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ASChemistryAQARevision Notes2. Inorganic Chemistry2.3 Group 7 (17), the Halogens2.3.4 Uses & Reactions of Chlorine

Uses & Reactions of Chlorine (AQA AS Chemistry)

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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

  • 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

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
  • 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)

Examiner 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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    Stewart

    Author: Stewart

    Expertise: Chemistry Lead

    Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Exam Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.