Question

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

• A. 4/5
• B. 2/5
• C. 1
• D. 3/5

Answer 1

Answer: (B)

$2KMn{O}_4+3H_{2}S{O}_4\to K_{2}S{O}_4+2MnS{O}_4$
$+3H_{2}O+5[O]$
$[Mn{O}_4^{-}+8H^{+}+5e^{-}\to M{n}^{2+}+4H_{2}O]\times 2$
$\frac{[S{O}_3^{2-}+H_{2}O\to S{O}_4^{2-}+2H^{+}+2e^{-}]\times 5}{2Mn{O}_4^{-}+6H^{+}+5S{O}_3^{2-}\to 2M{n}^{2+}+5S{O}_4^{2-}+3H_{2}O}$
$5$ moles of sulphite ions react with
= $2$ moles of $Mn{O}_4^{-}$
So, $1$ mole of sulphite ions react with
$=\frac{2}{5}molesofMn{O}_4^{-}$.