Electrolysis: GCSE Chemistry Definition

What is electrolysis?

In GCSE Chemistry, electrolysis is the breakdown of an ionic compound (electrolyte) using electricity. For any given electrolyte, you can predict the products formed at the two electrodes.

The ionic compound needs to be molten or in solution so that it can conduct electricity. Molten ionic compounds will produce the corresponding metal at the cathode (negative electrode) and non-metal at the anode (positive electrode). For example, during the electrolysis of molten lead bromide, lead is formed at the cathode, and bromine at the anode. 

Aqueous solutions contain the ions in the ionic compound, as well as H⁺ and OH^- from water. During the electrolysis of a solution, the product formed at the cathode depends on the reactivity of the elements that make up the positive ions. The element of the less reactive ion will form at the cathode. If halide ions are present in the solution, the halogen will form at the anode.

For example, the electrolysis of aqueous sodium chloride produces hydrogen at the cathode (because hydrogen is less reactive than sodium) and chlorine at the anode (chloride ions are halide ions).

If halide ions aren’t present, oxygen will form at the anode. For example, the electrolysis of aqueous copper(II) sulfate produces copper at the cathode (because copper is less reactive than hydrogen) and oxygen at the anode. 

Electrolysis Revision Resources to Ace Your Exams

Most exam boards will expect you to be able to identify the products formed during the electrolysis of a range of electrolytes. Make sure you use our topic questions to apply knowledge to exam style questions and consolidate your learning using flashcards.

Explore Our GCSE Chemistry Revision Resources