Chemical analysis - (CCEA)
Most elements are rarely found in their pure form. They are found chemically combined with other elements in compounds. Compounds are often found mixed with other compounds. Mixtures may be separated and analysed.
Pure substances
'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.
| Pure substances | Mixtures |
|---|---|
| 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.