Example 1
How could you recover dry salt from sand mixed with salt?
Add water to dissolve the salt, filter out insoluble sand, then evaporate water from the filtrate as the water leaves. The salt remains.
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Year 7
Choosing a separation method
Match filtration, sieving, magnetism, evaporation, distillation and chromatography to properties.
Method and worked examples
Match separation methods to property differences. Sieving uses particle size; magnets separate magnetic material. Filtration traps insoluble particles while fluid passes through. Evaporation can recover a dissolved non-volatile solid, leaving the solvent uncollected. Distillation vaporises the solvent, then condenses and collects it. Choose according to whether the wanted product is the solid or the solvent.
Chromatography separates suitable dissolved substances because they move different distances with a solvent and interact differently with the paper. Several separated coloured spots support several components. A salt-and-sand mixture needs a sequence: dissolve the salt, filter out sand, then recover salt from the filtrate by evaporation. One method rarely separates every possible mixture.
Example 1
Example 2
A community demonstration needs to collect water from a salt solution. Why is evaporation alone insufficient?
Evaporation lets water vapour escape. Distillation cools and condenses the vapour so the water can be collected.
Watch out: Each method targets particular property differences. A multicomponent mixture often requires several methods.