Q. 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
A) 3
B) 4
C) 5
D) 6
Explanation
(d)
$6Fe^{2 +} + Cr_{2}O_{7}^{2 -} + 14H^{+} \rightarrow 6Fe^{3 +} + 2Cr^{3 +} + 7H_{2}O$
$\begin{matrix}
+ 6 \\
Cr_{2}O_{7}^{2 -}
\end{matrix} \rightarrow Cr^{3 +}$
$x$-factor=6
Mohr’s salt, $FeSO_{4}.\left( NH_{4} \right)_{2}SO_{4}.6H_{2}O$
$oxidation;\ Fe^{2 +} \rightarrow Fe^{3 +}$
$x$-factor=1
Mole ratio is reverse of $x$-factor ratio. Therefore, one mole of dichromate required=6 moles of Mohr’s salt.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.