Page 102 - ICSE Chemistry 6

Procedure
• Now carefully lt the glass tumbler.

Observa on: You will see bubbles coming
out of the tumbler as the water goes inside
it.

Conclusion: The bubbles contain air which
shows that air is present everywhere.

Evidence to Confirm that Air is a Mixture

Following are the evidence that give the confi rma on that air is a mixture of gases and not a compound.
• The composi on of air is not constant everywhere. It varies from place to place and me to me.
The air at higher al tudes contains less oxygen as compared to the plains.

During rainy season, the weather is more humid compared to summers as air contains more water
vapour. The amount of impuri es such as sulphur dioxide, carbon dioxide, etc. are more near
industrial areas.
The composi on of a compound is fi xed and does not vary from place to place and me to me.
This confi rms that air is a mixture and not a compound.

• There is no energy change when the cons tuents of air are mixed together. However, energy
change takes place during the forma on of a compound.
• The cons tuents of air retain their individual proper es whereas the proper es of a compound
are totally diff erent from those of its cons tuents.

• Air is not represented by any chemical formula whereas compounds have defi nite formulae.
• The components of air can be separated by simple physical methods whereas it is not possible to
separate the components by physical methods in case of compounds.

USES OF COMPONENTS OF AIR

Air is vital for the survival of living beings. Air consists of diff erent components which are important and
have diff erent uses. Let’s study about these components and their uses.

Oxygen

Oxygen cons tutes about 21 per cent of the air. The presence of oxygen is essen al for survival of living
organisms. All animals and plants need oxygen for respira on.

Oxygen is also present in water in dissolved form which is taken Thirst for Knowledge
up by aqua c animals for respira on.
During respira on animals and
Oxygen supports combus on, i.e., combus on can occur only
plants take in oxygen and give out
in the presence of oxygen. It is due to this reason that when carbon dioxide and water vapour.
something catches fi re, it is advised to wrap it in a woollen

88