Question

Balance the following equation, when it occurs in basic medium.

${ClO}_3^{-}⟶C{l}^{-}$

• A. ${ClO}_3^{-}+3H_{2}O+6e\to C{l}^{-}+6O{H}^{-}$
• B. ${ClO}_3^{-}+3H_{2}O+5e\to C{l}^{-}+6O{H}^{-}$
• C. $3{ClO}_3^{-}+3H_{2}O+3e\to C{l}^{-}+3O{H}^{-}$
• D. None of these

Answer 1

The correct option is A ${ClO}_3^{-}+3H_{2}O+6e\to C{l}^{-}+6O{H}^{-}$

The unbalanced redox equation is as follows:
${ClO}_3^{-}\to C{l}^{-}$
O atoms are balanced by adding 3 water molecules on RHS.
${ClO}_3^{-}\to C{l}^{-}+3H_{2}O$

Hydrogen atoms are balanced by adding 6 $H^{+}$ ions on the LHS.
${ClO}_3^{-}+6H^{+}\to C{l}^{-}+3H_{2}O$

Balance the charges by adding 6 electrons on the LHS.
${ClO}_3^{-}+6H^{+}+6e^{-}\to C{l}^{-}+3H_{2}O$

Since, the reaction occurs in basic medium, add 6 hydroxide ions on both sides of the equation.
${ClO}_3^{-}+6H^{+}+6e^{-}+6O{H}^{-}\to C{l}^{-}+3H_{2}O+6O{H}^{-}$

On LHS, 6 $H^{+}$ ions combine with 6 $O{H}^{-}$ ions to form 6 water molecules out of which, 3 water molecules cancels with 3 water molecules on RHS.

${ClO}_3^{-}+3H_{2}O+6e^{-}\to C{l}^{-}+6O{H}^{-}$
This is the balanced chemical equation.