What are impure substances?????

Plzzz answer!!!!!!.

A substance is said to be impure if it has particles of other substance mixed in it. Mixtures are impure substances as they contain two or more substances present in any ratio. Mixtures are further classified as homogeneous and heterogeneous.

1. Homogeneous mixtures are those which have a uniform composition throughout. A solution of salt and water is an example of homogeneous mixture .
2. Heterogeneous mixtures are those which do not have a uniform composition throughout. A solution of water and chalk powder is an example of heterogeneous mixture.

The physical properties such as melting point of impure substances will always be different from pure substances.