A mixture is made from different substances that are not chemically joined.

For example powdered iron and powdered sulfur mixed together makes a mixture of iron and sulfur. They can be separated from each other without a chemical reaction, in the way that different coloured sweets can be picked out from a mixed packet and put into separate piles.

Mixture and compounds

Mixtures have different properties from compounds. The table summarises these differences.

	Mixture	Compound
Composition	Variable composition – you can vary the amount of each substance in a mixture.	Definite composition – you cannot vary the amount of each element in a compound.
Joined or not	The different substances are not chemically joined together.	The different elements are chemically joined together.
Properties	Each substance in the mixture keeps its own properties.	The compound has properties different from the elements it contains.
Separation	Each substance is easily separated from the mixture.	It can only be separated into its elements using chemical reactions.
Examples	Air, sea water, most rocks.	Water, carbon dioxide, magnesium oxide, sodium chloride.

An example - iron, sulfur and iron sulfide

Remember that iron and sulfur react together when they are heated to make a compound called iron sulfide. What are the differences between a mixture of iron and sulfur, and iron sulfide? Here are some of them:

• The mixture can contain more or less iron, but iron sulfide always contains equal amounts of iron and sulfur.

• The iron and sulfur atoms are not joined together in the mixture, but they are joined together in iron sulfide.

• The iron and sulfur still behave like iron and sulfur in the mixture, but iron sulfide has different properties from both iron and sulfur.

• You can separate the iron from the mixture using a magnet but this does not work for iron sulfide.