A student adds a piece of zinc to copper sulphate solution and observes that the blue colour of the solution gradually fades and a reddish-brown deposit forms on the zinc. (i) Write the balanced chemical equation for this reaction. (ii) Identify the type of reaction. (iii) What does this result tell you about the relative reactivities of zinc and copper?
Generated by claude-sonnet-4-6 · 2026-06-26 01:05 · grounding rag
Model Answer
(i) Balanced chemical equation:
$$\text{Zn}(s) + \text{CuSO}_4(aq) \rightarrow \text{ZnSO}_4(aq) + \text{Cu}(s)$$
(ii) Type of reaction:
This is a displacement reaction, as zinc displaces copper from copper sulphate solution.
(iii) Relative reactivities:
Zinc is more reactive than copper. A more reactive metal can displace a less reactive metal from its salt solution. Since zinc displaces copper from copper sulphate, zinc is higher than copper in the reactivity series.
Source: Chapter 1, Section 1.2.3 Displacement Reaction; Chapter 3, Section 3.2.4
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Explanation
- The equation (1.25) is directly given in the textbook — write it with state symbols for full marks.
- "Displacement reaction" is the exact NCERT term; do not write "single displacement" or "substitution."
- For part (iii), the key idea is: a more reactive metal displaces a less reactive one. The reactivity series (Table 3.2) places Zn above Cu, confirming this.
- The fading blue colour indicates CuSO₄ is being consumed; the reddish-brown deposit is metallic copper being formed — good details to mention if asked to describe observations.