# A galvanic cell which makes use of the following reaction at 298K. $Cr_2O_7^{2-}+14H^++6Fe^{2+}\rightarrow 2Cr^{3+}+6Fe^{3+}+7H_2O$.Given : $E^{\large\circ}(Cr_2O_7^{2-},H^+,Cr^{3+}|Pt)=1.33V;E^{\large\circ}(Fe^{3+},Fe^{2+}|Pt)=0.77V$.The contribution made to the standard emf of the cell by oxidation half-cell is

$\begin{array}{1 1}0.77V\\-0.77V\\1.33V\\-1.33V\end{array}$

In the reaction $Fe^{2+}$ is oxidised to $Fe^{3+}$.Hence,contribution made to the standard emf of the cell is -0.77V.