Chlorine is used to purify drinking water. Excess of chlorine is harmful. The excess chlorine is removed by treating with sulphur dioxide. Present a balanced equation for the reaction for this redox change taking place in water.

Explanation

The skeletal equation is:
`Cl_(2(aq)) + SO_(2(aq)) + H_(2)O_((l)) rarr Cl_((aq))^(-) + S0_(4(aq))^(2-)`
Reduction half equation:
`Cl_(2(aq)) rarr Cl_((aq))^(-)`
Balance Cl atoms,
`Cl_(2(aq))rarr2Cl_((aq))^(-)`
Balance O.N. by adding electrons
`Cl_(2(aq))+2e^(-)rarr2Cl_((aq))^(-)`
Oxidation half equation:
`SO_(2(aq))rarrSAO_(4(aq))^(2-)`
Balance O.N. by adding electrons
`SO_(2(aq)) rarr SO_(4(aq))^(2-) + 2e^(-)`
Balance charge by adding 4`H^(+)` ions:
`SO_(2( aq))rarr SO_(4(aq))^(2-) + 4H_((aq))^(+)+2e^(-)`
Balance O atoms by adding `2H_(2)O`,
`SO_(2(aq)) + 2H_(2)O_((l)) rarr SO_(4(aq))^(2-)+4H_((aq))^(+) + 2e^(-)`
Adding equation (1) and (2), we have,
`Cl_(2(aq))+SO_(2(aq))+2H_(2)O_((l)) rarr 2Cl_((aq))^(-)+SO_(4(aq))^(2-)+ 4H_((aq))^(+) `
This represents the balanced redox reaction.