1. 1
   As part of a required practical, a student sets up a circuit with two inert carbon electrodes dipped into copper sulfate solution, connected to a power supply. After switching on the current, the student notices a pink-brown coating building up on one electrode, while bubbles of gas form at the other.

   (a)

   Which electrode does the pink-brown coating form on?

   [1 mark]

   • AThe anode, because copper ions are attracted there
   • BThe cathode, because copper ions are attracted there and gain electrons
   • CThe anode, because sulfate ions are reduced there
   • DThe cathode, because water molecules are oxidised there

   (b)

   What gas is most likely to be produced at the electrode where bubbles form, using inert electrodes in copper sulfate solution?

   [1 mark]

   • AHydrogen
   • BChlorine
   • COxygen
   • DCarbon dioxide

   (c)

   Write the half-equation for the reaction occurring at the electrode where the pink-brown coating forms, and explain why this reaction is described as reduction.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A group of students repeats the copper sulfate electrolysis required practical, this time carefully collecting and testing the gas produced at the anode with a glowing splint. The splint relights.

   (a)

   What does this confirm about the gas?

   [1 mark]

   • AThe gas is oxygen
   • BThe gas is carbon dioxide
   • CThe gas is hydrogen
   • DThe gas is chlorine

   (b)

   Where in the electrolysis cell would the students have collected this gas from, in order to test it with a glowing splint?

   [1 mark]

   • AAt the cathode, where copper is deposited
   • BFrom the power supply itself
   • CDissolved in the copper sulfate solution only
   • DAt the anode, where oxidation occurs

   (c)

   Write the half-equation for the formation of the gas at the anode, and explain why this reaction is described as oxidation.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student carries out the required practical investigating the products at the anode and cathode in the electrolysis of copper sulfate solution.

   (a)

   Describe how the student would set up the apparatus using inert electrodes, and describe the observation expected at the cathode.

   [3 marks]

   (b)

   Describe the observation and appropriate confirmatory test the student would carry out at the anode, and explain, using ion movement, why the products differ between the two electrodes.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A technician carries out the required practical to investigate the products formed at the anode and cathode during electrolysis of copper sulfate solution using inert electrodes.

   (a)

   Describe, in full, the method used, the expected products at each electrode, and the tests used to confirm their identities.

   [6 marks]

   (b)

   Evaluate possible sources of error in this required practical and suggest improvements to ensure the products at each electrode are correctly identified.

   [6 marks]

   Total for question 4: 12 marks

End of questions