What is the standard reduction potential ( E ^ o ) for Fe ^ 3 + →...

$\left(i\right){Fe}^{3 +} \to Fe$ ${E}_{1}^{o}$;

$' n '$ factor$= 3$

${\text{\Delta G}}_{1}^{∘} = - 3 \times F \times {E}_{1}^{o}$

\left(ii\right){Fe}^{3 +} + {e}^{-} \to {Fe}^{2 +}$${E}_{2}^{o}$; $0 . 77$

$' n '$ factor$= 1$

$∆ {G}_{2}^{∘} = - 1 \times F \times 0 . 77$

\left(iii\right){Fe}^{2 +} + 2{e}^{-} \to Fe{E}_{3}^{o} = - 0 . 47$<br /><br />$' n '$factor$= 2$<br /><br />$∆ {G}_{3}^{∘} = - 2 \times F \times - 0 . 47$<br /><br />${\Delta G}_{1} = {\Delta G}_{2} + {\Delta G}_{3}$<br /><br />$- 3{FE}_{{}^{1}}^{o} = \left(- 1 \times 0 .77 \times F\right) + \left(2 \times 0 .47 \times F\right)$<br /><br />${\text{-E}}_{{}^{1}}^{o} = \dfrac{\left[\left(2 \times 0 .47\right) + \left(- 0 .77\right)\right]F}{3F} = 0 .057 V$</p><p>${\text{E}}_{{}^{1}}^{o} = - 0 .057 V$