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Separating mixtures
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Mixtures can be separated because their parts have different properties. Choosing the right method is a common exam question.
Pure substances and mixtures
In chemistry, a pure substance contains only one element or one compound.
Pure substances melt and boil at a sharp, fixed temperature. Mixtures melt over a range.
Pure substances melt and boil at a sharp, fixed temperature. Mixtures melt over a range.
Choosing a method
Match the method to the mixture.
How distillation works
The mixture is heated. The liquid with the lowest boiling point evaporates first. The vapour is cooled in a condenser and collected as a liquid.
How would you get pure water from sea water?
- Sea water is a solution of salt in water.
- You want the solvent (water), not the solid.
- Use simple distillation: boil, then condense the steam.
Answer: Simple distillation
Filtration for insoluble solids, crystallisation for a dissolved solid, simple distillation for the solvent, fractional distillation for mixed liquids.
The interactive lesson includes the diagrams for this topic.
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