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Question
Describe a simple experiment to show that l/5th of air is oxygen.
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Solution
Aim : To show that l/5th of the air is oxygen.
apparatus required : Glass trough, bell jar, stopper, water, phos-phorus, evaporating dish
PROCEDURE
- a glass trough is filled with water
- A dry evaporating dish containing white phosphorus is made to float on the water.
- This apparatus is covered with a well stoppered bell jar with markings on its side.
- A glowing iron wire is introduced into the bell jar by opening the stopper
- The phosphorus is carefully ignited.
- Re-stopper the apparatus
- The phosphorus bums with a brilliant flame farming dense white fumes of phosphorus pentoxide.
- Soon the burning ceases and the water level starts rising.
- The water occupies approximately l/5th of the original volume, as the fumes dissolve in water.
- 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.
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