Question

Given standerd electrode potentials
$F{e}^{2+}+2e^{-}$ $⟶$ $Fe;E^o=-0.440V$
$F{e}^{3+}+3e^{-}$ $⟶$ $Fe;E^o=-0.036V$

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. +0.404 v
• D. +0.772 V

Answer 1

The correct option is D +0.772 V

$\Delta G^0=-n{E}^{0}F$

$F{e}^{2+}+2e^{-}\to Fe$ .... (i)

$\Delta G^o=-2\times F\times (-0.440V)=0.880F$

$F{e}^{3+}+3e^{-}\to Fe$ .....(ii)

$\Delta G^o=-3\times F\times (-0.036)=0.108F$

On subtracting equation (i) from (ii)

$F{e}^{3+}+e^{-}\to F{e}^{2+}$

$\Delta G^o=0.108F-0.880F=-0.772F$

$E^o$ for the reaction $=-\frac{\Delta G^o}{nF}$

$E^o=-\frac{(-0.772F)}{1\times F}=+0.772V$.