MATTER AND ENERGY

2.4 - Classification of Matter

2.4.2 - Mixtures

A mixture is a combination of two or more substances in which each substances's identity is retained. Mixtures are subdivided into two categories: homogeneous mixtures and heterogeneous mixtures.

Homogeneous mixtures are solutions which have uniform composition and appearance throughout. A solution may be gaseous (eg - air), solid (eg - brass) or liquid (eg - seawater). If a spoonful of sugar is dissolved in a glass of water, the composition of the sugar solution becomes the same in the glass. The sugar will not settle out and every spoonful of sugar solution that is removed from the glass will have the same composition. If the water in the glass is evaporated to dryness, the sugar retains its identity and can be recovered.

Heterogeneous mixtures are mixtures that do not have uniform composition and appearance throughout. The individual components which make up the mixture remain physically separated and can be seen as separate components. If a spoonful of sand is introduced in a glass of water, even after considerable stirring, the sand will settle to the bottom of the glass. Visually, the sand will separate out and the composition of sand in the glass will be the greatest at the bottom of the glass. Any attempts to withdraw spoonfuls of sand and water will have varying composition of each substance.

Section 3.2
Composition and Properties of Matter ..p52

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