Question

The formula mass of Mohr's salt is 392 . The iron present in it is oxidised by $KMnO _{4}$ 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 $\left( NH _{4}\right)_{2} SO _{4} \cdot FeSO _{4} \cdot 6 H _{2} O$.
The equation is :
$5 Fe ^{2+}+ MnO _{4}^{-}+8 H ^{+} \longrightarrow$
$5 Fe ^{3+}+ Mn ^{2+}+4 H _{2} O$
Total change in oxidation number of iron
$=(+3)-(+2)$
$=+1$
So, equivalent wt. of Mohr's salt
$=\frac{\text { Mol. wt. of Mohr' s salt }}{1}$
$=\frac{392}{1}$