1. 1
   An aluminium smelting plant extracts aluminium by electrolysis of molten aluminium oxide dissolved in molten cryolite, using carbon electrodes.

   (a)

   At which electrode does the molten aluminium metal form?

   [1 mark]

   • AAluminium forms in the electrolyte, not at an electrode
   • BThe anode (positive electrode)
   • CBoth electrodes equally
   • DThe cathode (negative electrode)

   (b)

   Why is the aluminium oxide dissolved in molten cryolite rather than being melted on its own?

   [1 mark]

   • ACryolite makes the aluminium oxide conduct electricity for the first time
   • BCryolite prevents any electrolysis from taking place
   • CCryolite reacts with the aluminium oxide to directly produce aluminium metal
   • DCryolite lowers the melting point of the mixture, reducing the energy needed

   (c)

   The carbon positive electrodes (anodes) in the smelting plant need to be replaced regularly. Explain why this is necessary.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A jewellery workshop electroplates a silver ring with a thin layer of gold using electrolysis, with a gold electrode and a solution containing gold ions, to give the ring a more expensive appearance at lower cost.

   (a)

   At which electrode should the silver ring be placed so that gold is deposited onto it?

   [1 mark]

   • AThe ring should not be connected to the circuit at all
   • BThe anode (positive electrode)
   • CIt does not matter which electrode is used
   • DThe cathode (negative electrode)

   (b)

   What happens to the gold ions in solution as they reach the ring during electroplating?

   [1 mark]

   • AThey lose electrons and are oxidised to form gold metal
   • BThey remain as ions and do not change at all
   • CThey react with water to form gold oxide
   • DThey gain electrons and are reduced to form gold metal

   (c)

   Suggest two reasons why the workshop chooses to electroplate the silver ring with gold rather than making the whole ring from solid gold.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student in a school laboratory electrolyses an aqueous solution of copper sulfate using inert graphite electrodes, and records the changes observed at each electrode over time.

   (a)

   Predict the product formed at the cathode and the product formed at the anode, giving a reason for the product formed at the cathode.

   [3 marks]

   (b)

   Write half equations for the reactions occurring at the cathode and the anode, and state whether each is an oxidation or a reduction reaction.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Compare the electrolysis of molten lead bromide with the industrial electrolysis of concentrated aqueous sodium chloride solution (the chlor-alkali process), which produces chlorine gas, hydrogen gas and sodium hydroxide solution as useful industrial products.

   (a)

   Describe the products formed at each electrode in both processes and explain why they differ, referring to the physical state of each compound and the ions present.

   [6 marks]

   (b)

   Evaluate the importance of the chlor-alkali process to industry, considering the uses of its three products (chlorine, hydrogen and sodium hydroxide) and any economic or environmental considerations of running this process at a large scale.

   [6 marks]

   Total for question 4: 12 marks

End of questions