GCSE Combined Science — AQA

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Electrolysis · Aluminium extraction · Reactivity series · Acids & alkalis · Copper(II) sulfate · Displacement

Overview

Concise revision material for AQA Combined Science (GCSE). Use the diagrams linked below and, if you want printable PDFs, open this page in a browser and use Print → Save as PDF.

Electrolysis

Electrolysis uses electricity to decompose ionic substances. For molten salts: cations move to the cathode (reduced) and anions to the anode (oxidised). For aqueous solutions, H+/OH− must be considered.

Simple labelled diagram of an electrolysis cell with two electrodes in liquid, connected by wires.
Electrolysis cell diagram
Molten ionic compound example: molten NaCl → Na (cathode) and Cl2 (anode). In aqueous solutions, hydrogen may be produced at the cathode if the metal is more reactive than hydrogen.

Aluminium extraction — Hall–Héroult

Aluminium oxide (Al2O3) is dissolved in molten cryolite and electrolysed. Aluminium forms at the cathode, oxygen forms at the anode and reacts with carbon anodes to produce CO/CO2. The process is energy intensive.

Annotated diagram showing the Hall-Héroult cell for aluminium extraction with carbon anode, cathode, and molten mixture.
Hall–Héroult cell — Wikimedia Commons
Industrial safety note: high temperatures and CO/CO2 production — conceptual study only for schools.

Reactivity series & displacement

The reactivity series ranks metals by their tendency to form positive ions. More reactive metals will displace less reactive metals from their compounds.

Chart listing metals in order of reactivity from potassium (most reactive) down to gold (least reactive).
Reactivity series — Wikimedia Commons
Example: Zn + CuSO4 → ZnSO4 + Cu (zinc displaces copper).

Acids & alkalis

Key reactions: acid + metal → salt + hydrogen; acid + metal carbonate → salt + water + CO2; neutralisation: H+ + OH− → H2O. Test CO2 with limewater.

Diagram showing an acid and base mixing to produce water and salt in a reaction vessel.
Neutralisation — Wikimedia Commons

Preparing copper(II) sulfate (CuSO4)

Typical method: react copper oxide or carbonate with dilute sulfuric acid, filter off excess solid, gently evaporate and allow to crystallise blue CuSO4·5H2O.

Close-up photo of vibrant blue copper sulfate crystals on a white surface.
Copper(II) sulfate crystals — Wikimedia Commons
Wear goggles and gloves; follow school practical safety procedures.

Quick self-check quiz

  1. During the electrolysis of molten sodium chloride, what is produced at the cathode?
  2. Which gas is formed when an acid reacts with a metal carbonate?
  3. Which metal will displace copper from copper(II) sulfate: magnesium, silver or gold?
  4. In the Hall–Héroult process, what happens to carbon anodes?
  5. Write the products of neutralisation between hydrochloric acid and sodium hydroxide.
Answers
  1. Sodium metal.
  2. Carbon dioxide (CO2).
  3. Magnesium.
  4. They are oxidised to CO/CO2 (consumed).
  5. Sodium chloride and water (NaCl + H2O).