Question

A solution of copper sulphate cannot be stored in a zinc vessel because

• A. Copper is more reactive than zinc
• B. Reduction potential of copper is less than zinc
• C. Oxidation potential of copper is higher than zinc
• D. Reduction potential of copper is higher than zinc

Hint:

Key Exam Tip:
The reactivity of metals in displacement reactions is determined by their standard electrode potentials. A metal with a lower (more negative) reduction potential is more reactive and will displace metals with higher reduction potentials from their salt solutions.

Answer 1

The Correct Option is D

This question pertains to the reactivity of metals and their behavior in electrochemical reactions, specifically displacement reactions. The relative reactivity of metals can be determined by their standard electrode potentials. A metal's standard reduction potential ($E^\circ$) indicates its tendency to gain electrons and be reduced. The standard reduction potentials for zinc and copper are:
• Zn$^{2+}$(aq) + 2e$^-$ $\rightarrow$ Zn(s), $E^\circ = -0.76$ V
• Cu$^{2+}$(aq) + 2e$^-$ $\rightarrow$ Cu(s), $E^\circ = +0.34$ V A more reactive metal has a lower (more negative) reduction potential, meaning it has a greater tendency to be oxidized (lose electrons). Conversely, a less reactive metal has a higher (more positive) reduction potential, meaning its ions have a greater tendency to be reduced. Let's analyze the options:
• (a) Copper is more reactive than zinc: This is incorrect. Zinc has a lower reduction potential (-0.76 V) than copper (+0.34 V), signifying that zinc is more reactive and readily oxidized.
• (b) Reduction potential of copper is less than zinc: This statement is factually incorrect. The reduction potential of copper (+0.34 V) is greater than that of zinc (-0.76 V).
• (c) Oxidation potential of copper is higher than zinc: The oxidation potential is the negative of the reduction potential. For copper, it's -0.34 V. For zinc, it's +0.76 V. Thus, the oxidation potential of copper is lower than that of zinc. This statement is incorrect.
• (d) Reduction potential of copper is higher than zinc: This statement is correct ($+0.34 \text{ V} > -0.76 \text{ V}$). The reason a copper sulphate solution cannot be stored in a zinc vessel is due to the electrochemical reactivity difference. Since zinc has a lower reduction potential (is more reactive), it will spontaneously displace copper ions from the copper sulphate solution. The reaction is: Zn(s) + Cu$^{2+}$(aq) $\rightarrow$ Zn$^{2+}$(aq) + Cu(s) This reaction consumes the zinc vessel and forms solid copper. The standard cell potential for this reaction is $E_{\text{cell}} = E^\circ_{\text{cathode}} - E^\circ_{\text{anode}} = +0.34 \text{ V} - (-0.76 \text{ V}) = +1.10 \text{ V}$. A positive cell potential confirms the spontaneity of the reaction. Therefore, option (d) correctly states the electrochemical basis for why zinc is more reactive than copper and will react with copper sulphate solution. Final Answer: \(\boxed{d}\)