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.
There are times when the purity of a substance is very important. For example, a medicine must not contain any harmful chemicals.
Mixtures have different properties from compounds. The table summarises these differences.
|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 which are 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|
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: