Question

$Cu ^{+}(a q)$ is unstable in solution and undergoes simultaneous oxidation and reduction according to the reaction $2 C u^{+}(a q) \rightleftharpoons C u^{2+}(a q)+C u(s)$ Choose the correct $E^{0}$ for above reaction if $E_{ Cu ^{2+}}^{0} / Cu ^{+}=0.34 V$ and $E_{ Cu ^{2+} / Cu ^{+}}^{0}=0.15\, V$

• A. - 0.38 V
• B. + 0.49 V
• C. + 0.38 V
• D. - 0.19 V

Answer 1

Answer: (C)

From given data (from $\left.\Delta G ^{0}=- nE ^{\circ} F \right)$
(i) $Cu ( s ) \longrightarrow Cu ^{2+}( aq )+2 e ^{-} \cdot \Delta G _{1}^{0}=-2 \times(-0.34) \times F$
(ii) $Cu ^{2+}( aq )+ e ^{-} \longrightarrow Cu ^{+}( aq ) \cdot \Delta G _{2}^{0}=-1 \times(0.15) F$
On adition
$Cu ( s ) \longrightarrow Cu ^{+}( aq )+ e ^{-} \cdot \Delta G _{3}^{0}=-1 \times E ^{0} \times E$
$\Delta G _{3}^{0}=\Delta G _{1}^{0}+\Delta G _{2}^{0}$
$=(-2 \times-0.34 \times F )+(-1 \times 0.15 \times F )$
$=+0.68 F -0.15 F -0.53\, F$
or $E ^{\circ}=-0.53 \,V$
Reaction,
$2 Cu ^{+}( aq ) \rightleftharpoons Cu ^{2+}( aq )+ Cu ( s ) E ^{\circ}=\text { ? }$
So, $Cu ^{+}( aq )+ e ^{-} \rightleftharpoons Cu ( s ), E ^{0}=+0.53 \,V$
$Cu ^{+}( aq ) \rightleftharpoons Cu ^{2+}( aq )+ e ^{-} ; E ^{0}=-0.15\, V$
$3 Cu ^{+}( aq ) \rightleftharpoons Cu ^{2+}( aq )+ Cu ( s ), E ^{0}=+0.38\, V$