IGCSE Chemistry: Electrochemistry & Redox Guide

IGCSE Chemistry electrochemistry is a high-value topic where students lose easy marks predicting electrolysis products and writing half equations. This guide gives you one exam-ready walkthrough for both the Core and Extended tiers.

It covers Cambridge IGCSE Chemistry, codes 0620 and 0971, plus Edexcel International GCSE Chemistry, code 4CH1. You will learn to identify redox, apply the electrode rules, and balance half equations.

What is electrochemistry in IGCSE Chemistry?

Electrochemistry in IGCSE Chemistry is the study of electron transfer in redox reactions and the use of electricity to break compounds apart in electrolysis. It splits into two examinable halves.

Redox happens on its own, while electrolysis forces a reaction using an outside current.

The topic has two branches, and each shows up across both exam papers.

• Redox: electrons transfer on their own.
• Electrolysis: electricity forces the reaction.
• Both appear in Core and Extended.
• Questions carry several marks each.

This topic sits inside the wider IGCSE curriculum you revise across the year.

What are redox reactions in IGCSE Chemistry?

Redox reactions IGCSE revision starts with one rule. Oxidation and reduction always happen together, so you cannot have one without the other. Electrons move from the reducing agent to the oxidising agent.

According to the Royal Society of Chemistry, redox describes any reaction where electrons are transferred between species. Everyday examples include rusting, combustion, and metal displacement.

The oxidising agent gains electrons and is itself reduced. The reducing agent loses electrons and is itself oxidised. Naming the two agents correctly often earns a mark on its own.

How do you identify oxidation and reduction?

The quickest way is OIL RIG: Oxidation Is Loss of electrons, Reduction Is Gain. These oxidation and reduction notes also work with oxygen, hydrogen, and oxidation number, giving four clear tests you can apply to almost any equation.

Four working definitions let you spot each change fast.

• Oxidation loses electrons; reduction gains them.
• Oxidation gains oxygen; reduction loses it.
• Oxidation loses hydrogen; reduction gains it.
• Oxidation raises oxidation number; reduction lowers it.

To find the agent, ask which species caused the change in the other one.

What does OIL RIG mean?

OIL RIG is a simple memory aid. OIL means Oxidation Is Loss. RIG means Reduction Is Gain. Both refer to electrons. Say it once and you will rarely mix up the two changes again.

What are oxidation numbers?

Oxidation numbers are Extended-tier tools. They track how many electrons an atom appears to control. A rise means oxidation, and a fall means reduction, which lets you prove redox even when no oxygen is involved.

A few short rules cover almost every Extended question.

• Uncombined elements score zero.
• Simple ions equal their charge.
• Oxygen is usually minus two.
• Hydrogen is usually plus one.
• Group 1 metals are plus one.

How does electrolysis work?

Electrolysis breaks down a molten or aqueous ionic compound using a direct current. The liquid is the electrolyte. The negative electrode is the cathode, and the positive electrode is the anode.

Positive ions move to the cathode, while negative ions move to the anode.

Electrical energy drives a chemical change that would not happen on its own. Inert electrodes, often carbon or platinum, carry the current without joining in the reaction.

Why must the substance be molten or aqueous?

Ions must be free to move for a current to flow. In a solid, ions are locked in a fixed lattice and cannot travel. Melting or dissolving the compound frees the ions, so charge can move to each electrode.

What are the rules for electrolysis?

The electrolysis rules chemistry students need are short. At the cathode, the less reactive metal or hydrogen forms. At the anode, a halogen or oxygen forms. IGCSE Chemistry electrochemistry marks often depend on reading the table below correctly.

Examiner reports for IGCSE Chemistry regularly flag wrong electrode products as a common, avoidable error. Working through examples with a Cambridge IGCSE Chemistry tutor helps the pattern stick.

This table sums up what forms at each electrode using inert electrodes, so you can predict the products for common molten and aqueous compounds without guessing your way through exam questions.

Situation	Cathode product	Anode product
Molten ionic compound	The metal is deposited	The non-metal is released
Reactive metal, dilute solution	Hydrogen gas bubbles off	Oxygen gas bubbles off
Reactive metal, concentrated halide	Hydrogen gas bubbles off	The halogen is released
Unreactive metal salt solution	The metal is deposited	Oxygen or the halogen forms
Copper(II) chloride solution	Copper coats the cathode	Chlorine gas forms

In short, the cathode follows metal reactivity. The anode depends on the negative ion and how concentrated the solution is.

What forms at the cathode?

At the cathode, positive ions gain electrons, so reduction happens here. If the metal is more reactive than hydrogen, hydrogen forms instead. If the metal is less reactive than hydrogen, the metal itself is deposited.

What forms at the anode?

At the anode, negative ions lose electrons, so oxidation happens here. A concentrated halide solution releases the halogen, such as chlorine. A dilute solution usually releases oxygen from the water instead.

How do you write half equations?

A half equation shows the change at one electrode only. You balance the atoms first, then add electrons so the charges match. Electrons go on the right for oxidation and on the left for reduction.

Follow four steps and the equation almost writes itself.

1. Write the ion and its product.
2. Balance the main atoms.
3. Add electrons to balance the charge.
4. Check: cathode gains, anode loses.

For example, at an aluminium cathode: Al³⁺ + 3e⁻ → Al. At the anode: 2O²⁻ → O₂ + 4e⁻. The electrons cancel when you combine both halves.

Where is electrolysis used in real life?

Electrolysis powers several industries you meet at IGCSE. It extracts aluminium from its oxide, produces chlorine and hydrogen from brine, purifies copper, and electroplates metals for protection or looks.

Aluminium oxide is dissolved in molten cryolite to lower the melting point before electrolysis. According to the International Aluminium Institute, smelting uses about 14 kilowatt hours of electricity for every kilogram of aluminium produced.

Brine electrolysis gives chlorine at the anode, hydrogen at the cathode, and sodium hydroxide in the solution. Copper is purified using active electrodes, where the impure anode dissolves and pure copper coats the cathode.

You can revise these processes with an Edexcel International GCSE Chemistry tutor if a board-specific example trips you up.

What is your next step in electrochemistry?

IGCSE Chemistry electrochemistry rewards three habits: spot redox with OIL RIG, apply the electrode rules, and write balanced half equations. Remember which parts are Extended only, such as oxidation numbers and half equations.

Now turn understanding into marks. Work through timed past papers on redox and electrolysis, and review any product or half equation you get wrong until the pattern feels automatic.