Question

$Mn^{3 +}$ions are unstable in solution and undergo disproportionation to give $Mn^{2 +},MnO_{2}$and $H^{+}$ions. what will be the balanced equation for the reaction?

• A. $3Mn^{3 +} + 4H_{2}O \rightarrow MnO_{2} + Mn^{2 +} + 8H^{+}$
• B. $Mn^{3 +} + 4H_{2}O \rightarrow MnO_{2} + 4H^{+}$
• C. $Mn + 2H_{2}O \rightarrow MnO_{2} + 4H^{+}$
• D. $2Mn^{3 +} + 2H_{2}O \rightarrow MnO_{2} + Mn^{2 +} + 4H^{+}$

Answer 1

Answer: (D)

$2Mn^{3 +} + 2H_{2}O \rightarrow MnO_{2} + Mn^{2 +} + 4H^{+}$

Answer 2

: Skeletal equation is

$Mn^{3 +} \rightarrow Mn^{2 +} + MnO_{2} + H^{+}$ (gSA)

Oxidation half equation: $Mn^{3 +} \rightarrow \overset{+ 4}{MnO_{2}}$

or $Mn^{3 +} + 2H_{2}O \rightarrow MnO_{2} + 4H^{+} + e^{-}$ ….(i)

Reduction half equation: $Mn^{3 +} \rightarrow Mn^{2 +}$

or $Mn^{3 +} + e^{-} \rightarrow Mn^{2 +}$ …..(ii)

Adding eq. (i) and (ii) the balanced equation is

$2Mn^{3 +} + 2H_{2}O \rightarrow MnO_{2} + Mn^{2 +} + 4H^{+}$