Reaction of Chlorine
- A disproportionation reaction is a reaction in which the same species is both oxidised and reduced
- The reaction of chlorine with dilute alkali is an example of a disproportionation reaction
- In these reactions, the chlorine gets oxidised and reduced at the same time
- Different reactions take place at different temperatures of the dilute alkali
Chlorine in cold alkali (15 oC)
- The reaction that takes place is:
- The ionic equation is:
- The ionic equation shows that the chlorine gets both oxidised and reduced
- Chlorine gets oxidised as there is an increase in ox. no. from 0 to +1 in ClO–(aq)
- The half-equation for the oxidation reaction is:
- Chlorine gets reduced as there is a decrease in ox. no. from 0 to -1 in Cl–(aq)
- The half-equation for the reduction reaction is:
Chlorine in hot alkali (70 oC)
- The reaction that takes place is:
- The ionic equation is:
- The ionic equation shows that the chlorine gets both oxidised and reduced
- Chlorine gets oxidised as there is an increase in ox. no. from 0 to +5 in ClO3–(aq)
- The half-equation for the oxidation reaction is:
- Chlorine gets reduced as there is a decrease in ox. no. from 0 to -1 in Cl–(aq)
- The half-equation for the reduction reaction is:
Chlorine in Water Purification
- Chlorine can be used to clean water and make it drinkable
- The reaction of chlorine in water is a disproportionation reaction in which the chlorine gets both oxidised and reduced
The disproportionation reaction of chlorine with water in which chlorine gets reduced to HCl and oxidised to HClO
- Chloric(I) acid (HClO) sterilises water by killing bacteria
- Chloric acid can further dissociate in water to form ClO–(aq):
HClO(aq) → H+(aq) + ClO–(aq)
- ClO–(aq) also acts as a sterilising agent cleaning the water
Exam Tip
Adding chlorine to a water supply is an effective way to make the water safe to drink as it forms the sterilising agent HClO which in turn dissociates in water into another sterilising agent, ClO–(aq)