Chemistry · 12.4 Separation & purification · Paper 5/6
Separation & Purification. Pick the method.
Four core techniques: filtration, crystallisation, simple distillation and fractional distillation. See the apparatus, what each one separates, and choose the right method for a given mixture.
0620 Topic 12.4 — Separation
filter · crystallise · distil
Paper 5/6 — Practical
This technique
Separates
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Based on
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Example
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Which method? — match the mixture
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📋 The four techniques
- Filtration — separates an insoluble solid from a liquid. The solid stays on the filter paper (residue); the liquid passes through (filtrate).
- Crystallisation — obtains a soluble solid from its solution. Evaporate to the point of crystallisation, then cool slowly so crystals grow.
- Simple distillation — separates a solvent from a solution (e.g. pure water from salt water). The liquid boils, the vapour condenses in the Liebig condenser.
- Fractional distillation — separates miscible liquids with different boiling points (e.g. ethanol from water) using a fractionating column.
⚠ Key points & precautions
- In distillation, the thermometer bulb sits at the side-arm to read the vapour temperature.
- Cooling water enters the condenser at the bottom (counter-current) for efficient condensing.
- Crystallise — do not evaporate to dryness, or you spoil the crystals.
- The fractionating column gives repeated evaporation/condensation so the more volatile liquid reaches the top first.
🎯 Syllabus reference (0620)
- 12.4 Separation & purification — describe and explain filtration, crystallisation, simple and fractional distillation, and choosing the right technique; identify residue and filtrate.