GCSE Chemistry · AQA 8462 · Topic 4.8.1
Purity, formulations and chromatography
Key points
- In chemistry a pure substance contains only one element or compound. In everyday language 'pure' just means nothing has been added (e.g. 'pure' orange juice).
- Pure substances melt and boil at specific temperatures; impure substances melt over a range of temperatures, which can be used to check purity.
- A formulation is a mixture of components in carefully measured amounts to give a useful product, e.g. paints, cleaning agents, fuels, alloys and medicines.
- Paper chromatography has a stationary phase (the paper) and a mobile phase (the solvent). Substances separate depending on how they distribute between the two phases.
- Draw the start line in pencil and keep it above the solvent level. A pure substance gives one spot in every solvent; a mixture gives more than one.
- . values are always less than 1 and help identify compounds by comparison with known samples.
Topic notesPremium
Chemists use "pure" in a stricter way than adverts do, and they have practical ways to check purity. This sub-topic also covers formulations and how paper chromatography separates and identifies substances.
Unlock the full notes with Premium
Premium includes full topic notes, the paper generator, self-quizzes and progress tracking.
Practise this topicPremium
Premium members can generate an exam-style paper with a mark scheme, or take a quick quiz, on Purity, formulations and chromatography.