Electrolysis

Investigate what happens when aqueous solutions are electrolysed using inert electrodes.

In this required practical, students are required to pass an electric current through two different salt solutions. They must identify the elements formed at each of the two electrodes. Students must also draw a fully labelled diagram of their electrochemical cells.

Equipment (per participant)

• Safety goggles
• 100ml beaker
• Petri dish
• 4 x carbon electrodes
• 4mm lead (black)
• 4mm lead (red)

• 2 x crocodile clips
• Bench power supply
• Blue litmus paper
• Forceps
• Copper (ii) Chloride (0.5M)
• Sodium Chloride (0.5M)

Method

Students should collect the necessary equipment. They fill their 100ml beaker to the 50ml mark with Copper (ii) Chloride solution.
The petri dish lid, which needs to be provided to the students with two holes wide enough for the electrodes, is placed over the 100ml beaker containing the Copper (ii) Chloride solution. A carbon electrode is inserted through each of the holes. The students must take care to make sure that the rods do not touch each other.
Crocodile clips are then attached to the top of the electrodes and the connecting leads are connected to the DC terminals on the bench power supply (red and black).
Students should ensure the power supply is set at 4 Volts and switch it on.
Both electrodes are observed during the reaction to see what happens. Students must record their observations in a suitable table.
Using a pair of forceps, students should hold a piece of blue litmus paper in the solution next to the positive electrode (anode). Their observations should be recorded in their table. Are students able to identify the element being formed?
The students should switch off the power supply and clean the apparatus. Using a new pair of carbon electrodes, students should set up the equipment as they did before but using the Sodium Chloride solution to fill the beaker instead.
They should record their observations in their table.

Technician tips

• To make a 0.5M solution of Sodium Chloride, 29.22g of salt is dissolved in 1 litre of water.
• To make a 0.5M solution of Copper (ii) Chloride, 85.24g of the powder is dissolved in 1 litre of water
• A home-made electrolysis cell also works well for this required practical. Holes could be made in petri dish lids by heating an item of similar diameter to your electrodes (e.g. the end of a glass or metal rod) and pushing the item through the petri dish lid. The carbon electrodes could be secured further using rubber bungs. The use of bungs would lower the risk of students short circuiting the equipment by allowing the carbon electrodes to touch.