'Pure' has a specific meaning in chemistry.
A pure substance is a single element or compound not mixed with any other substance.
A mixture contains two or more different substances mixed together, usually easy to separate.
|Diamond only contains the element carbon.||Air is a mixture of oxygen, carbon dioxide, nitrogen and other trace gases.|
|Water only contains the compound water.||Mineral water is a mixture of water and dissolved salts.|
|Table salt only contains the compound sodium chloride.||Milk is a mixture of water, lactose, fat and minerals such as salt.|
Here are some examples of pure substances and mixtures.