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

Solution :
The following reaction occurs:
$$6F{e^{2 + }} + C{r_2}O_7^{2 - } + 14{H^ + } \to 6F{e^{3 + }} + 2C{r^{3 + }} + 7{H_2}O$$
From the above equation, we find that Mohr's salt  $$\left( {FeS{O_4}.{{\left( {N{H_4}} \right)}_2}S{O_4}.6{H_2}O} \right)$$      and dichromate reacts in 6 : 1 molar ratio.