Electrochemistry 2 Question 24
23. The standard reduction potentials of $\mathrm{Cu}^{2+} / \mathrm{Cu}$ and $\mathrm{Cu}^{2+} / \mathrm{Cu}^{+}$are $0.337 \mathrm{~V}$ and $0.153 \mathrm{~V}$ respectively. The standard electrode potential of $\mathrm{Cu}^{+} / \mathrm{Cu}$ half-cell is
(1997, 1M)
(a) $0.184 \mathrm{~V}$
(b) $0.827 \mathrm{~V}$
(c) $0.521 \mathrm{~V}$
(d) $0.490 \mathrm{~V}$
Numerical Value Based Question
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Solution:
- $E^{\circ}$ is an intensive property :
(i) $\mathrm{Cu}^{2+}+2 e^{-} \xrightarrow{E^{\circ}} \Delta G^{\circ}=-n E^{\circ} \mathrm{F} \quad \mathrm{Cu} \quad 0.337 \mathrm{~V} \quad-0.674 \mathrm{~F}$
(ii) $\mathrm{Cu}^{2+}+e^{-} \longrightarrow \mathrm{Cu}^{+} \quad 0.153 \mathrm{~V} \quad-0.153 \mathrm{~F}$
Subtracting (ii) from (i) gives :
$$ \begin{aligned} & \mathrm{Cu}^{+}+e^{-} & \longrightarrow \mathrm{Cu} \quad \Delta G^{\circ}=-0.521 \mathrm{~F}=-n E^{\circ} \mathrm{F} \ \Rightarrow & & E^{\circ}=0.521 \mathrm{~V} \ \because & n & =1 \end{aligned} $$
