1. 1
   A jewellery workshop electroplates a cheap metal ring with a thin layer of silver by passing an electric current through a solution containing silver ions, using the ring as one of the electrodes.

   (a)

   Which term describes the ring during this process?

   [1 mark]

   • AThe cathode, because it is the negative electrode where silver ions are reduced
   • BThe anode, because it is the positive electrode where silver ions are reduced
   • CThe cathode, because it is the positive electrode where silver ions are oxidised
   • DThe anion, because it attracts negative silver ions

   (b)

   Which statement correctly explains why the solution used for electroplating must contain freely moving ions?

   [1 mark]

   • AThe ions must be free to move so that the solution can change colour during electrolysis
   • BThe ions must be free to move to the electrodes to carry the current and be discharged there
   • CThe ions must be free to move so that covalent bonds can form between the electrodes
   • DThe ions must be free to move only to keep the solution electrically neutral overall

   (c)

   Explain why a solid ionic compound cannot be electrolysed, but the same compound can be electrolysed once it is molten or dissolved in water.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student in a school laboratory melts solid lead(II) bromide and electrolyses it using inert electrodes. A grey liquid forms at one electrode and an orange-brown gas is given off at the other.

   (a)

   What is the grey liquid formed at the cathode?

   [1 mark]

   • ASolid lead(II) bromide reforming
   • BMolten bromine
   • CMolten lead
   • DHydrogen gas condensing

   (b)

   Which half-equation correctly represents the reaction occurring at the anode during the electrolysis of molten lead(II) bromide?

   [1 mark]

   • APb2+ → Pb + 2e⁻
   • BPb2+ + 2e⁻ → Pb
   • C2Br⁻ + 2e⁻ → Br2
   • D2Br⁻ → Br2 + 2e⁻

   (c)

   Write the half-equation for the reaction at the cathode during the electrolysis of molten lead(II) bromide, and state whether this reaction is oxidation or reduction.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A technician electrolyses dilute sulfuric acid using inert electrodes in a school laboratory and collects a separate gas at each electrode, testing each gas to identify it.

   (a)

   Explain why hydrogen gas, rather than a metal, is produced at the cathode in this experiment.

   [3 marks]

   (b)

   The technician tests the gas collected at the anode with a glowing splint and it relights. Identify this gas, write the half-equation for its formation at the anode, and explain in terms of electron transfer why this reaction is classed as oxidation.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A chemical plant electrolyses concentrated aqueous sodium chloride solution (brine) using inert electrodes on an industrial scale, in order to manufacture several useful chemical products at once.

   (a)

   Describe what happens at each electrode during this process, including the products formed, and explain why these particular products are formed rather than sodium metal or oxygen.

   [6 marks]

   (b)

   The plant manager explains that if pure molten sodium chloride were electrolysed instead of the aqueous solution, sodium metal and chlorine gas would be formed directly at the electrodes. Explain, in terms of the ions present and the reactions at each electrode, why molten sodium chloride gives different products from aqueous sodium chloride solution.

   [6 marks]

   Total for question 4: 12 marks

End of questions