BAHRIA COLLEGE ISLAMABAD Class 7 th Unit no

BAHRIA COLLEGE ISLAMABAD Class : - 7 th Unit no: - 9 Unit no: -10 Unit no: -11 Unit no: -12 First term syllabus G. Science

Unit 12 : AIR We are surrounded by air � It supports life to take place such processes photosynthesis , combustion , respiration. � It provide medium for sound to travel. � Our earth is surrounded by thick layer of air called atmosphere � It protects earth from harmful; rays of sun.

AIR HAS MANY USES �Wind is used to move the sail boat. �Air blown into recorder vibrates to produce a nice sound. �Compressed air is used to work pneumatic drill �Air bag is a safety device in car to save life when accident occur.

Composition of Air NAME OF GAS PERCENTAGE % Oxygen 21% Noble gases 1% Nitrogen 78 % Carbon dioxide 0. 03%

Why is air a mixture ? � Component of air can be separated by fractional distillation � Air is first liquefied by cooling and compressing � Liquid air is warm up. � Different gasses boil of from liquid at different temperatures because their boiling points are different.

IDENTIFICATION TEST � To � identify oxygen: If we take a burning match stick in to a test tube of oxygen it will burn more brightly. � To identify carbon dioxide : � When carbon is passed through lime water in a test tube it turns milky. � Ca(OH)2 +CO 2 Caco 3 + H 2 O

PROPERTIES OF GASES IN AIR

REVIEW QUESTIONS

Prepared by: - Ghazala Sehar