Separation and purification
Choosing a separation method
| Method | Separates |
|---|---|
| filtration | an insoluble solid from a liquid |
| crystallisation | a soluble solid from its solution |
| simple distillation | a solvent (liquid) from a solution |
| fractional distillation | two liquids with different boiling points |
Practice
Match each method to what it separates.
Filtration removes insoluble solids; crystallisation recovers a dissolved solid; fractional distillation separates liquids by boiling point.
Practice
To separate sand (insoluble) from water you would use:
Filtration removes an insoluble solid; the sand stays as residue and the water passes through.
Checking purity
- A pure substance melts and boils at sharp, fixed temperatures.
- Impurities lower the melting point and raise the boiling point.
Practice
Impurities lower the melting point and raise the boiling point of a substance.
A pure substance has sharp fixed melting and boiling points; impurities widen and shift them.
You've got it
Key idea
- filtration (insoluble solid + liquid), crystallisation (soluble solid), distillation (liquids)
- fractional distillation separates liquids by boiling point
- purity check: a pure substance has sharp fixed melting/boiling points