Electrolysis of aqueous solutions — required practical

AQA GCSE Chemistry

Investigate what is produced at the electrodes when aqueous solutions are electrolysed.

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Method

  1. Set up a beaker with the solution, two inert (carbon) electrodes and a power supply.
  2. Switch on and observe/test the products at each electrode.
  3. Test gases: a lit splint (pop = hydrogen), a glowing splint (relights = oxygen), damp litmus (bleached = chlorine).

Variables

  • Independent variable: The solution electrolysed
  • Dependent variable: The products at the cathode and anode
  • Control variables: Voltage, time, type of electrode, concentration

Results & analysis

At the cathode you get the less reactive of hydrogen and the metal (usually hydrogen unless the metal is less reactive than hydrogen, e.g. copper). At the anode you get oxygen, unless the solution contains a halide (then the halogen, e.g. chlorine).

Risk assessment

  • Chlorine is toxic — use a well-ventilated room; wear eye protection.

Improving accuracy & reliability

  • Use clean, inert electrodes; test gases promptly.
Exam tip: Cathode = reduction (H⁺ or metal ions gain electrons); anode = oxidation. Remember the halide-vs-oxygen rule at the anode.

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