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NCERT Class XI Chemistry Redox Reactions Solutions

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Question : 23 of 30
Marks: +1, -0
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.
Solution:  
The skeletal equation is : Cl2(g)+SO2(g)+H2O(l)\mathrm{Cl}_{2(g)} + \mathrm{SO}_{2(g)} + \mathrm{H_2O}_{(l)} → Cl(aq)−+SO42−(aq)\mathrm{Cl}^{-}_{(aq)} + \mathrm{SO_4^{2-}}_{(aq)}
Reduction half equation : Cl(2g)+2e−\mathrm{Cl}_{(2g)} + 2e^{-} → 2Cl(aq)−2\mathrm{Cl}^{-}_{(aq)} ... (i)
Oxidation half equation : SO2(g)+2H2O(l)\mathrm{SO}_{2(g)} + 2\mathrm{H_2O}_{(l)} → SO42−(aq)+4H+(aq)+2e−{\mathrm{SO}_4^{2-}}_{(aq)} + 4{\mathrm{H}^{+}}_{(aq)} + 2e^{-} ... (ii)
Adding Eq. (i) and Eq. (ii), we get,
Cl2(g)+SO2(g)+2H2O(l)\mathrm{Cl}_{2(g)} + \mathrm{SO}_{2(g)} + 2\mathrm{H_2O}_{(l)} →2Cl−(aq)+SO42−(aq)+4H+(aq)2{\mathrm{Cl}^{-}}_{(aq)} + {\mathrm{SO}_4^{2-}}_{(aq)} + 4{\mathrm{H}^{+}}_{(aq)}
This represents the balanced redox reaction.
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