Edexcel GCSE Chemistry Topic 9 Separate chemistry 2: a complete overview

What Topic 9 actually demands

Separate chemistry 2 is sat only by students taking GCSE Chemistry as a separate science. It covers practical qualitative analysis, the organic chemistry of alcohols and carboxylic acids, and polymers and materials. Edexcel tests precise test results and observations, the functional groups and reactions, and clear comparison of materials and their life cycles.

This guide walks through the topic in specification order, then sets out the exam patterns Edexcel repeats. Each dot point has a matching page with practice questions; this overview ties them together.

Qualitative analysis

Metal cations are identified by flame tests (lithium red, sodium yellow, potassium lilac, calcium orange-red, copper blue-green) and by sodium hydroxide precipitates (copper blue, iron(II) green, iron(III) brown, calcium and aluminium white, with aluminium hydroxide redissolving in excess). Anions are tested by: carbonate fizzing with acid; sulfate giving a white precipitate with acidified barium chloride; and halides giving white, cream or yellow precipitates with acidified silver nitrate. An unknown salt is identified by testing the cation and the anion separately.

Alcohols and carboxylic acids

The alcohols ($-OH$) include ethanol, made by fermentation of sugar with yeast. Alcohols burn to carbon dioxide and water, form neutral solutions, and are oxidised to carboxylic acids. The carboxylic acids ($-COOH$) include ethanoic acid; they are weak acids and react with metals, bases and carbonates (fizzing to give carbon dioxide).

Polymers and materials

Addition polymerisation joins alkene monomers into one long chain with no by-product; the repeating unit shows the opened double bond with extending bonds. Condensation polymerisation releases a small molecule such as water. Polymers are cheap, light and mouldable but often not biodegradable. Ceramics, composites and metals suit different uses by their properties. A life cycle assessment weighs the environmental impact of a product from raw materials to disposal, and can be subjective.

How Topic 9 is examined

A typical Edexcel profile for this topic:

• Tests for ions. Describing tests and results, and identifying an unknown salt.
• Organic reactions. Functional groups and the reactions of ethanol and ethanoic acid.
• Polymerisation. Explaining addition polymerisation and drawing repeating units.
• Materials and LCA. Comparing materials and evaluating a life cycle assessment.

Check your knowledge

A mix of recall and application questions covering Topic 9. Attempt them under timed conditions, then check against the solutions.

1. State the flame colour for sodium and for copper. (2 marks)
2. Describe the test for carbonate ions and the positive result. (2 marks)
3. A metal ion gives a blue precipitate with sodium hydroxide. Identify the ion. (1 mark)
4. State the functional group of the alcohols and of the carboxylic acids. (2 marks)
5. Name the product when ethanol is oxidised. (1 mark)
6. Explain what is meant by addition polymerisation. (2 marks)
7. Give one reason why many polymers are difficult to dispose of. (1 mark)
8. Name the four stages of a life cycle assessment. (2 marks)