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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

8.23  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

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Base equation-  SO_{2}+Cl_{2}\rightarrow Cl^{-}+SO_{4}^{2-}--------------(have to remember)

Now we have to balance the oxidation half and reduction half.

oxidation halfSO_{2}\rightarrow SO_{4}^{2-}

balancing-  Oxygen is balanced by adding water molecule, Hydrogen is balanced by H^{+} ion and for charge add e^{-}(electron)SO_{2} +2H_{2}O\rightarrow SO_{4}^{2-}+4H^{+}+2e^{-}

Reduction hallfCl_{2}\rightarrow Cl^{-}

Balancing-  to balance charge add an electron   Cl_{2}+2e^{-}\rightarrow 2Cl^{-}

Now add both balanced oxidation half and reduction half,  we get 

Cl_{2}+SO_{2}+2H_{2}O\rightarrow 2Cl^{-}+SO_{4}^{2-}+4H^{+}

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