Page 103 - ICSE Chemistry 6

blanket. This cuts off the supply of oxygen and hence, stops the Combus on
fi re from spreading further.
A chemical reac on in which heat and
Let’s perform Ac vity 5.2 to observe that oxygen supports light are produced when something
combus on. reacts with oxygen present in the air.

Activity 5.2

Aim: To observe that oxygen supports combus on
Materials required: 3 candles, a 250 mL beaker, a 500 mL beaker, a matchbox

Procedure
• Go to a room and close all doors and windows. Also switch off fans.

• Take three candles, light them and fi x them on a table at some
distance from each other.
• Take a 250 mL and a 500 mL beaker.
• Cover the fi rst candle with the 250 mL beaker and the second candle
with the 500 mL beaker.

• Leave the third candle uncovered.
• Observe the three candles for some me.
Observa on: You will observe that the fi rst candle covered with the 250 mL beaker stops burning fi rst.
Then the second candle covered with the 500 mL beaker ex nguishes. The third candle that was uncovered
con nues to burn.

Conclusion: This happens because the beakers trapped some air (oxygen). The candles used up all the air
present inside the beaker for burning. When whole of the air was used up, the candles stopped burning.
The fi rst candle ex nguished fi rst because the 250 mL beaker trapped lesser air as compared to the
500 mL beaker. The third candle that was uncovered con nued to burn as it had regular supply of air.

Nitrogen

Nitrogen cons tutes about 78 per cent of the air. It does not
Thirst for Knowledge
support combus on. Nitrogen is needed by plants to grow.
Leguminous plants like pea, beans, len ls, soy and groundnuts Leguminous plants can work as
have the ability to convert atmospheric nitrogen into soluble fer lisers and increase the nitrogen
nitrogenous compounds that can be absorbed by plant roots. This content of the soil.
process is called nitrogen fi xa on. Fer lisers containing nitrogen
are added to non-leguminous plants to fulfi l the requirement of nitrogen. Human beings and animals also
need nitrogen to grow. They get their supply of nitrogen by consuming plants and plant products.

Nitrogen is supplied back to the soil when plants and animals die and decay. This balances the amount of
nitrogen in the air that can be used again and again.

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