Products of Electrolysis of Sodium Chloride

Remember 9.1 Practical Skills Practical Skills

Method:

  1. Prepare one beaker of dilute sodium chloride solution and one beaker of concentrated sodium chloride solution.
  2. Set up two electrolytic cells using two beakers. A current should be run through the beakers on at a time.
  3. Place a test tube at both electrodes, taking care to trap any gas formed during the reaction.
  4. Place a pH meter at both the electrodes of the dilute sodium chloride solution.
  5. Light a splint, gently blow it out, and place near each of the two electrodes in the dilute sodium chloride solution beaker in quick succession.
  6. Repeat steps 3 to 5 for the beaker containing the concentrated sodium chloride solution.
  7. Waft (ideally, conduct the experiment in a fume cupboard) any gases formed during the experiment carefully towards yourself to identify its contents.
  8. Place a piece of litmus paper each at both electrodes of the concentrated sodium chloride solution.

Expected Results:

  • The pH was below 7 at the anode, and above 7 at the cathode. This indicates the self-ionisation of water brought about by the unresponsiveness of sodium ions to reduction where water is present.
  • A re-lighted splint indicates the presence of oxygen.
  • A popping sound produced when gas caught in a test tube is ignited indicates the presence of hydrogen gas.
  • Chloride gas has a distinct odour which is immediately identifiable.
  • The bleaching of litmus paper at the anode of the concentrated sodium chloride solution confirms the presence of chloride gas.