(i)     Describe the production of aluminium from its purified ore. Explain the role of cryolite and deduce the equations for the reactions occurring at the two electrodes.

Production of aluminium:

Role of cryolite:

Negative electrode (cathode):

Positive electrode (anode):

(ii)     Outline why aluminium was not available in large quantities before 1900.

(i)     State one advantage of using an alloy rather than the pure metal.

(ii)     Outline why the range of metals alloyed with aluminium for this use is very limited.

Suggest one possible environmental impact that can result from the large-scale production of aluminium.

(i)     Production of aluminium:

electrolysis of molten alumina/aluminium oxide/\({\text{A}}{{\text{l}}_{\text{2}}}{{\text{O}}_{\text{3}}}\);

Role of cryolite:

(molten) cryolite (saves money due to) lower operating temperature / solvent with a lower melting point (than aluminium oxide);

Accept lowers the melting point of aluminium oxide.

Negative electrode (cathode):

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

Positive electrode (anode):

\({\text{2}}{{\text{O}}^{2 - }}{\text{(l)}} \to {{\text{O}}_2}{\text{(g)}} + {\text{4}}{{\text{e}}^ - }\);

Allow e for e^–.

Ignore state symbols.

Penalize use of equilibrium sign once only.

Award [1 max] for M3 and M4 if correct equations are given but at the wrong electrodes.

(ii)     no electricity / electricity not widely available before 1900;

(i)     to control/improve properties / alloys are stronger/more durable/less reactive/less malleable/less ductile than pure metals;

(ii)     only a small number of metals have low densities / many low density metals are too reactive / alloys need presence of other metallic atoms of slightly different size (few metals like this);

(purification of ore produces) waste \({\text{F}}{{\text{e}}_2}{{\text{O}}_3}\)/iron(III) oxide/red mud;

carbon dioxide/ \({\text{C}}{{\text{O}}_2}\) from burning electrodes;

environmental impacts of power generation;

aluminium production a significant contributor to global warming;

mining the ore damages the landscape/local ecology;

generation of fluorides/polyfluorinated carbons/fluorine containing waste products;

(i)     Many candidates understood the principles behind the production of aluminium and the role of the cryolite, although not always managing to state the principles accurately to be able to score the first two marks, but many candidates showed weakness in writing the correct half-equations at the correct electrodes. 

(ii)     About half of the candidates stated the there was no electricity available at that time.

(i)     More than half of the candidates were able to give an advantage of using an alloy over using the pure metal. A few candidates stated the misconception that alloys were less brittle than pure metals.

(ii)     Some candidates offered sensible suggestions mainly focusing on the importance of finding a low density metal.

Quite well answered. Not many candidates discussed the impact of the purification of the bauxite or its mining. Candidates focused on the impact of the generation of large amounts of electricity and global warming.