Question

During electrolysis of an aqueous solution of sulphuric acid between platinum electrodes, two types of anions migrate towards the anode but only one of them is discharged:

1. Name the two anions.
2. Name the main product of the discharge of anion at the anode and write the anode reaction.
3. Name the product at the cathode and write the reaction.
4. Do you notice any change in colour. State why?
5. Why this electrolysis, is considered as an example of catalysis?

Answer 1

1. Two anions are \[\ce{SO^2-_4 {and} OH-}\].
2. Main product is oxygen gas.
   \[\ce{OH- - e- -> OH}\]
   \[\ce{4OH -> 2H2O + O2_{(g)}}\]
3. Main product is \[\ce{[H3O+].[H^1+ - e- ->H]}\]
   \[\ce{[H + H -> H2]}\]
4. No, there is no change in colour, the electrodes are inert.
5. Water is a poor conductor of electricity. It does not form ions.

When diluted sulphuric acid is added. Water's polarity causes it to ionise and form an electrolyte. This is recognised as an example of catalysis.