Devise a cell for which the cell reaction is
\[
\mathrm{H}_{2} \mathrm{O}(\mathrm{l})=\mathrm{H}^{+}(\mathrm{ao})+\mathrm{OH}^{-}(\mathrm{ao})
\]
Calculate $\Delta_{\mathrm{r}} G^{\circ}$ at $25^{\circ} \mathrm{C}$ from electrode potentials. What is the value of the equilibrium constant at this temperature?