Do you know that the air that you breathe is a mixture of elements in proportion? The earth is completely enveloped in a blanket of air, which is referred to as the atmosphere. The chief natural gaseous constituents of air and their percentage composition by volumes are as follows:
| Constituent | % by Volume |
| Nitrogen | 78.1 |
| Oxygen | 20.9 |
| Noble(or rare) gases | 1.0 |
| Carbon(IV) oxide | 0.03 |
| Water Vapour | Variable(0-1.2) |
Nitrogen accounts for about 4/5 of the atmosphere by volume while oxygen occupies the remaining 1/5. Oxygen constitutes about 21% of the volume of air and is the most active component of the air. It supports life. It is responsible for the rusting of iron and burning(combustion) of substances in the air.
There are various experiments that can be used to determine the proportion of oxygen in air and some of them include the burning of phosphorus in air, and the use of an alkaline pyrogallol solution.
Carbon(IV) oxide is about 0.03% by volume of the atmospheric air. The presence of Carbon(IV) oxide is due to the following procedures: combustion of fuels containing carbon, respiration processes in plants and animals, and all decaying processes.
The prescence of Carbon(IV) oxide can be detected by passing air into limewater which is a solution of Calcium hydroxide Ca(OH)2. The limewater turns milky due to the formation of insoluble calcium trioxocarbonate(IV).
Noble gases constitute about 1.0% of atmospheric air and from our articles in the periodic table articles, we clearly stated that inert gases are chemically inactive because they do not have valence electrons in their outermost shells. Helium is used in filling balloons because it is light and does not support combustion while neon and argon lights are used in advertising electrical signs because of the beautiful lights they produce.
Impurities in air include Hydrogen Sulphide H2S, Sulphur Oxide SO2, Carbon(II) Oxide CO, and soot.
Reasons Why Air Is Called A Mixture
The following are reasons why air can be termed as a mixture:
- The composition of air varies from one place to another, depending on the humidity.
- If nitrogen, Oxygen, and Carbon(IV) oxide are mixed together, there is no volume change, no explosion, and no sign of any chemical reaction
- Air can be separated into its main constituents by fractional distillation of liquid air.
- There is no chemical formula for air
Exposure Of Certain Substances To Ordinary Air
When certain substances are exposed to the atmosphere, they either gain or lose weight. Categories of these substances are outlined below.
| Deliquescent Substances | These are compounds that absorb moisture from the atmosphere and form a saturated solution. They gain weight when exposed to the atmosphere. examples include NaOH, and KOH |
| Hygroscopic Substances | These are substances that usually absorb moisture from the atmosphere without forming a solution. Examples include NaCl, Cao, and CuO |
| Efflorescent Substances | These are crystalline compounds which on being exposed usually lose their water of crystallization to the atmosphere. |
| Drying Agents | Deliquescent and hygroscopic compounds are used as drying agents for gases, liquids, and solids since they are capable of absorbing moisture. |
Air Pollution
The term pollution is a phenomenon in which certain substances that are harmful to living things are present, in large excesses in the environment. Such contaminants are called pollutants. The two types of air pollution include natural and artificial pollution. Two major air pollutants are soot and Carbon(II) oxide.