Question

Given that the standard potentials (E^o) of Cu²⁺/Cu and Cu⁺/Cu are 0.34 V and 0.522 V respectively, the E^o of Cu²⁺/Cu⁺ :

• A. - 0.182 V
• B. - 0.158 V
• C. 0.182 V
• D. +0.158 V

Hint:

Electrode potentials are not additive but free energies are: use \(\Delta G = -nFE\) for the three half reactions.

Answer 1

The Correct Option is D

Cu²⁺ + 2e^- \( o\) Cu, \(E^o = 0.34\) V, \(\Delta G_1 = -2F(0.34) = -0.68F\)
Cu⁺ + e^- \( o\) Cu, \(E^o = 0.522\) V, \(\Delta G_2 = -F(0.522) = -0.522F\)
Required: Cu²⁺ + e^- \( o\) Cu⁺ = (first) - (second).
\(\Delta G_3 = \Delta G_1 - \Delta G_2 = -0.68F + 0.522F = -0.158F\)
\(E^o = -\Delta G_3/(1\cdot F) = +0.158\) V.
Answer: (D) +0.158 V