Question

Given standard electrode potentials:

$F{e}^{3+}+3e^{-}\to Fe;E^0=-0.036V$

$F{e}^{2+}+2e^{-}\to Fe;E^0=-0.440V$

The standard electrode potential $E^o$ for $F{e}^{3+}+e^{-}\to F{e}^{2+}$ is:

• A. 0.476 V
• B. 0.404 V
• C. 0.40 V
• D. +0.772 V

Answer 1

The correct option is D +0.772 V

We know, $△G^{\circ }=-nF{E}^{\circ }$

$F{e}^{2+}+2e^{-}\to Fe$

$△G^{\circ }=-2\times F\times (-0.440V)=0.880F$ ...... (1)

$F{e}^{3+}+3e^{-}\to Fe$

$△G^{\circ }=-3\times F\times (-0.036)$ $=0.108F$----------(2)

On subtracting Eqs. (1) from (2)$,F{e}^{3+}+e^{-}\to F{e}^{2+}$

$△G^{\circ }=0.108F-0.880F=-0.772F$

$\Delta G^o=-nF{E}^o$

$E^{\circ }=\frac{△G^{\circ }}{-nF}=\frac{-0.772F}{-1\times F}=+0.772V$

Hence, the correct option is $D$.