Question

$MnO_{4}^{2 -}\left(\right.1mole\left.\right)$ in neutral aqueous medium disproportionates to :

• A. $2/3$ mole $MnO_{4}^{-}$ and $1/3$ mole $MnO_{2}$
• B. $1/3$ mole $MnO_{4}^{-}$ and $2/3$ mole $MnO_{2}$
• C. $1/3$ mole $Mn_{2}O_{7}$ and $2/3$ mole $MnO_{2}$
• D. $2/3$ mole $Mn_{2}O_{7}$ and $1/3$ mole $MnO_{2}$

Answer 1

Answer: (A)

$MnO_{4}^{2 -}$ ( $1$ mole) in neutral aqueous medium will disproportionate to produce $2/3$ moles of $MnO_{4}^{-}$ and $1/3$ moles of $MnO_{2}$ .
$3K_{2}MnO_{4}+2H_{2}O \rightarrow 2KMnO4+MnO_{2}+4KOH$
Three moles of $K_{2}MnO_{4}$ gives two moles of $KMnO_{4}$ and one mole of $\text{MnO}_{2}$
So one mole of $K_{2}MnO_{4}$ will yield $\frac{2}{3}$ moles of $KMnO_{4}$ and $\frac{1}{3}$ mole of $\text{MnO}_{2}$