Q1. [3] medium thorough-understanding
When iron nails are dipped in copper sulphate solution, the blue colour of the solution fades and the nails turn brownish. Write the balanced chemical equation for this reaction, name the type of reaction, and explain what causes these colour changes.
Generated by claude-sonnet-4-6 · 2026-06-07 16:43 · grounding rag
Model Answer
Balanced Chemical Equation:
$$\text{Fe}(s) + \text{CuSO}_4(aq) \rightarrow \text{FeSO}_4(aq) + \text{Cu}(s)$$
Type of Reaction: Displacement reaction — iron (more reactive) displaces copper from copper sulphate solution.
Explanation of colour changes:
- The blue colour fades because blue-coloured copper sulphate (CuSO₄) is consumed and replaced by light green ferrous sulphate (FeSO₄), which is pale/colourless in dilute solution.
- The nails turn brownish because copper metal is deposited on the surface of the iron nails.
Source: Chapter 1, Section 1.2.3 – Displacement Reaction
---
Explanation
- Examiners award 1 mark for the correct balanced equation with state symbols, 1 mark for naming the reaction type, and 1 mark for explaining both colour changes (blue fading + brownish nails).
- Make sure to mention why each colour change happens — it is not enough to just state that they change.
- The equation given in the textbook is already balanced (1 Fe, 1 Cu, 1 S, 4 O on each side), so no extra coefficients are needed.
- Key phrase to remember: "Iron displaces copper from copper sulphate solution" — this is the definition of a displacement reaction.