Required Practical: Electrolysis — AQA GCSE Chemistry

This required practical investigates the products formed when aqueous solutions are electrolysed using inert electrodes.

Apparatus

• A beaker or electrolysis cell containing the solution (electrolyte).
• Two inert electrodes (usually graphite/carbon).
• A d.c. power supply connected to the electrodes.

Method

1. Half-fill the cell with the solution (e.g. copper sulfate or sodium chloride solution).
2. Connect the electrodes to the power supply (one positive anode, one negative cathode).
3. Switch on and observe what forms at each electrode.
4. Test any gases produced (e.g. lighted/glowing splint, damp litmus paper).

Predicting and identifying products

Use the electrolysis rules:

• Cathode: hydrogen, unless the metal is less reactive than hydrogen (then the metal is deposited, e.g. copper).
• Anode: a halogen if a halide is present, otherwise oxygen.

For example:

• Copper sulfate → copper (cathode), oxygen (anode).
• Sodium chloride solution → hydrogen (cathode), chlorine (anode).

Safety

• Chlorine is toxic — use small quantities and good ventilation.
• Use low voltage d.c.

Exam tips

• Use inert electrodes and a d.c. supply.
• Apply the cathode/anode rules to predict products.
• Test gases (splint tests, damp litmus for chlorine).
• Copper deposits on the cathode because it is less reactive than hydrogen.