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)

392

Answer 2

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 $=\frac{\text { Mol. } \text { wt. of Mohr's salt }}{1}=\frac{392}{1}=392$