We know all the matter around is not pure. If we observe some soil (Mitti) and some surge placed on two different sheets of paper with a magnifying glass, we find soil contains clay particles, some grass particles and even some dead insects etc. That is soil particles of different kinds is called an impure substance.

Type of matter : -

On the basis of chemical nature, matter can be classified into two types :

(i) Pure substance. (ii) Impure substance (mixture)

(i) Pure substance :- A homogeneous material which contains particles of only one kind has a definite set of properties, is called a pure substance .

OR

A pure substance is a distinct type of matter that can not be separated into other matter by any physical process eg. oxygen, sulphur, iron etc. are pure substance however, if a substance is composed of two or more different kinds of particles combined together in fixed proportion by weight, then the substance is also regarded as pure substance. e.g. Sodium chloride is a pure substance, because it has a fixed number of sodium and chloride ions, combined together in fixed proportion by weight, Similarly, magnesium oxide (MgO), Carbon dioxide, copper sulphate etc. are pure substance.

(ii) Mixture :- When two or more substance (elements, compounds or both) are mixed together in any proportion, such that they do not undergo any chemical change, but retain their individual characteristics, the resulting product is called a mixture. e.g. Brass is mixture of copper and zinc.