At 298 K, a 1 litre solution containing 10 mmol of $\mathrm{C{r_2}O_7^{2 - }}$ and 100 mmol of $\mathrm{Cr^{3+}}$ shows a pH of 3.0.

Given : $\mathrm{C{r_2}O_7^{2 - } \to C{r^{3 + }}\,;\,E^\circ = 1.330}$V

and $\mathrm{{{2.303\,RT} \over F} = 0.059}$ V

The potential for the half cell reaction is $x\times10^{-3}$ V. The value of $x$ is __________