Question

We sometimes tell about "pure air'. But in reality air is not a pure substance. It is a mixture. Give
reasons.​

Answer 1

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Air is a mixture because:

(i) The properties of the constituents of air (oxygen, nitrogen, carbon dioxide etc.) are not changed. For example, pure oxygen is a supporter of combustion. Oxygen present in the air also supports combustion. Pure carbon dioxide turns lime water milky. Carbon dioxide present in the air also turns lime water milky.

(ii) The proportions of the constituents of air vary from place to place. Even in the same place, the proportion varies from time to time. In a compound, the proportions of different constituents always remain fixed.

(iii) On distillation of liquefied air, nitrogen distills off first, leaving behind oxygen in the liquid form. This is the characteristic of a mixture, not of a compound.

(iv) No thermal change occurs when the constituents of air (oxygen, nitrogen etc.) are mixed together.

(v) Liquid air does not have a fixed boiling point. This is the characteristic of a mixture, not of a compound.

Answer 2

Explanation:

Air is a mixture of gases. It contains gases like oxygen, hydrogen, nitrogen, etc. It also contains dust particles, microbes, chemicals released from factories, etc. That is why it is not a pure substance and also called mixture

Hope you got the answer