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WEEK 9
TOPIC: AIR
CONTENTS:
- Constituents of air
- Properties of air
- Air pollution
- Flame
PERIOD 1: CONSTITUENTS OF AIR
Air is a mixture of gases, composed mainly of nitrogen and oxygen with small amounts of Carbon (iv) oxide, noble gases and water vapour. The constituents of air can be separated easily by physical methods. Nitrogen accounts for about 4/5 of the atmosphere by volume, while oxygen occupies the remaining 1/5
Percentage composition
The chief natural constituents of air and their percentage composition by volume are as follow:
| CONSTITUENT | % BY VOLUME | IMPORTANCE AND USES |
| Nitrogen | 78.09 | Acts as important diluent of air to slow down combustion and corrosion |
| Oxygen | 20.95 | For cellular respiration and burning |
| Noble (or rare gas) | 0.93 | Argon is used to in gas-filled electric lamps because it helps to prevent oxidation in lamp filament.
A mixture Krypton and xenon is used in photographer’s flash tube to take high speed pictures Helium is used to fill balloons Radon is used for treating cancer Mixture of helium, neon and argon is used in advertisement signs. |
| Carbon (iv) oxide | 0.03 | For photosynthesis |
| Water vapour | Variable (0-1.2) | |
| Other gases | 0.003 |
PERIOD 3: PROPERTIES OF AIR
- Water vapour in air: The presence of water vapour or moisture in the atmosphere is due to the evaporation of water from the oceans, rivers, lakes, sea and water reservoirs. The amount present in air varies with temperature, the prevailing weather and the position of the place.
- Noble gases in air: Argon is the most abundant of the bobble gases in the air, then neon. Noble gases are generally in reactive. They are used to produce colourful light for advertisement.
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