Question

The following is a sketch of an electrolytic cell used in the extraction of aluminium:

1. What is the substance of which the electrodes A and B are made?
2. At which electrode (A or B) is aluminium formed?
3. What are the two aluminium compounds in the electrolyte C?
4. Why is it necessary for electrode B to be continuously replaced?
   

Answer 1

1. Electrode A is made of carbon gas, and electrode B is made of carbon rods.
2. At electrode A.
3. Two compounds in the electrolyte C are Al₂O₃ and Na₃AlF₆.
4. As at electrode B, oxygen is liberated during the process. The oxygen liberated oxidises the carbon anode, producing CO and CO₂. Thus, electrode B is to be replaced continuously.

Answer 2

1. A is made of carbon and B is a thick graphite rod.
   A → Cathode
   B → Anode
2. Aluminium is generated at the cathode at A in a molten condition and can be extracted through a tapping hole.
3. The two aluminium compounds in the electrolyte C are Na₃AlF₆ and Al₂O₃.
4. At the anode, oxygen is released when it combines with carbon to create carbon monoxide. CO₂ is created as the heated CO burns further. Consequently, the anode wears out and needs to be replaced periodically.