Question

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

(a) What is the substance of which the electrodes A and B are made?
(b) At which electrode (A or B) is the aluminium formed?
(c) What are the two aluminium compounds in the electrolyte C?
(d) Why is it necessary for electrode B to be continuously replaced?

Answer 1

(a) The electrodes A and B are made of carbon.
(b) Aluminium is formed at A (cathode; negative terminal).
(c) The two aluminium compounds present in electrolyte C is molten alumina (Al₂O₃) and cryolite (Na₃AlF₆).
(d) During the extraction of aluminium by electrolysis, oxygen gas is liberated at anode (B). Oxygen reacts with carbon anode and forms CO and ${\mathrm{CO}}_2$. Due to this oxidation reaction at anode, anode (B) needs to be continuously replaced.