Q55 / 180 · AIIMS 2015 · Chemistry

Assertion : Zinc displaces copper from copper sulphate solution. Reason : The $E_{298 \mathrm{~K}}^{\circ}$ of $\mathrm{Zn}$ is $-0.76 \mathrm{~V}$ and that of $\mathrm{Cu}$ is $+0.34 \mathrm{~V}$.

  • Correct answer
    A
    If both assertion and reason are true and reason is the correct explanation of assertion.
  • B
    Ifboth assertion and reason are true but reason is not the correct explanation of assertion.
  • C
    If assertion is true but reason is false.
  • D
    If both assertion and reason are false.

Solution

$$ \begin{aligned} & : \mathrm{Zn}_{(s)}+\mathrm{Cu}_{(a q)}^{2+} \rightarrow \mathrm{Zn}_{(a q)}^{2+}+\mathrm{Cu}_{(s)} \\ & \quad E_{\mathrm{Cu}^{2+} / \mathrm{Cu}}^{\mathrm{o}}=0.34 \mathrm{~V}, E_{\mathrm{Zn}^{2+} / \mathrm{Zn}}=-0.76 \mathrm{~V} \end{aligned} $$ Higher reduction potential of $\mathrm{Cu}^{2+}$ ion than $\mathrm{Zn}^{2+}$ ion shows that $\mathrm{Cu}^{2+}$ ion has more tendency to undergo reduction.

Hence, the correct answer is option: 'A'.

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