Is the atmosphere an essential element for the existence of life on Earth?
A layer of gases, called the atmosphere, surrounds our earth. It is commonly referred to as air.
As fish live in water for survival, all living beings need breathable air in the atmosphere for survival.
Now, let us look at various components of air. Air consists of active and inactive components. Mayow proposed this in the year 1674.
After him, Lavoisier, in the year 1789, further proved and named an active component as oxygen, and an inactive component as nitrogen.
These two gases are the major components of the atmosphere.
Around 80% of the atmosphere is nitrogen and 20% is oxygen, by volume.
Did you know that the air we inhale while breathing is actually a mixture of many gases?
The atmosphere is composed of a mixture of gases such as nitrogen, oxygen, carbon dioxide, water vapour, ozone, and noble gases like helium, neon, argon, krypton, and xenon. It also has particles of dust and carbon, carbon monoxide, nitrogen dioxide, sulphur dioxide, and chlorofluorocarbons (CFCs).
Let us now conduct a simple experiment to see the presence of oxygen and nitrogen in air.
Let us take a test tube eight centimetres long, and place a strip of graph paper, five centimetres long, along its side. Now, place a pea-sized piece of phosphorous inside the test tube, and then fix a cotton wool plug over it. Invert the test tube in a beaker containing water.
You can now observe that the level of water inside and outside the test tube is at the zero mark.
Leave the test tube upright undisturbed for one hour. Now, check the level of water inside the test tube again. Do you observe any change? You will observe that the water level has increased by one centimetre. Do you know why?
This is because of the slow reaction of oxygen with the phosphorus in the test tube.
Oxygen reacts with phosphorus to give phosphorus pentoxide, which then dissolves in water and forms phosphoric acid. Due to this complete reaction between oxygen and phosphorus, the oxygen is completely removed from the test tube. This decreases the pressure of air inside the test tube. To balance the loss in pressure, water from the beaker is pulled into the test tube. You will observe that water occupies only one centimetre of the five centimetres of air that was in the test tube. The experiment proves that air contains one part of oxygen and four parts of nitrogen.
Here is another experiment that proves the presence of carbon dioxide in air.
Fill about 4 millilitres of limewater in a test tube. Close it with a two-holed rubber stopper.
Fix a delivery tube through each hole. Immerse one end of delivery tube A in limewater and the other end of delivery tube B should remain above the surface.
Suck air from delivery tube B for few seconds.
Now, the pressure inside the test tube decreases, resulting in air from outside entering the test tube through delivery tube A. You will notice that the limewater turns milky. This is because of the formation of insoluble calcium carbonate. This proves that air contains carbon dioxide.
Did you know that most substances while burning in air react with oxygen only to form their respective oxides? When coke burns in air, it forms carbon dioxide.
Now, take a look at an experiment to know the presence of water vapour in air.
For this experiment, we need a clean and dry glass tumbler.
Ensure that there is no water on it.
Add some crushed ice to the tumbler.
You will observe tiny droplets of water appear on the outer surface of the tumbler within a short time.
Do you have any idea as to why the water droplets formed?
This is that due to the change in the physical state of matter from gaseous phase to liquid phase, called condensation.
Thus, water vapour in the air changed into liquid and formed as tiny water droplets on the surface of the glass tumbler.
This proves that air contains water vapour.