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  4. 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

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Q. 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

AFMCAFMC 2008

Solution:

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