What does the Crude oil and organic chemistry module cover?

This module covers WJEC Unit 2 topic 2.5. It covers crude oil as a mixture of hydrocarbons and its separation by fractional distillation, the alkane and alkene homologous series and the test for unsaturation, combustion and cracking, alcohols and the production of ethanol, and addition polymerisation and the problems of plastic waste.

Which unit and paper assess this module?

These topics are part of Unit 2 (Chemical bonding, application of chemical reactions and organic chemistry), assessed on the Unit 2 written paper. The paper is 1 hour 45 minutes, worth 80 marks and 45 percent of the qualification, sat at Foundation or Higher tier.

What are the key formulae and tests to learn?

Learn the alkane general formula CnH2n+2 and the alkene general formula CnH2n, the bromine water test for alkenes, the complete and incomplete combustion products, and the repeat unit of an addition polymer.

Two ways. Fermentation uses yeast to convert sugars into ethanol and carbon dioxide in warm anaerobic conditions, using renewable material but giving a slow, dilute product. Hydration of ethene with steam and a catalyst is fast and gives pure ethanol but uses finite crude oil.

How should I revise this module?

Learn how fractional distillation separates crude oil and the trends down the column. Learn alkanes and alkenes, their formulae and the bromine water test. Understand cracking and why it is done. Compare the two routes to ethanol. Practise drawing polymer repeat units and discussing plastic waste. Use WJEC past papers.

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WJEC GCSE Chemistry: Crude oil and organic chemistry (Unit 2.5) overview

An overview of the Crude oil and organic chemistry module in WJEC GCSE Chemistry (topic 2.5), mapping crude oil and fractional distillation, alkanes and alkenes and cracking, alcohols and ethanol, and addition polymers and their disposal.

Generated by Claude Opus 4.87 min readWJEC Chemistry 2.5Updated 2026-06-14

Reviewed by: AI editorial process; not yet individually human-reviewed

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The topics in this module
How this module fits the exam
How to study this module

The Crude oil and organic chemistry module covers WJEC Unit 2 topic 2.5. It is the organic chemistry of the course: where our fuels come from, the families of carbon compounds, how ethanol is made, and how alkenes become the plastics we use every day. This page maps the module and links to a focused answer page for each part.

The topics in this module

Crude oil and fractional distillation: Crude oil as a finite mixture of hydrocarbons, and its separation by boiling point into fractions. See Crude oil and fractional distillation.
Alkanes, alkenes and cracking: The two homologous series, the bromine water test, combustion, and cracking large hydrocarbons. See Alkanes, alkenes and cracking.
Alcohols and ethanol: The alcohol series and the -OH group, and making ethanol by fermentation and from ethene. See Alcohols and ethanol.
Polymers and plastics: Addition polymerisation of alkenes, the repeat unit, polymer uses, and waste disposal. See Polymers and plastics.

How this module fits the exam

These topics sit in Unit 2, assessed on the Unit 2 written paper (1 hour 45 minutes, 80 marks, 45%). Questions test fractional distillation, alkane and alkene reactions and formulae, cracking equations, the routes to ethanol, and polymer repeat units and disposal.

How to study this module

Master fractional distillation. Separation by boiling point and the trends down the column.
Know the two families. Alkanes CnH2n+2, alkenes CnH2n, and the bromine water test.
Understand cracking. Breaking large molecules into smaller alkanes and useful alkenes.
Compare the ethanol routes. Fermentation (renewable, slow) versus hydration (finite, fast and pure).
Practise polymers. Draw repeat units and discuss the problems of plastic waste.

Then test yourself with the module quiz.

Sources & how we know this

WJEC GCSE Chemistry specification (from 2016) — WJEC (2016)