OCR Gateway GCSE Chemistry A: Predicting and identifying reactions and products (C4) overview
An overview of the Predicting and identifying reactions and products topic (C4) in OCR Gateway GCSE Chemistry A (J248), mapping the reactivity series and displacement, extracting metals and predicting reactions, flame and gas tests, tests for negative ions, and instrumental and chromatographic analysis.
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Topic C4 Predicting and identifying reactions and products of OCR Gateway GCSE Chemistry A (specification J248) is about using chemistry to predict what will react and to identify what is present. It covers the reactivity series and displacement, extracting metals, and the chemical tests and analytical methods used to identify substances. This page maps the topic and links to a focused answer page for each part.
The predicting and identifying topics
- The reactivity series and displacement (C4.1)
- The order of metal reactivity, the reactions of metals with water, oxygen and acids, displacement reactions, and predicting reactions. See The reactivity series and displacement.
- Predicting and extracting metals (C4.1)
- Metal ores and oxidation, extracting metals by reduction with carbon or by electrolysis, the role of carbon in the reactivity series, and predicting Group 1 and Group 7 reactions. See Predicting and extracting metals.
- Tests for cations and gases (C4.2)
- Flame tests for metal ions, identifying metal ions with sodium hydroxide, and the tests for hydrogen, oxygen, carbon dioxide, chlorine and ammonia. See Tests for cations and gases.
- Tests for anions (C4.2)
- The carbonate test with acid, the halide test with silver nitrate, and the sulfate test with barium chloride, with observations and ionic equations. See Tests for anions.
- Instrumental analysis and chromatography (C4.2)
- Paper chromatography and Rf values, the advantages of instrumental methods, and flame emission spectroscopy. See Instrumental analysis and chromatography.
How this topic is examined
Topic C4 is assessed on Paper 2 (Foundation, J248/02) or Paper 4 (Higher, J248/04), alongside topics C5, C6 and the C7 practical skills, assuming knowledge of C1 to C3. Each paper is 1 hour 45 minutes, worth 90 marks and 50% of the GCSE. Questions include predicting reactions, recalling tests and their results, writing ionic equations, calculating Rf values, and explaining instrumental methods. The chemical tests and chromatography are part of the C7 practical skills.
How to study the predicting and identifying topic
- Work from the specification statements. Each numbered point is a checklist; questions are written from them.
- Learn the reactivity series and displacement rule. They let you predict reactions and explain extraction methods.
- Memorise the tests. Flame colours, hydroxide precipitate colours, gas tests, and carbonate, halide and sulfate tests are reliable marks if learned precisely.
- Practise the ionic equations. The halide and sulfate precipitate equations come up often.
- Drill Rf calculations and instrument advantages. Know why instrumental methods beat simple tests. Use OCR past papers.
For the official specification
OCR publishes the full specification (J248), past papers and mark schemes at ocr.org.uk. Always revise from the current specification and OCR's own past papers, because question style is board-specific.