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.
The given redox reaction can be represented as:
Cl2(s)+SO2(aq)+H2O(l)⟶Cl−(aq)+SO2−4(aq)
The oxidation half reaction is:
+4SO22(aq)⟶+6SO2−4(aq)
The oxidation number is balanced by adding two electrons as:
SO2(aq)⟶SO2−4(aq)+2e−
The charge is balanced by adding 4H+ ions as:
SO2(aq)+2H2O2−4(aq)+4H+(aq)+2e−
The O atoms and H+ ions are balanced by adding 2H2O molecules as:
SO2(aq)+2H2O(l)⟶SO2−4(aq)+2e− ⋯(i)
The reduction half reaction is:
0Cl2(s)⟶−1Cl−(aq)
The oxidation number is balanced by adding electrons
Cl2(s)+2e−⟶2Cl−(aq) ⋯(ii)
The balanced chemical equation can be obtained by adding equation (i) and (ii) as:
Cl2(s)+SO2(aq)+2H2O(l)⟶2Cl−(aq)+SO2−4(aq)+4H+(aq)