24.1 Electrolysis

Cambridge International A2 Level Chemistry (9701)

2026 Syllabus Objectives

By the end of this topic, you should be able to:

  1. Predict which substances are released during electrolysis, based on whether the electrolyte is molten or aqueous, the electrode potentials of the ions, and the concentration of the ions.
  2. State and apply the relationship F = Le, linking the Faraday constant (F), the Avogadro constant (L), and the charge on one electron (e).
  3. Calculate:
    • (a) The quantity of charge passed during electrolysis using Q = It
    • (b) The mass and/or volume of a substance released during electrolysis
  4. Describe how the Avogadro constant can be determined experimentally using an electrolytic method.

Main Content

https://cambridgeassistant.com

What Is Electrolysis?

Electrolysis is the process of using an electric current to break down a compound into simpler substances (its elements). The electric current forces a chemical reaction to happen that would not occur on its own.

For example, when zinc chloride (ZnCl₂) is broken down by electrolysis, it splits into zinc metal and chlorine gas:

ZnCl₂ → Zn + Cl₂

Electrolysis is commonly used to:

  • Extract metals from their ores when heating with carbon is not possible (e.g., aluminium from aluminium oxide)
  • Purify metals (e.g., purifying copper)
  • Produce non-metals such as fluorine

The Electrolysis Cell — How It Is Set Up

Electrolysis takes place inside an electrolytic cell, which contains the following components:

  • Electrolyte — the substance being broken down. It must be either a molten (melted) ionic compound or a concentrated aqueous solution (dissolved in water) of ions, so that ions are free to move and carry charge.
  • Electrodes — two solid rods (made of metal or graphite) that conduct electricity into and out of the electrolyte.
    • The anode is the positive (+) electrode. Negatively charged ions (anions) are attracted to it.
    • The cathode is the negative (−) electrode. Positively charged ions (cations) are attracted to it.
  • Direct current (DC) power supply — provides the electrical energy to drive the reaction.

💡 Memory tip: "Anode = Anions arrive" and "Cathode = Cations come"

Sign in to view full notes