presence of
(b) nitrogen in the air
(c) water vapour in the air
(d) oxygen and water vapour in the air
used during the process of:
(a) rusting
(b) combustion
(c) photosynthesis
(d) respiration
3. A few drops of clear limewater are poured
in a flat dish and exposed to air for half an
hour. The drops of limewater turn milky due
to the presence of:
(a) nitrogen
(b) sulphur dioxide
(c) carbon dioxide
(d) water vapour
4. The process which generates heat energy
in living beings is called :
(a) combustion (b) respiration
(c) photosynthesis (d) decomposition
rick the most appropriate answer
1. Rusting of iron takes place due to the
(a) oxygen in the air
2. Carbon dioxide produced by living beings is
Answers
Explanation:
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.
Carbon dioxide in air using a test tube with outlets containing lime water
Apparatus - a test tube, lime water, two outlets of tube
Procedure - Lime water is added to test tube with two outlets attached to it.
Air is sucked slowly from one outlet.
Observation - The lime water in the test tube turns milky
Conclusion - Air which is sucked contains carbon dioxide which turns lime water milky.
Water vapour in air using a glass tumbler and ice
Apparatus - A clean dry beaker, cube of ice
Procedure - Ice is placed in a clean dry beaker and kept aside.
Observation - Water droplets appear on the outer surface of the beaker, and it can be proved that it is water vapour by using a dry cobalt chloride paper which turns pink in the presence of water.
Conclusion - Water vapour condenses on the cooler surface of the beaker, which proves air contains water vapour.