forces of attraction
Purity substances
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Most materials that we use are mixtures, and just a few are pure elements or pure compounds.
In chemistry, a pure substance is a single substance made of only one type of particle.
Impurities change the temperature at which a substance melts and boils.
dissolving
crystillisation
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A solution is made when a solute dissolves into a solvent.
If a substance can dissolve into a solvent, it is soluble. If it cannot dissolve, it is described as insoluble.
Heating, stirring and using fine powders are all ways to speed up dissolving.
filtration
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Filtration is used to separate an insoluble solid from a pure liquid or a solution.
Filtration usually involves a circle of filter paper folded to make a cone and placed into a filter funnel.
The filtrate is the liquid which passes through the filter paper and the residue is the solid left on the filter paper.
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Evaporation occurs when a liquid slowly turns into a gas below its boiling point.
Crystallisation is a separation technique used to obtain crystals of a solid solute.
When a solution is heated, the solvent evaporates and crystals of the solute are left behind.
chromotography
distillation
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Chromatography is a separation technique used to separate mixtures of soluble substances.
These are often coloured substances such as food colourings, inks, dyes or plant pigments.
Chromatograms can be used to match known pigments with those in a mixture.
On a chromatogram, one spot means that the substance is pure. An impure substance produces two or more spots.
Distillation is a separation technique used to separate a solvent from a mixture. For example, water can be separated from salt solution by distillation.
Distillation involves boiling the mixture and then condensing the gas to produce a liquid.