Electrolysis of Copper Sulfate Solution

• What colour is CuSO4(aq)?

  Blue
• What is an electrolyte?

  An ionic compound which is molten or dissolved in water
• What is electrolysis?

  The splitting up of the electrolytes using electrical energy
• Half equation for the reaction occurring at the cathode when CuSO4 is electrolysed?


  Cu 2+ (aq) + 2e - => Cu (s)
• Write a half equation for the formation of oxygen from OH- ions 


  4OH - (aq) => 2H2O (l) + O2 (g) + 4e -
• At which electrode does oxidation occur?


  Positive electrode (anode)
• What forms at the cathode and the anode in electrolysis?

  Cathode - metals or hydrogen

  Anode - non-metals
• What are the products of electrolysis of copper sulphate when using inert electrodes?

  Copper at negative electrode, oxygen at positive electrode
• How do you set up an electrochemical cell?

  Place positive and negative electrodes in a beaker containing a molten or dissolved ionic compound. Connect both electrodes to a power supply with wires.
• When carrying out the electrolysis of CuSO4, what safety precautions should be taken?

  Wear gloves and safety goggles (copper sulfate causes skin and eye irritation), keep propanone (for drying the electrodes) away from flames and use in fume cupboard.
• What observations could you make when CuSO4 is electrolysed using inert electrodes?

  Cathode - copper deposit (brown/pink solid), anode - bubbles of O2 gas, solution - blue colour fades
• You are using copper electrodes for the electrolysis of CuSO4, over time what happens to the anode?

  Mass will decrease. Cu(s) in the electrode oxidised to Cu2+(aq)
• You are using copper electrodes for the electrolysis of CuSO4, how are the change in masses of the electrodes linked?

  The mass lost from the anode should be the same as the mass gained by the cathode.
• When copper electrodes are used for the electrolysis of CuSO4, what is the relationship between the mass gained by the cathode and the current used?

  The mass gained by the cathode is directly proportional to the current used (for a given time)
• Why must you clean the copper electrodes with emery paper before use?

  To remove any copper oxide which may have formed
• Why should you dry the copper electrodes at the end of the electrolysis of CuSO4?

  So the change in mass is only caused by the gain/loss of copper atoms.