Chapter 19 Separating Mixtures

A mixture consists of two or more substances mingled together but not chemically combined.

Examples of mixtures:

Sea water = water + other substances dissolved in it (e.g. salt)

Crude oil = petrol, diesel, tar and lots of other substances

Air = oxygen, nitrogen, carbon dioxide and other gases

We can separate mixtures using a variety of techniques:

Example:

1. Filtration

Filtration is used to separate an insoluble solid e.g. sand or soil and a liquid e.g. water.It involves using a sieve or filter paper. Filter paper has tiny pores (holes) which allow tiny particles through but block larger particles.

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2. Evaporation

Evaporation is used to separate a soluble solid e.g. salt from a Liquid e.g. water. It involves heating the solution until the solvent e.g. water evaporates leaving

behind the solute e.g. the salt

Salt – which is mined from the ground is called rock salt. It is a mixture of salt, sand and gravel. It is spread on roads in winter to prevent them becoming icy.

3. Distillation – method of separation which can separate a soluble solvent e.g. salt from a solvent e.g. water or two miscible liquids (two liquids that mix) e.g. alcohol and water.

4. Chromatography

Paper chromatography can be used to

separate mixtures of substances which are in a solution. The different substances travel up the paper at different speeds.