Uses of Chlorine (OCR A Level Chemistry A): Revision Note

Reactions of Chlorine

• A disproportionation reaction is a reaction in which the same species is both oxidised and reduced

• The reaction of chlorine with water and cold, dilute aqueous alkali are examples of  disproportionation reactions

• In these reactions, the chlorine gets oxidised and reduced at the same time

The reaction of chlorine with water

• 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

• If some universal indicator is added to the solution it will first turn red due to the acidity of both reaction products. It will then turn colourless as the HClO bleaches the colour.

The reaction of chlorine with cold, dilute aqueous sodium hydroxide

• 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:

• The mixture of NaCl and NaClO (sodium chlorate (I)) is used as Bleach and to disinfect/ kill bacteria

Treating Water

• Adding chlorine to a water supply is an effective way to make the water safe to drink

  • The chlorine reacts to form the sterilising agent HClO

  • The HClO in turn dissociates in water into another sterilising agent, ClO^- (aq)

• 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