AQA A Level Chemistry

Revision Notes

2.3.4 Uses & Reactions of Chlorine

Reactions of Halide Ions

  • 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:

Group 17 - General Equation, downloadable AS & A Level Chemistry revision notes

  • The ionic equation is:

Group 17 - Ionic Equation, downloadable AS & A Level Chemistry revision notes

  • 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:

Group 17 - Oxidation Half-Equation, downloadable AS & A Level Chemistry revision notes

  • 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:

Group 17 - Reduction Half-Equation, downloadable AS & A Level Chemistry revision notes

Chlorine in hot alkali (70 oC)

  • The reaction that takes place is:

Group 17 - General Equation 2, downloadable AS & A Level Chemistry revision notes

  • The ionic equation is:

Group 17 - Ionic Equation 2_1, downloadable AS & A Level Chemistry revision notes

  • 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:

Group 17 - Oxidation Half-Equation 2, downloadable AS & A Level Chemistry revision notes

  • 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:

Group 17 - Reduction Half-Equation 2, downloadable AS & A Level Chemistry revision notes

Chlorine

  • 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

 

Group 17 - Chlorine and Water Reaction, downloadable AS & A Level Chemistry revision notes

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)

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