2.3.4 Uses & Reactions 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 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
• This reaction is important in the purification of water for drinking and swimming pools

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
• Chlorine is used in water treatment to kill bacteria
  • It has been used to treat drinking water and the water in swimming pools
• The benefits to health of water treatment by chlorine by its killing of bacteria outweigh its risks of toxic effects and possible risks from the formation of chlorinated hydrocarbons
• In shallow swimming pools chlorine is rapidly lost from the water, so the chlorine has to be topped up on a regular basis adding to cost
  • This is because it is more exposed to sunlight
• In sunlight, the following reaction occurs:

2Cl₂ (g) + 2H₂O (l) → 4HCl (aq) + O₂ (g)