Page 2 - 3-Lesson Notes-Composition of air, Nitrogen, oxygen and Carbon dioxide

❖ It is also used in the preservation of packed food.

Oxygen

❖ Air contains 21% (one fifth) of oxygen. It supports life on this earth.
❖ All living organisms need oxygen for respiration. Aquatic animals take oxygen
dissolved in water. Even animals live in soil, use the air trapped between the soil
particles.
❖ During respiration, we breathe in oxygen and give out carbon dioxide. Oxygen burns
food and releases energy to perform different works.
❖ Oxygen is essential for the combustion of fuel.
❖ With the increase in altitude, the atmosphere gets thinner and the supply of oxygen is
reduced therefore, while climbing high mountains, mountaineers carry oxygen
cylinder.
❖ Human beings cannot breathe inside water. Therefore deep-sea divers carry an
oxygen cylinder with them.

Activity: -
To prove air is needed for burning.

Materials required- a candle, a glass, matchbox.

Procedure- Light the candle with a match stick.
Cover the burning candle with the glass.

Observation- The candle extinguishes after sometime.

Inference-candle extinguishes due to the lack of oxygen.
Oxygen is needed for burning or combustion.

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