Explain the function of the molten cryolite.

State the half-equations for the reactions that take place at each electrode.

Positive electrode (anode):

Negative electrode (cathode):

Outline two different ways that carbon dioxide may be produced during the production of aluminium.

melting point of the cryolite solution is much lower than the melting point of alumina/Al2O3 / it lowers the melting point of the mixture / cell operates at lower temperature;

Allow lowers melting point or lowers melting point of aluminium oxide.

Do not allow lowers melting point of aluminium.

Positive electrode:

\({\text{2}}{{\text{O}}^{2 - }} \to {{\text{O}}_2} + {\text{4}}{{\text{e}}^ - }/{{\text{O}}^{2 - }} \to \frac{1}{2}{{\text{O}}_2} + {\text{2}}{{\text{e}}^ - }\);

Negative electrode:

\({\text{A}}{{\text{l}}^{3 + }} + {\text{3}}{{\text{e}}^ - } \to {\text{Al}}\);

Award [1] for correct equations but wrong electrodes.

Allow e instead of \({e^ - }\).

use of fossil fuels (to provide energy);

oxidation of the (graphite) positive electrode/anode;

This was either answered very well or very poorly.

Only the best candidates could state half-equations for the electrolysis of aluminium.

Many candidates scored one mark out of two for outlining how carbon dioxide may be produced during aluminium production in (b). C.1.10 states that candidates should know the environmental impacts of aluminium production.