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

Explanation

Chlorinie reacts with sulplhur dioxide in the presence of water as followos :
`CI_(2)(aq)+SO_(2)(aq)+H_(2)O(l)rarrCI^(-)(aq)+SO_(4)^(2-)(aq)`
step I.Separation of equation in two half reaction
(i) write the O.N of each atom in the skeletion equation:
`overset(0)CI_(2)+overset(+4)Soverset(-2)O_(2)+overset(+1)H_(2)Orarr(overset(-1)CI)^(-)+(overset(+6)Soverset(-2)O_(4))^(2-)`
(ii) Identify the atoms which undergo change in O.N `overset(0)CI_(2)+overset(+4)S O_(2)+H_(2)Orarr(overset(-1)CI)^(-)+(overset(+6)SO_(4))^(2-)`
(iii) Find the species involved in the oxidation and reductionn half reactions

Step II Balancing oxidation half reaction
`overset(+4)S O_(2)rarroverset(+6)SO_(4)^(2-)+2e^(-)`
`SO_(2)rarrSO_(4)^(2-)+4H^(+)+2e^(-)`
`SO_(2)+2H_(2)OrarrSO_(4)^(2-)+4H^(+)+2e(-)`
Step III Balancing reduction half reaction
`CI_(2)+2e^(-)rarr2CI^(-)`
Adding the two balanced half freaction
`{:(SO_(2)+2H_(2)OrarrSO_(4)^(2-)4H^(+)+2e^(-)),(CI_(2)+2e^(-)rarr2CI^(-))/(SO_(2)+CI_(2)+2h_(2)OrarrSO_(4)^(2-)+4H^(+)+2CI^(-)):}`