Q.7. Describe an experiment to prove that air has oxygen
Answers
Solution:
Experiment - to show oxygen and nitrogen component in air using a bell jar.
Apparatus - a trough, a bell jar, a cork, a crucible and a piece of white phosphorus.
Procedure - A trough is filled with and a bell jar is labelled into 5 equal parts.
A crucible which has white phosphorus is placed on a cork is floating in the water.
The level of water inside the jar and outside the jar are adjusted to one level
The phosphorus is ignited by means of an ignited wire.
Observation - The phosphorus burns in air with oxygen and forms dense white fumes of phosphorus pentoxide.
The level of water inside the bell jar rises by 1/5th.
Conclusion - Oxygen is the active component in air which burns phosphorus and nitrogen is the inactive component of air which is not used in burning.
Aim of experiment: To show that air contains nitrogen and oxygen in the ratio 4:1 by volume.
Procedure: Take a glass container and fix a candle at its center. Put some quantity of water in the container. Place an empty, dry gas jar over it. Mark five marks above water surface on the jar at equal distances shown in the figure given below.
The candle is lightened and is covered with the gas jar. After some time the candle is extinguished and the water level is raised in gas jar. The raised level in water is 1/5 of the volume of air in the gas jar.
This proves that one part of the air of the jar is a gas which supports combustion, i.e., oxygen. Hence, 1/5 by volume is oxygen in air.