1. 1
   A metals company operates a large electrolysis plant to produce aluminium from aluminium oxide, mixed with another compound to lower its melting point.

   (a)

   What is aluminium oxide dissolved/mixed with in this industrial process?

   [1 mark]

   • ACryolite
   • BSodium chloride
   • CCalcium carbonate
   • DSulfuric acid

   (b)

   Why is aluminium extracted by electrolysis rather than by reduction with carbon, as is used for iron?

   [1 mark]

   • ABecause aluminium is less reactive than carbon
   • BBecause aluminium is more reactive than carbon, so carbon cannot reduce aluminium oxide
   • CBecause aluminium oxide does not contain any oxygen
   • DBecause aluminium is a gas at room temperature

   (c)

   Explain why the electrolysis process used to extract aluminium is expensive, referring to the energy requirements involved.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   During the electrolysis of molten aluminium oxide (mixed with cryolite), aluminium is collected at one electrode and oxygen gas is produced at the other, where it reacts with the carbon electrode itself.

   (a)

   At which electrode does aluminium form?

   [1 mark]

   • AThe positive electrode (anode)
   • BNeither electrode; it collects at the bottom of the cell without involving electrode reactions
   • CThe negative electrode (cathode)
   • DBoth electrodes equally

   (b)

   The carbon anode in this process must be replaced regularly during operation. Why is this necessary?

   [1 mark]

   • ABecause the carbon anode dissolves in the aluminium formed
   • BBecause the carbon anode becomes magnetic over time
   • CBecause the carbon anode melts due to the high temperature
   • DBecause the oxygen produced at the anode reacts with the carbon electrode, producing carbon dioxide and gradually wearing the electrode away

   (c)

   Write half-equations for the reactions occurring at the cathode and anode during the electrolysis of molten aluminium oxide.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   An engineering firm is designing a new aluminium extraction plant.

   (a)

   Explain why aluminium oxide must be mixed with cryolite and melted before electrolysis can take place, and describe what would happen if only solid aluminium oxide were used.

   [3 marks]

   (b)

   Describe the products formed at each electrode in this process, and explain why the carbon anodes need to be replaced periodically.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A country with abundant supplies of bauxite (aluminium ore) but limited access to cheap electricity is considering whether to build an aluminium extraction plant domestically or to export the ore for processing elsewhere.

   (a)

   Explain, in full, the chemistry and economics of extracting aluminium by electrolysis, and why this process is described as expensive.

   [6 marks]

   (b)

   Evaluate the environmental impact of aluminium extraction by electrolysis, and discuss why recycling aluminium is often promoted as a way to reduce this impact.

   [6 marks]

   Total for question 4: 12 marks

End of questions