4.4 Chemical changes - Electrolysis

Unit Summary

This unit aligns with the AQA GCSE Chemistry: Trilogy specification and is designed to be delivered flexibly while maintaining a coherent learning progression. It builds upon prior knowledge from earlier topics such as ionic bonding, structure and properties of materials, and the reactivity of metals. The aim is to develop a deep understanding of electrolysis as both a chemical and industrial process, exploring how electrical energy is used to bring about chemical change.

Students will study the principles of electrolysis, including the movement of ions in electrolytes, the reactions at electrodes, and how these are represented using half-equations. Through practical and theoretical learning, they will distinguish between electrolysis of molten ionic compounds (e.g. aluminium oxide or lead bromide) and aqueous solutions (e.g. sodium chloride or copper sulfate), recognising how the products differ depending on the reactivity of the ions present.

The unit develops substantive knowledge by focusing on:

The definition of electrolysis as the decomposition of an ionic compound using electricity.

The movement of charged particles (cations and anions) and their attraction to oppositely charged electrodes.

The reactions at the cathode and anode, including the identification of products from ionic half-equations.

The industrial importance of electrolysis, such as the extraction of aluminium and the purification of copper.

The electrolysis of aqueous solutions, where water participates and affects which products are formed.

In parallel, the unit strengthens disciplinary knowledge by embedding the principles of working scientifically. Students will plan and carry out investigations, such as observing the electrolysis of copper sulfate or sodium chloride solution, recording their observations accurately, identifying gases formed, and linking these to theoretical predictions. Through these investigations, they refine their understanding of electrical conductivity, chemical decomposition, and oxidation-reduction processes in context.

The unit incorporates a range of Assessment for Learning (AfL) strategies to monitor and support student progress. These include retrieval practice of key ionic concepts, diagnostic questioning to address misconceptions (for example, that metals form at the cathode even in aqueous solutions), and scaffolded writing tasks to support the construction of balanced half-equations. Structured reflection tasks encourage students to explain patterns in terms of ion reactivity and electrode potential, reinforcing higher-order thinking.

Links to real-world contexts are made explicit throughout, connecting classroom learning to industrial and environmental applications. Examples include the electrolysis of brine in the manufacture of chlorine and sodium hydroxide, the process for aluminium extraction, and the use of electroplating in manufacturing. These case studies help students appreciate how electrolysis underpins modern chemical industries and sustainable technologies.

Supporting all learners, this unit is designed with accessible scaffolds, practical engagement, and stepwise progression. It enables students to confidently interpret ionic processes, write half-equations, and predict electrolysis products. Ultimately, the study of electrolysis consolidates prior learning about ions, charge, and reactivity while extending scientific understanding towards energy transformations, redox chemistry, and industrial chemical processes — preparing students for more advanced study in physical and inorganic chemistry.