Question

The number of moles of $KMn{O}_4$ that will be needed to react completely with one mole of ferrous oxalate in acidic solution is

• A. 4/5
• B. 3/5
• C. 2/5
• D. 1

Answer 1

Answer: (B)

When $KMn{O}_4$ reacts with ferrous oxalate in acidic solution then the following reaction takes place.
$\stackrel{+7}{\mathrm{Mn}}{O}_4^{-}+\stackrel{+2}{\mathrm{Fe}}\stackrel{+3}{C_2}{O}_4⟶\stackrel{+2}{M{n}^{+2}}+\stackrel{+4}{2C{O}_2}+F{e}^{3+}$
Here, $M{n}^{7+}$ is reduced to $M{n}^{2+}(+7\to +2)$ and carbon is oxidised to $C{O}_2(+3\to +4)$ and $F{e}^{2+}$ is oxidised to $F{e}^{3+}(+2\to +3)$. Thus,

Reduction $M{n}^{7+}+5e^{-}⟶M{n}^{2+}\downarrow 5$
The balanced chemical equation is as

$\because 5$ moles of $Fe{C}_2{O}_4$ are oxidised by 3 moles of $KMn{O}_4$.
$\therefore 1$ mole of $Fe{C}_2{O}_4$ is oxidised by $\frac{3}{5}$ moles of $KMn{O}_4$.