Air

1
Air

• Chapter 31

2
Air

• Air is a mixture of gases which forms a blanket
  around the earth.
• Another name for air is the Atmosphere.

3
Composition of Air
The main gases in air are

• Nitrogen 78
• Oxygen 21
• Inert gases and Carbon Dioxide 1

4
Proof that Air is a mixture

• Air is a mixture because
• Its composition varies from place to place.
• The different gases condense as liquids at
  different temperatures. N2 -196o C O2 -183o C
• When the gases are mixed in the right proportions
  the result is air.

5
Experiment To measure the of Oxygen in air

• 1. Set up apparatus as shown in Diagram.
• 2. 100 cm3 of air is passed backward and forward
  over the heated copper.

6
To measure the of Oxygen in air

• Results
• Volume of air before heating 100cm3
• Volume of air after heating 79cm3
• Calculations
• Oxygen
• decrease in volume of air x 100 21 x
  100 21
• initial volume of air
  100
• ConclusionPercentage of Oxygen in Air 21

7
Experiment To show that Carbon dioxide is
present in air.

• 1. Set up apparatus as shown in the diagram.
• 2. Allow air to be drawn through the limewater
  for about half. an hour.
• Result
• The limewater turns milky
• Conclusion
• This shows us that carbon dioxide is present in
  air

8
Experiment To show that water vapour is present
in air.

• 1. Set up apparatus as shown in diagram.
• 2. Test the liquid with the cobalt chloride paper
  and observe the copper sulphate.
• Results
• The liquid turns the white anhydrous copper
  sulphate blue
• The blue cobalt chloride paper turns pink.
• Conclusion
• Water vapour is present in air

9
Oxygen

• Oxygen makes up 21 of the air.
• It is prepared in the Laboratory by the breakdown
  of Hydrogen Peroxide(H2O2) into Oxygen(O2) and
  Water.
• 2H2O2 --gt 2H2O O2
• Manganese Dioxide acts as a catalyst.
• A catalyst is a substance that changes the speed
  of a chemical
• reaction but is not used up in the reaction itself

10
Preparation of Oxygen
1. Set up apparatus as shown in diagram 2. Allow
the Hydrogen peroxide to fall on the Manganese
Dioxide catalyst. 3. Collect the gas given off
11
Properties of Oxygen
Test for Oxygen
Oxygen re-lights a glowing splint
Properties of Oxygen
12
Formation of Oxides

• Oxygen is a reactive element and it combines with
  other elements to form oxides.

Reaction with Carbon C O2 --gt CO2
Carbon Oxygen --gt Carbon Dioxide
Carbon forms an Acidic Oxide
13

• Reaction of Oxygen with Magnesium

Magnesium burns in Oxygen to form Magnesium
Oxide. 2Mg O2 --gt 2MgO Magnesium forms
a basic Oxide
14
Uses of Oxygen

• 1. Breathing
• 2 Welding
• 3 .Burning
• 4. Medicine
• 5. Manufacture of Steel
• 6. Space-rockets

15
Carbon Dioxide

• Carbon dioxide makes up less than 1 of the air
  but is a very important gas.
• It is needed by plants for photosynthesis.
• Without Carbon Dioxide plants would not grow.
  Without plants, animals would not survive

16
Preparation of Carbon Dioxide
2HCl CaCO3 --gt CaCl 2 H2O CO2

• Carbon Dioxide is prepared in
• the lab by the reaction between
• Hydrochloric acid(HCl) and
• marble chips(CaCO3)

17
Properties of Carbon Dioxide
Does not support combustion
Heavier Than Air
18
Test For CO2

• Carbon Dioxide turns Limewater Milky.
• Limewater Carbon Dioxide --gt Chalk
  Water
• Ca(OH)2 CO2 --gt
  CaCO3 H2O

19
Carbon Dioxide does not support combustion
20
Uses of Carbon Dioxide

• Photosynthesis
• Fizzy Drinks
• Fire Extinguishers
• Refrigeration
• Stage Shows(Dry Ice)