Required Practical: Electrolysis of Aqueous Solutions

🧪 Required Practical: Electrolysis of Aqueous Solutions

This is a required/core practical on every major GCSE chemistry specification (AQA, OCR, Edexcel) — not just AQA's. Examiners ask you to describe the method, identify variables, and explain safety precautions — often for 4-6 marks.

Method

1. Set up electrolysis apparatus with inert (carbon/graphite) electrodes in a beaker
2. Pour the aqueous solution (e.g., copper sulfate, sodium chloride) into the beaker, ensuring both electrodes are submerged
3. Connect the electrodes to a DC power supply using connecting wires and crocodile clips
4. Switch on the power supply and observe what forms at each electrode for several minutes
5. Test any gases produced: squeaky pop with a lighted splint for H₂; a glowing splint relights for O₂; damp litmus paper bleaches white for Cl₂
6. Record observations and repeat with different aqueous solutions

Key Variables

• Independent variable: Type of aqueous solution used (e.g., NaCl, CuSO₄, NaOH)
• Dependent variable: Products formed at each electrode (identity and amount)
• Control variables: Volume of solution, applied voltage, electrode material (inert carbon), time of electrolysis

Why Inert Electrodes?

Carbon/graphite electrodes are used because they do not react with the products or the electrolyte. If reactive metal electrodes were used (e.g., copper), the electrode itself would dissolve or react, changing the experiment — this is the principle behind electroplating (a different application).

Safety

• Chlorine gas is toxic — if electrolyzing chloride solutions, work in a well-ventilated area or under a fume cupboard. Do not inhale the gas
• Do not touch the electrodes when the power supply is switched on
• Wear eye protection throughout
• Copper sulfate solution is an irritant — avoid skin contact and wash hands after