Elements, compounds and Mixtures
Another method of classification of matter is based on its composition. A substance is matter that has a definite or constant composition and has distinct properties. Examples are aluminium sliver, water, carbon dioxide, nitrogen, oxygen etc. Substances differ from one another in composition and can be identified by their properties like colour, smell, taste, appearance, etc. Aluminium has uniform composition. Similarly water has uniform composition. No doubt there are also matter which do not have uniform composition. Such matter are called mixtures. Some examples of mixtures are air, soft drink, milk, and cement. Mixtures are either homogeneous or heterogeneous. Suppose you add 5g of sugar to water kept in a glass tumbler. After stirring, the mixture obtained is uniform through out. This mixture is homogeneous through out and is called solution. Air is solution of several gases (oxygen, nitrogen, water vapour, carbon dioxide etc). Suppose you mix sand with iron filings, sand grains and the iron filings remain visible and separate. This type of mixture in which the composition is not uniform, is called a heterogeneous mixture. If you add oil to water, it creates another heterogeneous mixture because the liquid thus obtained does not have a uniform composition.