Question 12
Describe simple experiments to show the presence of –
(a) oxygen and nitrogen component in air using a bell jar.
(b) carbon dioxide in air using a test tube with outlets containing lime water.
(c) water vapour in air using a glass tumbler and ice.
(a) To study the presence of oxygen and nitrogen component
Apparatus : A trough , bell jar, cork and crucible, a piece of phosphorus.
Procedure :
- The trough is filled with water and a bell jar divided into 5 equal parts, '1 to 5' is placed over it.
- A crucible containing white phosphorus is placed on a cork which is made to float on water.
- The level of water inside and outside are adjusted to one level.
- The phosphorus is then ignited by means of a heated wire.
Observations :
White fumes are seen initially in the bell jar and level of water in the bell jar rises by 1⁄5.
Phosphorus + Oxygen ⟶ Phosphorus pentoxide
Conclusion :
- Oxygen the active component of air [i.e., 1⁄5th of air] is used up in burning.
- Nitrogen the inactive component of air [i.e., 4⁄5th of air] is not used up in burning.
Hence air contains oxygen which supports combustion and nitrogen which does not support combustion.
(b) To study the presence of carbon dioxide in air
Apparatus : A test tube containing lime water with two outlets - A and B.
Procedure : Air is sucked slowly from the outlet B
Observations : The lime water in the test tube turns milky.
Conclusion : Air contains carbon dioxide which turns lime water milky.
(c) To study the presence of water vapor in air
Procedure : A glass tumbler filled with ice cubes is exposed to the air.
Observations : Water droplets are seen on the outer surface of glass tumbler
Conclusion : Air contains water vapour which condenses on the cool outer surface.