1. 1
   A technician melts a sample of lead bromide and passes an electric current through it using two inert electrodes. Bubbles of orange-brown gas form at one electrode, and a grey liquid metal collects at the other.

   (a)

   Why is the lead bromide able to conduct electricity and be broken down in this molten state?

   [1 mark]

   • ABecause the ions are fixed in place and cannot move
   • BBecause the ions are free to move and carry electrical charge
   • CBecause lead bromide is a gas at this temperature
   • DBecause the electrodes react with each other directly

   (b)

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

   [1 mark]

   • AAt the cathode, because positive lead ions move there and gain electrons
   • BAt the anode, because positive lead ions move there and gain electrons
   • CAt the cathode, because negative lead ions move there and lose electrons
   • DAt the anode, because negative bromide ions move there and lose electrons

   (c)

   Write half-equations for the reactions occurring at each electrode during the electrolysis of molten lead bromide, and state which electrode process is oxidation and which is reduction.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student dissolves solid potassium iodide in water to make a solution, then attempts to pass an electric current through the solid potassium iodide crystals before dissolving them. No current flows through the solid crystals.

   (a)

   Why does the solid not conduct electricity, even though it will conduct once dissolved?

   [1 mark]

   • AThe solid is actually a good conductor, but the equipment was faulty
   • BSolid potassium iodide contains no ions at all
   • CSolid potassium iodide is a covalent compound
   • DIn the solid, the ions are held in fixed positions in a lattice and cannot move to carry charge

   (b)

   Once the potassium iodide is dissolved in water and electrolysed using inert electrodes, which ions move towards the cathode (negative electrode)?

   [1 mark]

   • AIodide ions (I-)
   • BHydroxide ions (OH-)
   • CPotassium ions (K+)
   • DElectrons directly, with no ion movement

   (c)

   Define the terms 'electrolyte', 'oxidation' and 'reduction' as they apply to this electrolysis experiment.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   An engineer is designing an industrial electrolysis cell to break down molten zinc chloride into its elements, using inert electrodes connected to a direct current power supply.

   (a)

   Describe the movement of ions within the molten zinc chloride during electrolysis, and explain why the substance must be molten (or dissolved) rather than solid for this process to work.

   [3 marks]

   (b)

   Write balanced half-equations for the reactions occurring at the cathode and the anode during the electrolysis of molten zinc chloride, and explain each reaction in terms of oxidation and reduction.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A company wants to extract pure zinc metal and chlorine gas from zinc chloride using electrolysis on an industrial scale.

   (a)

   Explain, in full detail, how electrolysis of molten zinc chloride works, including the roles of the electrodes, the movement of ions, and the definitions of oxidation and reduction as applied to this process.

   [6 marks]

   (b)

   Evaluate the practical and safety considerations the company must address when running this electrolysis process on an industrial scale, given that chlorine gas is toxic and molten zinc chloride is at a high temperature.

   [6 marks]

   Total for question 4: 12 marks

End of questions