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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.

Updated On: Jan 20, 2026
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Solution and Explanation

Excess chlorine Cl2 in drinking water is removed by treating it with sulphur dioxide SO2 in the presence of water. In this redox change:

  • Chlorine is reduced from 0 in Cl2 to -1 in Cl^-.
  • Sulphur is oxidised from +4 in SO2 to +6 in SO4^{2-}.

Balanced Redox Equation (in Aqueous Medium)

Cl2_{(aq)} + SO2_{(aq)} + 2H2O_{(l)} -> 2Cl^-_{(aq)} + SO4^{2-}_{(aq)} + 4H^+_{(aq)}

In words: Chlorine reacts with sulphur dioxide in water to form chloride ions, sulfate ions and hydrogen ions.

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