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Learn0620Papers 2, 4 · ExtendedExperimental techniques and chemical analysisSeparation and purification
Experimental techniques and chemical analysis · Subtopic 1 of 3

Separation and Purification

Choose apparatus for precision: a burette or pipette for accurate volumes, a gas syringe for gas volumes, a balance for mass. Choose a separation method from the properties of the mixture: filtration removes an insoluble solid from a liquid; crystallisation gets a soluble solid from its solution; simple distillation gets a solvent from a solution; fractional distillation separates miscible liquids with different boiling points; chromatography separates dissolved substances such as dyes.

Cambridge 5070 Paper 1Cambridge 5070 Paper 2Cambridge 0620 Papers 2, 4Cambridge 0620 Papers 1, 3Edexcel 4CH1 Paper 1CEdexcel 4CH1 Paper 2C≈ 35 minRevision 1 · updated 2026-10-30
Section 1 of 14

Learning objectives

  • Choose apparatus to measure time, temperature, mass and volume.
  • Use the terms solvent, solute, solution, residue and filtrate.
  • Describe and choose filtration, crystallisation and distillation.
Pause and think

How could you get pure drinking water from sea water using only kitchen equipment?

Section 2 of 14

Core idea

Start herePure from impure

Almost nothing in nature is pure. Every medicine, every drop of tap water and every sample in a lab has been through some separation step.

The big idea

The best separation method depends on the properties that differ: solubility, boiling point or particle size.

1. Choosing a method

Separation decision tree

Ask what you have and what you want.

Worked exampleA three-part mixture

A mixture contains sand, salt and water.

Goal
Obtain all three.
Strategy
Separate in a logical order.
  1. filter⇒sand\text{filter}\Rightarrow\text{sand}
    Sand is the residue.
  2. distil filtrate⇒water\text{distil filtrate}\Rightarrow\text{water}
    Water evaporates and condenses.
  3. residue in flask⇒salt\text{residue in flask}\Rightarrow\text{salt}
    Salt remains (or crystallise part of the filtrate).
AnswerFilter, then distil.
✓ CheckEach component collected ✓.
Key takeawayPrecision Burette and pipette for accurate volumes; measuring cylinder for rough volumes; gas syringe for gases.
Pause and think

Why is a fractionating column packed with glass beads?

Summary

  • Filter: insoluble solids.
  • Crystallise: dissolved solids.
  • Distil: solvents and liquid mixtures.
Key words
Residue
Solid left in the filter paper.
Filtrate
Liquid that passes through a filter.
Miscible
Liquids that mix completely.
HistoryAlembic. Distillation was refined by medieval Arab chemists such as Jabir ibn Hayyan, who designed the alembic still. Words like "alcohol" and "alkali" come from Arabic.
Fun factGases from air. Liquid air is fractionally distilled to give nitrogen, oxygen and argon. Nitrogen boils first at −196 ∘C-196\,^\circ\mathrm{C}.
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