Question

Q.7. Describe an experiment to prove that air has oxygen.​

Answer 1

Answer:

Oxygen is important gas found in air. It constitutes one fifth of the air by volume. All the living things use it during the process of respiration. Oxygen also helps in the process of burning. We can prove that air contains oxygen by the following activity:

Activity: To prove that air contains oxygen

Materials required:

• a trough, a bell jar with a cork, water, a small porcelain basin, phosphorus and match box.

Procedure:

1. Take some phosphorus in a porcelain basin.
2. Place the basin floating on the water in a trough.
3. Cover it with a bell jar.
4. Note the water level in the bell jar.
5. Burn the phosphorus carefully and close the bell jar immediately by using a cork as shown in the figure.
6. Now observe the water level in the bell jar.

Observation:

It will be found that while burning the phosphorus, the water level in the bell jar falls down and immediately the water rises up.

Conclusion:

While burning the air inside the bell-jar expands due to the heat and pushes the water down. Also the phosphorus combines with the oxygen of the air present inside the bell jar forming phosphorus pentoxide, which is absorbed by water. When the apparatus cools, the air occupies less space which makes the water level rise in the bell jar. It proves that air contains oxygen.