Given that the standard potential ($\mathrm{E}^{\circ}$) of $\mathrm{Cu}^{2+} / \mathrm{Cu}$ and $\mathrm{Cu}^{+} / \mathrm{Cu}$ are 0.34 V and 0.522 V respectively, the $\mathrm{E}^{\circ}$ of $\mathrm{Cu}^{2+} / \mathrm{Cu}^{+}$ is

JEE Main · 2020 · 07 Jan 2020 · Shift 1 · Redox Reactions and Electrochemistry

Given that the standard potential (

E^{\circ}

) of

Cu^{2 +} / Cu

and

Cu^{+} / Cu

are 0.34 V and 0.522 V respectively, the

E^{\circ}

Cu^{2 +} / Cu^{+}

Answer: (C)

Combine the half-reactions through their free energies, since potentials do not add directly when the electron counts differ. For

C u^{2 +} + 2 e^{-} \to Cu

Δ G = - 2 F (0.34)

, and for

C u^{+} + e^{-} \to Cu

Δ G = - 1 F (0.522)

. Subtracting gives

C u^{2 +} + e^{-} \to C u^{+}

with

Δ G = - F (2 \times 0.34 - 0.522)

, so

E^{\circ} = 2 \times 0.34 - 0.522 = + 0.158 V

JEE Main · 2020 · 07 Jan 2020 · Shift 1 · Single correct option