CIE A Level Chemistry复习笔记2.3.4 The 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 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 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