Question

Describe a simple experiment to show that l/5th of air is oxygen.

Answer 1

Aim : To show that l/5th of the air is oxygen.
apparatus required : Glass trough, bell jar, stopper, water, phos-phorus, evaporating dish
PROCEDURE

1. a glass trough is filled with water
2. A dry evaporating dish containing white phosphorus is made to float on the water.
3. This apparatus is covered with a well stoppered bell jar with markings on its side.
4. A glowing iron wire is introduced into the bell jar by opening the stopper
5. The phosphorus is carefully ignited.
6. Re-stopper the apparatus
7. The phosphorus bums with a brilliant flame farming dense white fumes of phosphorus pentoxide.
8. Soon the burning ceases and the water level starts rising.
9. The water occupies approximately l/5th of the original volume, as the fumes dissolve in water.
10. Some phosphorus is left unburnt in the dish. The air left behind in the bell jar does not allow the phosphorus to burn.

INFERENCE : The experiment shows that the volume of air oc-cupied by oxygen is 1 /5th.