Question

How will you justify that clean air is a mixture and not a compound?

Answer 1

Clean air is considered as a mixture and not a compound because:

• The components of air i.e., different gases like Oxygen $\left({\mathrm{O}}_2\right)$, Nitrogen $\left({\mathrm{N}}_2\right)$, Argon $\left(\mathrm{Ar}\right)$ etc. are combined only physically. They are not chemically combined by any chemical bonds between the gases.
• Air has a variable composition i.e., air does not consists of the same components at different places. Some places have more amounts of a particular gas than others and vice-versa.
• The properties of air are the properties of the gases that are present in the air. In other words, like a mixture the properties of the components are retained in air. This can be proved by the fact that air supports combustion which is a property of Oxygen. This is because the properties of air are the properties of its constituents. If the air was a compound, the properties of air would have been different from the properties of the gases.
• Like a mixture, the components of air can be separated by using physical methods of separation like fractional distillation. A compound can not be separated into its constituents using the methods of physical separation.
• Air does not have a fixed boiling point. This is because it is a mixture of gases. So air boils over a range of $-186°\mathrm{C}\mathrm{to}-196°\mathrm{C}$ because this range covers the temperature values at which the gases present in air boil.

Mixture: When two or more substances (elements or compounds or an element and compound) are mixed in any proportion.

• The components of a mixture can be separated by physical methods of separation.
• Example: A mixture of Sand and Iron $\left(\mathrm{Fe}\right)$ can be separated by using a magnet (physical process) where Iron gets attracted to the magnet leaving behind the sand.

Compound: A compound is a pure substance in which elements combine chemically in a fixed composition to give a compound.

• They can be broken down into elements that make up the compound by using chemical or electrochemical methods.
• The properties of the compound are entirely different from the elements from which it is formed.
• Example: Water $\left({\mathrm{H}}_2\mathrm{O}\right)$, Common salt i.e.; Sodium chloride $\left(\mathrm{NaCl}\right)$