A manufacturer extracts aluminium from purified aluminium oxide. Fig. 1 shows an electrolysis cell used at a temperature high enough for the electrolyte to ...
Question 1 Report
A manufacturer extracts aluminium from purified aluminium oxide. Fig. 1 shows an electrolysis cell used at a temperature high enough for the electrolyte to be molten. Cryolite is mixed with the aluminium oxide to lower the operating temperature. The carbon anodes are connected to the positive terminal of the power supply. Liquid aluminium forms at the bottom of the cell.
(a) Name the electrode labelled X and the product labelled Y. [2]
(b) State why the aluminium oxide must be molten. [1]
(c) Complete the half-equation at the negative electrode.
Al3+ + ............ → Al [2]
(d) Explain why the carbon anodes have to be replaced regularly. [3]
Answer Details
(a) X is the carbon anode/positive electrode; Y is aluminium. [2]
(b) Aluminium oxide must be molten so its ions can move through the liquid and conduct electricity. [1]
(c) Aluminium ions gain three electrons at the negative electrode:
\[\mathrm{Al^{3+}+3e^-\rightarrow Al}\]\(\mathrm{3e^-}\) [1], on the left-hand side [1].
(d) Oxide ions form oxygen at the anode. The oxygen reacts with carbon, making carbon dioxide, so the carbon anodes are gradually used up and must be replaced. [3]
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