Theory behind this practical:

By completing this practical, you will be able to observe the products. When copper (II) sulphate solution is electrolysed, copper is produced at the cathode (because copper is less reactive than hydrogen) and oxygen is produced at the anode (because hydroxide ions are less stable than sulphate ions). You will be able to see a new layer of copper forming on the cathode.

A teacher may demonstrate the same with copper (II) chloride. Here chlorine will form at the anode as chlorine is less reactive than the sulphate. This is rarely done as a class practical due to the intensity of the chlorine smell.

Method:

  • Attach two clean strips of copper, one to each of the crocodile clips.
  • Lower the frame into the copper sulphate solution ensuring that the clips do not touch the solution and that the copper strips are not touching.
  • Attach cables from the crocodile clips to the power supply’s DC connections.
  • Ensure that the voltage does not exceed 6V then turn of the power supply and begin making observations.

You may also measure the dry mass of each electrode before and after a set time to calculate the production rate of copper.

Your teacher may allow you to try electroplating. To do this, swap the strip of copper on the cathode for a clean coin and run the experiment further. (Note, this may stop your coin from being recognised in a vending machine so use low value coins).

  • All copper (II) sulphate solution must be poured into the bucket at the end, it must not go down the sink

Technician notes:

  • Bottles of copper (II) sulphate solution
  • Beakers
  • Crocodile clips mounted on plastic tracks
  • Wires
  • Power packs limited to 6V
  • Balances (to find mass of copper strips) – optional
  • Bucket to collect copper(II) solution

Staff demonstration

  • As above but larger to allow for the collection of anode gases
  • Copper chloride solution as an alternative electrolyte (show chlorine production)
  • 2 boiling tubes (oxygen -relights glowing splint / chlorine – smell)

Safety:

Usual lab rules must be adhered to:

  • Lose hair tied up
  • Goggles on throughout the lesson – copper sulphate solution causes severe eye damage
  • Bags away and stools tucked under
  • Notify the teacher immediately if any spills or breakages occur
  • Copper sulphate solution must not go down the drain – causes serious and long term damage to aquatic life.

For further/more detailed information, check all reagents and practices at CLEAPSS.