Question

$Mn{O}_4^{2-}(1mole)$ in neutral aqueous medium disproportionates to :

• A. $2/3$ mole $Mn{O}_4^{-}$ and $1/3$ mole $Mn{O}_2$
• B. $1/3$ mole $Mn{O}_4^{-}$ and $2/3$ mole $Mn{O}_2$
• C. $1/3$ mole $M{n}_2{O}_7$ and $2/3$ mole $Mn{O}_2$
• D. $2/3$ mole $M{n}_2{O}_7$ and $1/3$ mole $Mn{O}_2$

Answer 1

Answer: (A)

$Mn{O}_4^{2-}$ ( $1$ mole) in neutral aqueous medium will disproportionate to produce $2/3$ moles of $Mn{O}_4^{-}$ and $1/3$ moles of $Mn{O}_2$ .
$3K_{2}Mn{O}_4+2H_{2}O\to 2KMnO4+Mn{O}_2+4KOH$
Three moles of $K_{2}Mn{O}_4$ gives two moles of $KMn{O}_4$ and one mole of ${\text{MnO}}_2$
So one mole of $K_{2}Mn{O}_4$ will yield $\frac{2}{3}$ moles of $KMn{O}_4$ and $\frac{1}{3}$ mole of ${\text{MnO}}_2$