States of matter
Solid — particles close together in a regular pattern, vibrating in fixed positions.
Liquid — particles close together but irregular, sliding past each other.
Gas — particles far apart, moving fast and randomly.
During a change of state, the temperature stays the same. The energy is used to overcome the forces of attraction between particles (or is released when they form), rather than to increase the particles' kinetic energy.
Pure or impure?
A pure substance melts at one sharp temperature.
An impure substance melts over a range of temperatures, lower than the pure substance.
Separation techniques
| Technique | Separates |
|---|---|
| Filtration | An insoluble solid from a liquid |
| Evaporation / crystallisation | A dissolved solid from a solution |
| Simple distillation | A liquid from a solution, or liquids with very different boiling points |
| Fractional distillation | Liquids with similar boiling points |
| Chromatography | Soluble substances in a mixture |