Question

The formula mass of Mohr's salt is 392 . The iron present in it is oxidised by $KMn{O}_4$ in acid medium. The equivalent mass of Mohr's salt is

• A. 392
• B. 31.6
• C. 278
• D. 156

Answer 1

Answer: (A)

Mohr's salt is ${\left(N{H}_4\right)}_{2}S{O}_4\cdot FeS{O}_4\cdot 6H_{2}O$.
The equation is :
$5F{e}^{2+}+Mn{O}_4^{-}+8H^{+}⟶$
$5F{e}^{3+}+M{n}^{2+}+4H_{2}O$
Total change in oxidation number of iron
$=(+3)-(+2)$
$=+1$
So, equivalent wt. of Mohr's salt
$=\frac{\text{ Mol. wt. of Mohr’ s salt }}{1}$
$=\frac{392}{1}$