Question

When potassium permanganate is titrated against ferrous ammonium sulphate, the equivalent weight of potassium permanganate is:

• A. molecular weight $/10$
• B. molecular weight $/5$
• C. molecular weight $/2$
• D. molecular weight

Answer 1

The correct option is B molecular weight $/5$

When pottasium permanganate$\left(KMn{O}_4\right)$ reacted with ferrous amonium sulphate or (Mohr's salt) $(FeS{O}_4.(N{H}_4{)}_{2}S{O}_4.6H_{2}O)$ then $KMn{O}_4$ will oxidise $F{e}^{+}2$ to $F{e}^{+}3$ and itself reduces $M{n}^{+}7$ to $M{n}^{+}2$.

So N factor of Mohr's salt is 5..

$Equivalent$ $weight$ $=$ $molecular$ $weight/Nfactor$

so equivalent weight of mohr's salt is molecular weight / 5.