GCSE Chemistry · AQA 8462 · Topic 4.8
Chemical analysis
Key points
- A pure substance is a single element or compound; it melts and boils at a fixed, sharp temperature. Impurities change these values.
- Formulations are carefully designed mixtures, such as paints, fuels, medicines and fertilisers.
- Paper chromatography separates and identifies substances using a stationary phase and a mobile phase; = distance moved by substance ÷ distance moved by solvent.
- Tests for gases: hydrogen (squeaky pop), oxygen (relights a glowing splint), carbon dioxide (limewater turns milky), chlorine (bleaches damp litmus paper).
- (Chemistry only) Flame tests, sodium hydroxide precipitates and other tests identify metal ions and negative ions.
- (Chemistry only) Instrumental methods such as flame emission spectroscopy are accurate, sensitive and fast.
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Chemical analysis is about answering two questions: is this substance pure, and what is in it? Analysts in forensic labs, hospitals and water companies use the same ideas you learn here, from simple test-tube tests to fast instrumental…
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