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Separation Techniques

Year 7 🌿 Materials & Environment Describe filtration, evaporation, distillation and chromatography.

Filtration separates an insoluble solid from a liquid. The solid stays on the filter paper (residue); the liquid passes through (filtrate).

Use: Separating sand from water, separating a precipitate from solution.

To recover a dissolved solid from solution: heat until most water evaporates, then cool to allow crystals to form.

Use: Obtaining salt (NaCl) from salt water. Evaporation to dryness gives salt directly; crystallisation gives purer, larger crystals.

Distillation separates liquids with different boiling points. Chromatography separates a mixture using different rates of travel through a medium.

Rf Value (Chromatography)

$$R_f = \frac{\text{distance moved by spot}}{\text{distance moved by solvent front}}$$

Rf values range from 0 to 1. Each compound has a unique Rf in a given solvent — used to identify substances.

🎯 Ready to test yourself? Click the Quiz tab above to practise questions on this topic!

🎬 Interactive Demonstration — Separation Techniques

Choose the best separation technique for each mixture.

Select the correct technique.

⚗️ 🔬 Rf Value Calculator

Calculate Rf values from paper chromatography data.

Distance moved by spot (cm)

Distance moved by solvent (cm)