Question

Difference between :

(a) Pure and impure substances

(b) Homogeneous and heterogeneous substances

Answer 1

Part (a)

Pure substances:

• Pure substances have definite composition and definite physical and chemical properties.​
• Pure substances are all homogeneous i.e. their composition is uniform throughout the bulk.
• Pure substances have sharp melting and boiling points.
• Examples: Elements and compounds.

Impure substances:

• Impure substances are made up of two or more pure substances mixed together in any proportion.
• They may be homogeneous or heterogeneous i.e. their composition is not uniform throughout the bulk.
• They are all mixtures.
• Examples: air, seawater, petroleum, and a solution of sugar in water are all impure substances.

Part (b)

A homogeneous mixture is a mixture where the components that make up the mixture are uniformly distributed throughout the mixture.
Example: Air, Sugar water, Rainwater.
A heterogeneous mixture is a mixture, where the components of the mixture are not uniform or have localized regions with different properties.
Example: Cereal in milk, Vegetable soup.