1. 1
   A student electrolyses molten lead bromide (PbBr2) using inert graphite electrodes connected to a direct current supply. Bubbles of brown gas form at one electrode and a silvery liquid metal collects at the other.

   (a)

   Which statement correctly describes the ions present in molten lead bromide?

   [1 mark]

   • APb2+ cations and Br- anions, both free to move
   • BPb2+ cations only, with Br atoms fixed in place
   • CPbBr2 molecules with no charged particles
   • DBr- anions only, with Pb atoms fixed in place

   (b)

   At which electrode does the silvery liquid lead form, and why?

   [1 mark]

   • AThe anode, because bromine is denser than lead
   • BThe anode, because positively charged Pb2+ ions migrate to the positive electrode
   • CThe cathode, because negatively charged Pb2+ ions migrate to the negative electrode
   • DThe cathode, because positively charged Pb2+ ions migrate to the negative electrode

   (c)

   Explain, in terms of electron transfer, what happens to the bromide ions at the anode during this electrolysis.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A technician sets up two separate electrolysis cells, each with inert graphite electrodes connected to a direct current supply. Cell 1 contains concentrated sodium chloride solution. Cell 2 contains dilute sulfuric acid.

   (a)

   In Cell 1, a pale green gas with a distinctive smell is collected at the anode. Which gas is this?

   [1 mark]

   • AHydrogen
   • BOxygen
   • CChlorine
   • DCarbon dioxide

   (b)

   In Cell 2 (dilute sulfuric acid), which gas forms at the cathode and in what ratio of volumes compared with the gas at the anode?

   [1 mark]

   • AOxygen forms at the cathode, in a 1:2 ratio with hydrogen at the anode
   • BHydrogen forms at the cathode, in a 2:1 ratio with oxygen at the anode
   • CHydrogen forms at the cathode, in a 1:1 ratio with oxygen at the anode
   • DSulfur dioxide forms at the cathode, in a 2:1 ratio with oxygen at the anode

   (c)

   Explain why hydrogen, rather than sodium, is produced at the cathode in Cell 1 (sodium chloride solution).

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A jewellery company wants to purify impure copper recovered from recycled electrical wire so it can be reused. They set up an electrolysis cell containing copper sulfate solution, with a rod of impure copper as the anode and a strip of pure copper as the cathode.

   (a)

   Write the half equation for the reaction occurring at the cathode, and explain what happens to its mass during electrolysis.

   [3 marks]

   (b)

   Explain what happens to the impure copper anode during this process, and describe what happens to any impurities that were present in it, such as silver and gold.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A GCSE class carries out the core practical investigation into the electrolysis of copper sulfate solution, first using two inert graphite electrodes, then repeating with two copper electrodes. They record their observations at both electrodes in each version of the experiment.

   (a)

   Describe, in full detail, what would be observed at the anode and cathode when copper sulfate solution is electrolysed using inert graphite electrodes. In your answer, refer to the ions present in the solution, which ions are discharged at each electrode, and the equations for the reactions taking place.

   [6 marks]

   (b)

   The class then repeats the experiment using two copper electrodes instead of inert graphite electrodes. Explain how the observations at the anode and cathode differ from the inert-electrode version, why this happens, and why this version of the experiment is used industrially to purify copper.

   [6 marks]

   Total for question 4: 12 marks

End of questions