Mixtures and separation techniques

The five separation techniques

Each technique exploits one key physical difference between substances — find that difference and you've found your method.

1. 1FiltrationWorks because the solid is INSOLUBLE — its particles are too large to pass through the filter paper, so the liquid (filtrate) drains through while the solid remains.+
2. 2CrystallisationWorks because the solid is SOLUBLE — gently evaporating the solvent makes the solution saturated so pure crystals form; if the solid is less soluble when cool, cooling the saturated solution helps more crystals deposit.+
3. 3Simple distillationWorks because the solvent has a lower boiling point than the dissolved solid — heating vaporises the solvent, which is then condensed and collected as a pure liquid.+
4. 4Fractional distillationWorks because miscible liquids have DIFFERENT boiling points — the fractionating column allows each liquid to vaporise and condense at a different height, separating them.+
5. 5ChromatographyWorks because substances have DIFFERENT SOLUBILITIES in the solvent — more soluble substances are carried further by the moving solvent, so the mixture spreads into separate spots.+

Stop and think

Commit to an answer before you reveal — this is exactly the kind of question AQA asks.

A student has a mixture of two miscible liquids: ethanol (boiling point 78 °C) and water (boiling point 100 °C). Which technique should they use to separate them, and what physical property does it exploit?

Tap any cell to reveal it. Tap a column header to read one property down every item.