Question

Write the balanced equation.

$Mn{O}_4^{2-}\to {MnO}_4^{-}+Mn{O}_2$

• A. $3Mn{O}_4^{2-}+4H^{+}\to 2{MnO}_4^{-}+Mn{O}_2+2H_{2}O$
• B. $2Mn{O}_4^{2-}+2H^{+}\to 2{MnO}_4^{-}+Mn{O}_2+2H_{2}O$
• C. $3Mn{O}_4^{2-}+2H^{+}\to 2{MnO}_4^{-}+2Mn{O}_2+2H_{2}O$
• D. None of these

Answer 1

The correct option is A $3Mn{O}_4^{2-}+4H^{+}\to 2{MnO}_4^{-}+Mn{O}_2+2H_{2}O$

The unbalanced redox equation is as follows:

$Mn{O}_4^{2-}\to {MnO}_4^{-}+Mn{O}_2$

Balance all atoms other than H and O.

$2Mn{O}_4^{2-}\to {MnO}_4^{-}+Mn{O}_2$

The oxidation number of Mn changes from +6 (in $Mn{O}_4^{2-}$) to +7 (in ${MnO}_4^{-}$). The change in the oxidation number of Mn is 1.
The oxidation number of Mn changes from +6 (in $Mn{O}_4^{2-}$) to +4 (in $Mn{O}_2$). The change in the oxidation number of Mn is 2.

The increase in the oxidation number is balanced with decrease in the oxidation number by multiplying $Mn{O}_4^{2-}$ and ${MnO}_4^{-}$ with 2 for oxidation part.

$3Mn{O}_4^{2-}\to 2{MnO}_4^{-}+Mn{O}_2$

O atoms are balanced by adding 2 water molecules on RHS.

$3Mn{O}_4^{2-}\to 2{MnO}_4^{-}+Mn{O}_2+2H_{2}O$

Hydrogen atoms are balanced by adding 4 $H^{+}$ on LHS.

$3Mn{O}_4^{2-}+4H^{+}\to 2{MnO}_4^{-}+Mn{O}_2+2H_{2}O$
This is the balanced chemical equation.