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Substances


SUBSTANCES


  • Matter is made up of one or more components known as substances. In terms of science, a substance is a kind of matter which cannot be separated into any other types of matter by physical means. Such a substance which has only one component and nothing else in it is called pure substance. Substances mostly mix with one another and their combination is known as mixture.

 

Pure Substances:

  • A pure substance means a single substance (or matter) which cannot be separated into other kinds of matter by any physical process.
  • A pure substance is made up of only one kind of atoms.

For example:

  • Metals like gold, silver, copper, Iron, tin in completely pure form are pure substances.
  • Ghee or Oil is not a pure substance because it is a mixture of many substances. Air is also not a pure substance as number of gases like oxygen, carbon dioxide, water vapours etc. are present in it.

 

Characteristics of Pure Substances:

  • A pure substance is homogeneous throughout its mass.
  • A pure substance cannot be separated into other kinds of matter by any physical process.
  • A pure substance has a fixed composition as well as a fixed melting point and boiling point.

 

Impure Substances: Mixture:

  • A mixture is the combination of two or more substances (elements or compounds) which do not combine chemically with each other and may be present in any proportion.

For example:

  • Salt solution is a mixture of two pure substances: salt and water, sugar solution is also a mixture, air is a mixture of different gases; milk is also a mixture etc.

 

Characteristics of Impure Substances:

  • A mixture may be homogeneous or heterogeneous.
  • A mixture can be separated into other kinds of matter by physical processes.
  • A mixture does not have a fixed composition or a fixed melting point and boiling point.
  • Most of the matter around us exists as mixture of two or more pure substances.
  • Pure substances are classified into two types –

Elements

Compounds