Everything on the GCSE Chemistry Separation Techniques poster is written out below, section by section. Use it to search the sheet, copy parts into your own notes, or check a fact quickly.
Filtration
Filtration separates an insoluble solid from a liquid. The mixture is poured through filter paper in a funnel.
- The solid stays on the paper as the residue.
- The liquid passes through as the filtrate.
Example: separating sand from water.
Crystallisation
Crystallisation recovers a soluble solid from a solution.
- Gently heat the solution in an evaporating basin until concentrated.
- Leave to cool so crystals form.
- Filter and dry.
Example: obtaining salt from salt water.
Simple distillation
Simple distillation separates a solvent from a dissolved solute - for example, pure water from salt water.
- Heat the solution so the solvent evaporates.
- The vapour rises and condenses in the Liebig condenser, then is collected in the receiving flask.
- Only works when the boiling points of the substances are very different.
Apparatus: Bunsen burner, thermometer, Liebig condenser, receiving flask.
Fractional distillation
Fractional distillation separates two or more miscible liquids with different boiling points - for example, ethanol from water.
- A fractionating column (packed with glass beads) creates a temperature gradient from hot at the bottom to cool at the top.
- The liquid with the lowest boiling point reaches the top first and is collected.
Apparatus: Bunsen burner, fractionating column, thermometer, Liebig condenser, receiving flask.
Example: separating ethanol from water.
Paper chromatography
Paper chromatography separates dissolved substances by how they distribute between the stationary phase (paper) and the mobile phase (solvent).
- Pencil a line on the paper.
- Spot the sample on the line.
- Stand the paper in a beaker of solvent - below the pencil line so the spots are not washed away.
Pure substances give one spot in every solvent.
The R_f value identifies each substance:
R_f = distance moved by spot ÷ distance moved by solvent
R_f is always between 0 and 1.
Example: if a spot moves 3.0 cm and the solvent front moves 7.5 cm, R_f = 3.0 ÷ 7.5 = 0.40.