We see mixtures all the time in our everyday lives. A stew, for example, is a mixture of different foods such as meat and vegetables; sea water is a mixture of water, salt and other substances, and air is a mixture of gases such as carbon dioxide, oxygen and nitrogen.

Definition: Mixture

A mixture is a combination of two or more substances, where these substances are not bonded (or joined) to each other and no chemical reaction occurs between the substances.

In a mixture, the substances that make up the mixture:

  • are not in a fixed ratio

    Imagine, for example, that you have \(\text{250}\) \(\text{mL}\) of water and you add sand to the water. It doesn’t matter whether you add \(\text{20}\) \(\text{g}\), \(\text{40}\) \(\text{g}\), \(\text{100}\) \(\text{g}\) or any other mass of sand to the water; it will still be called a mixture of sand and water.

  • keep their physical properties

    In the example we used of sand and water, neither of these substances has changed in any way when they are mixed together. The sand is still sand and the water is still water.

  • can be separated by mechanical means

    To separate something by “mechanical means”, means that there is no chemical process involved. In our sand and water example, it is possible to separate the mixture by simply pouring the water through a filter. Something physical is done to the mixture, rather than something chemical.

We can group mixtures further by dividing them into those that are heterogeneous and those that are homogeneous.

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