Composition of air

Introduction to Air

Think of air as a big mixture of gases around us. It is like a fruit salad where different fruits are mixed together, but you can still pick them apart. Air covers the earth like a blanket, and we call this blanket the atmosphere. Even though you cannot see air, it is there, and it is a mixture, not a compound.

Simply put, air is just a collection of different gas molecules floating together in space.

The major components of air

The air we breathe is not just one thing. It contains four main gases in specific amounts. Even if you go to a market in Lagos or a farm in Kano, these percentages stay roughly the same.

1. Nitrogen: This takes up about 78 percent of the air. It is the 'lazy' gas because it does not react easily. It helps to slow down the way things burn.

2. Oxygen: This takes up about 21 percent. This is the one we need to stay alive. It also makes your firewood or gas cooker burn.

3. Noble Gases: These are mostly Argon. They make up about 0.9 percent. They do not react with anything at all.

4. Carbon (IV) Oxide: This is only about 0.03 percent. Even though it is small, plants need it to make food.

These are the silent gases in the air that do not like to join others in chemical reactions.

Other things found in air

Apart from the four main gases, air also contains water vapour. This is why your cold bottle of 'Coke' gets wet on the outside when you bring it out of the fridge. The water in the air touches the cold bottle and turns back to liquid. The amount of water vapour changes depending on if it is rainy season or harmattan.

Air also contains dust and smoke. If you look at a beam of light entering a dark room, you will see tiny particles dancing. Those are dust particles.

Proving air is a mixture

In your WAEC or NECO exams, they often ask why air is a mixture and not a compound. Here are the reasons:

The components can be separated by a physical method like fractional distillation of liquid air.

The gases in air still keep their own properties (Oxygen still supports fire, Carbon (IV) oxide still turns lime water milky).

No heat or light is produced when the gases are mixed together.

The formula of air cannot be written like H_2O because the composition can change slightly depending on the location.

Separating air components

To separate air, we first cool it down until it becomes a liquid. Then we use fractional distillation. Because Nitrogen has a lower boiling point of -196 degrees Celsius and Oxygen has a boiling point of -183 degrees Celsius, Nitrogen boils off first and is collected.