1.3 Separating Mixtures

A mixture is made up of two or more substances (elements or compounds) that are not chemically combined together

The ratio of elements present is always the same in any particular compound

• Compounds have a fixed composition • Mixtures have no fixed composition (the proportions vary depending on the amount of each substance mixed together)

• Compounds: chemical reactions must be used • Mixtures: different elements or compounds can be separated more easily (by physical means using the properties of each substance)

• Filtration • Crystallisation • Distillation • Chromatography

To separate substances that are insoluble in a particular solvent from those that are soluble in the solvent (eg sand and salt)

• Strain the solvent and its insoluble substance using filter paper • Sand that is collected on the filter paper can be washed with distilled water to remove any salt solution • Wet sand dried in a warm oven to evaporate any water left off and leave pure, dry sand

To separate a soluble substance from a solvent (eg salt from water)

• Heat the salt solution on a water bath • Stop heating at the point of crystallisation (when small crystals appear at the edge of the solution) • Rest of the water is left to evaporate at room temperature to get a good sample of salt crystals

To separate a soluble solid from a solvent (but when you need to collect the solvent instead of letting it evaporate)

• Solution is heated and boiled to evaporated the solvent • Outer glass tube with water flowing through acts as a cooler for the hot vapour in the inner tube. the hot vapour is cooled and condensed back into a liquid for collection in a receiving vessel