Mixtures

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

There are 3 main differences between a compound and a mixture are:

Compounds     

~Compounds have a fixed composition.

~Chemical reactions must be used to separate the elements in a compound.

~There are chemical bonds between the atoms of different elements in componds.

Mixtures

~Mixtures have no fixed composition.

~Different compounds or elements can be separated again.

~There are no chemical bonds between atoms of different substances in a mixture.

Because a mixture has no chemical bond between the substances in a mixture, they can be separated easily.

They can be separated physically - they do not involve chemical reactions and no new substances are formed.

The chemical properties of each substance in the mixture are unchanged.

Here are some separation techniques:

Chromatography

This is good for separating dissolved substances in solution that have different colours , such as links and plant dyes.It works because some of the coloured substances dissolve in the liquid better than others , so they travel futher up the paper.

Filtration

This is used to separate insoluble solid from a liquid. (An isoluble substance cannot dissolve.) E.g  A mixture of sand and water.

Evaporation

This good for separating a liquid from a solution and a soluble soild from a liquid.(A soluble does dissolve.) E.g Copper Sulphate crystals can be separated from copper sulphate.

Simple Distillation

This is when water evaporates from a solution , but is cooled and condensed in a different beaker, the solvent is also collected. Unlike evaporation the gas is not released into the atomosphere.

Fractional Distillation

Used to separate two or more miscible liquids from each other as the liquids have different boiling points.E.g Ethanol can be separated from a mixture of ethanol and water by frational distillation.

Crystallisation

The solution is placed over a water bath instead of the bunsen burner like in evaporation.This is a more gente way of heating the crystals.

As soon a the cystals appear on the edge you'll have to stop heating the solution, the rest of the solution will evaporate by itself at room temperature.