Question

EMF diagram for iron is given as:
$\underset{(Fe = +6)}{E ^{\circ}\text{(volts)}FeO _{4}^{2-}} \xrightarrow{+2.20} \underset{(Fe = +3)}{Fe ^{3+}} \xrightarrow{+0.77} \underset{(Fe = +2)}{Fe ^{2+}} \xrightarrow{-0.445} \underset{(Fe = +0)}{Fe ^{0}}$
Determine the value of $E _{ FeO _{4}^{2-} / Fe ^{2+}}^{\circ}$

Answer 1

$\Delta G _{3}{ }^{\circ}=\Delta G _{1}{ }^{\circ}+\Delta G _{2}{ }^{\circ}$
$- n \times F \times E _{3}^{\circ}=-3 \times F \times 2.20-1 \times F \times 0.77$
$-4 \times E _{0}^{\circ}=-6.60-0.77$
$E ^{\circ}=\frac{7.37}{4}=1.84$
$E ^{\circ}=+1.84$