The layer of air that surrounds the earth is called the atmosphere.
	Air is a mixture of gases.
	Air contains: 78% Nitrogen (N2), 21% Oxygen (O2), 1% Argon (Ar), 0.03% Carbon dioxide (CO2) and water vapour.

 

Properties of Water

Test for Water	Result for Water
Melting Point	0°c
Boiling Point	100°c
Density	1 g/cm3
Add blue cobalt chloride paper	Pink Colour
Add anhydrous copper sulphate	Bright blue colour

 

Oxygen

Physical Properties	Chemical Properties
A colourless gas	Does not burn
Has no smell	Supports Combustion (Relights a glowing splint)
Denser than air	Doesn’t alter litmus, so it is neutral
Slightly soluble in water	Reacts with Carbon to form CO2

 

	Oxygen reacts with non-metals to form oxides, which turn blue litmus red. (They are acids)***
	Oxygen reacts with metals to form oxides, which turn red litmus blue. (They are bases)***
	Test for oxygen: Oxygen relights a glowing splint (a splint of wood that was burning and has just been extinguished).

 

Def: A catalyst is a substance that speeds up a chemical reaction but is not used up in the reaction.

 

Def: An oxide is a compound of oxygen and one other element.

 

·        The oxides of non-metallic substances like carbon are usually acids because they turn blue litmus red.