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Question

Balance the following unbalanced equation (in acidic medium) by ion electron method (half reaction method). Mn _ ( aq ) ^ 2+ + ClO _ 3( qq ) ^ - MnO _ 2( s ) + ClO _ 2( aq )

Vidyadip · Accepted Answer

Step 1: Write imbalanced equation for the redox reaction. Assign oxidation number to all the atoms in reactants and products. Divide the equation into two half equations.

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Step 2: Balance the atoms except $O$ and $H$ in each half equation. Balance half equations for $O$ atoms by adding $H _2 O$ to the side with less $O$ atoms. $Add 2 H _2 O$ to left side of oxidation half equation and $1 H _2 O$ to the right side of reduction half equation.
Oxidation: $Mn _{(\text {aq) }}^{2+}+2 H _2 O _{(l)} \longrightarrow MnO _{2(s)}$
Reduction: $ClO _{3(\text { (aq) }}^{-} \longrightarrow ClO _{2(\text {(aq) }}+ H _2 O _{(f)}$

Step 3: Balance $H$ atoms by adding $H +$ ions to the side with less $H$. Hence add $4 H ^{+}$ ions to the right side of oxidation half equation and $2 H ^{+}$ions to the left side of reduction half equation.
Oxidation: $Mn _{(\text {(aq) }}^{2+}+2 H _2 O _{(l)} \longrightarrow MnO _2+4 H _{( aq )}^{+}$
Reduction: $ClO _{3( aq )}^{-}+2 H _{( aq )}^{+} \longrightarrow ClO _{2 \text { (aq) }}+ H _2 O _{(l)}$
Step 4: Now add 2 electrons to the right side of oxidation half equation and 1 electron to the left side of reduction half equation to balance the charges.
Oxidation: $Mn _{(\text {(aq) }}^{2+}+2 H _2 O _{(l)} \longrightarrow MnO _{2(s)}+4 H _{( aq )}^{+}+2 e ^{-}$
Reduction: $ClO _{3(\text { (aq) })}^{-}+2 H _{(\text {aq) }}^{+}+ e ^{-} \longrightarrow ClO _{2( aq )}+ H _2 O _{(l)}$
Step 5: Multiply reduction half equation by 2 to equalize number of electrons in two half equations. Then add two half equation.
Oxidation: $Mn _{( aq )}^{2+}+2 H _2 O _{(l)} \longrightarrow MnO _2+4 H _{( aq )}^{+}+2 e ^{-}$
Reduction: $2 ClO _{3(\text { (aq) }}^{-}+4 H _{(\text {aq) }}^{+}+2 e ^{-} \longrightarrow 2 ClO _{2(\text { (aq) }}+2 H _2 O _{(l)}$
Add two half equations:
$Mn _{( aq )}^{2+}+2 ClO _{3( aq )}^{-} \longrightarrow MnO _{2( s )}+2 ClO _{2( aq )}$
The equation is balanced in terms of number of atoms and the charges.
Hence, balanced equation: $Mn _{( aq )}^{2+}+2 ClO _{3( aq )}^{-} \longrightarrow MnO _{2( s )}+2 ClO _{2( aq )}$+

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