Consider  titration of potassium dichromate solution with acidified Mohr's salt solution using diphenyl amine as indicator. The number of moles of Mohr's salt required per mole of dichromate is :

In the given titration, potassium dichromate $\left({\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7\right)$ oxidises ${\mathrm{Fe}}^{2+}$ of Mohr's salt : $(\left.{\text{FeSO}}_4{\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4 .6{\mathrm{H}}_2\mathrm{O}\right)$ solution. So, the reaction will be:

                                  ${\mathrm{Cr}}_2{\mathrm{O}}_7^{2-}+6{\mathrm{Fe}}^{2+}+14 {\mathrm{H}}^{+}\to 2{\mathrm{Cr}}^{3+}+6{\mathrm{Fe}}^{+3}+7{\mathrm{H}}_2\mathrm{O}$

no. of moles                  1                6

$\therefore$              no. of moles of Mohr's salt required per mole of

dichromate $\left({\mathrm{Cr}}_2{\mathrm{O}}_7^{2-}\right)$ is 6.