Question

Given standard electrode potentials:
$Fe^{3+} + 3e^{-} \to Fe;\,\,\, E^{o} = -0.036$ volt
$Fe^{2+} + 2e^{-} \to Fe;\,\,\, E^{o} = -0.440$ volt
The standard electrode potential $E^{o}$ for
$Fe^{3+} + e^{-} \to Fe^{2+}$

• A. $-0.476$ volt
• B. $-0.404$ volt
• C. $0.440$ volt
• D. $0.772$ volt

Answer 1

Answer: (D)

$Fe^{3+} + 3 e \to Fe,\,\,\,\, E^{o}, = - 0.036$ volt; $\Delta G^{o}_{1}$
$Fe \to Fe^{2+} + 2e^{-},\,\,\,\, E^{o}_{2} = 0.44$ volt; $\Delta G^{o}_{2}$
$Fe^{3+} + e^{-} \to \Delta G^{o} = \Delta G^{o}_1 + \Delta G^{o}_{2}$
$-nFE^{o} = -3 FE^{o}_{1} + (-2FE^{o}_{2})$
$\Rightarrow -FE^{o} = -F(3E^{o}_{1} + 2E^{o}_{2})$
$E^{o} = (3 \times (0.036) + (2 \times 0.44)$
$E^{o} = 0.772$ volt