SS2 Chemistry Lesson Note on Air

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TOPIC: AIR

CONTENTS:

1. CONSTITUENTS OF AIR
2. PROPERTIES OF AIR
3. AIR POLLUTION
4. 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

1. 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.
2. 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.
3. Carbon (iv) oxide air: The presence of carbon (iv) oxide in air can be proved by the passage of air through aqueous solution of calcium hydroxide (lime water) or KOH. The percentage of carbon (iv) oxide in air is balanced and maintained by the process of respiration and photosynthesis
4. Oxygen in air: oxygen is the most active component of air. It supports life. The process of burning a substance in air is called combustion. Its major reactions include corrosion (rusting), respiration and combustion.

Corrosion: This is the change on metallic surface that is observed after being exposed to air for few days. The corrosion of iron is commonly known as rusting. This can be prevented by (a) Applying grease (b) painting exposed surface (c) coating with metal e.g. chromium

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