Electrolysis of Water
What is the electrolysis of water?
- Electrolysis of water is the process of using electricity to split water into hydrogen and oxygen
2H2O (l) → 2H2 (g) + O2 (g)
- This process can be done using a Hoffman voltameter
- When the current flows:
- Hydrogen ions, H+, in the water are attracted to the cathode
- They gain electrons (reduced) and hydrogen gas is formed
2H+ (aq) + 2e– (aq) → H2 (g)
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- Hydroxide ions, OH–, in the water are attracted to the anode
- They lose electrons (oxidised) and oxygen gas is formed
2OH– (aq) → O2 (g) + 2H+ (aq) + 4e–
The Hoffman voltameter
The Hoffman voltameter is used to split water into two gases, hydrogen and oxygen
- In the overall equation you will notice that there are 2 moles of hydrogen gas produced compared to 1 mole of oxygen
- This is shown in the experiment as the volume of hydrogen gas formed is double the volume of oxygen gas
- The gases formed at each electrode can be tested for
Examiner Tip
You should be able to write the a balanced equation to show the reaction taking place at the cathode, but you are not expected to recall the equation taking place at the anode.
Cathode:
2H+ (aq) + 2e– (aq) → H2 (g)
Anode:
2OH– (aq) → O2 (g) + 2H+ (aq) + 4e–
Higher tier candidates should be able to balance the equation for the reaction at the anode.
