed in copper sulphate solution, the blue colour of the solution fades and a brown deposit forms on the nails. Using the concept of redox reactions, explain the chemical changes responsible for (i) the colour change in the solution and (ii) the deposit on the nail. Write the balanced chemical equation for the reaction and identify which substance is oxidised and which is reduced.

Accepted Answer

## Model Answer When iron nails are placed in copper sulphate solution, iron displaces copper because iron is more reactive than copper. **(i) Colour change:** Cu²⁺ ions (which give the blue colour) are removed from the solution and replaced by Fe²⁺ ions (forming light green FeSO₄). Hence, the blue colour fades. **(ii) Brown deposit:** Copper metal is deposited on the iron nails, forming the brown coating. **Balanced equation:** $$	ext{Fe}(s) + 	ext{CuSO}_4(aq) ightarrow 	ext{FeSO}_4(aq) + 	ext{Cu}(s)$$ **Redox identification:** - **Iron (Fe) is oxidised** — it loses electrons (Fe → Fe²⁺). - **Copper (Cu²⁺) is reduced** — it gains electrons (Cu²⁺ → Cu). Source: Chapter 1, Section 1.2.3 Displacement Reaction --- ## Explanation Examiners award marks for: (1) correct balanced equation, (2) explanation of colour change linking Cu²⁺ removal, and (3) correct identification of oxidised and reduced substances. Always state *why* something is oxidised/reduced (loss/gain of electrons). Th…

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