Question

The reduction potential $\left(E^0\right.$, in $\left.V \right)$ of $MnO _4^{-}( aq ) / Mn ( s )$ is ___
$\left[\right.$ Given : $\left.E_{\left( MnO _4( aq ) / MnO _2( s )\right)}^0=1.68 V ; E_{\left( MnO _2( s )/ Mn ^{2+}( aq )\right)}^0=1.21 V ; E_{\left( Mn ^2( aq ) / Mn ( s )\right)}^0=-1.03 V \right]$

Answer 1

For the required reaction $\Delta G ^{\circ}=\Delta G ^{\circ}+\Delta G _2^{\circ}+\Delta G ^{\circ}$
$ \Rightarrow 7 \times E =1.68 \times 3+1.21 \times 2+(-1.03) \times 2$
$ E =\frac{5.4}{7}=0.7714$