Question
How do you establish that air is a mixture and not a pure substance?
Solution
Air is a homogeneous mixture of several gases.
mostly of nitrogen (~78%) and oxygen(~20%). There are other gases as well; argon slightly less than 1%, and of course, carbon dioxide, (~.04%). Therefore it can be established as follows:
(i) The amounts of gases present in air at different places varies only marginally.
(ii) No definite formula can be assigned to air.
(iii) The different gases present in air are not separable by a physical process : fractional distillation of liquid air.
(iv) The properties of air are the properties of its constituents. Air supports combustion because of oxygen present in it. Air turns lime water milky due to the presence of carbon dioxide in it.
