1. Air
Chapter 31

2. Air The air we breath is a mixture of gases. Air contains: Gas %
Nitrogen (N2) 78
Oxygen (O2) 21
Noble gases (Ar)
<1
Carbon Dioxide (CO2)
0.03
Water Vapour (H2O)
0 - 4

3. Proof Air is a Mixture Its composition varies.
The components of air can be separated individually.
No heat of reaction when the gases mixed form air.

4. To Show % Oxygen in Air

5. To show air contains Water Vapour and Carbon Dioxide
Test for water:
Water turns blue cobalt chloride paper pink.
Test for carbon dioxide:
Carbon Dioxide turns limewater milky.

6. To show air contains Water Vapour and Carbon Dioxide

7. Preparation of Oxygen 2H2O2 MnO2 2H2O + O2
Oxygen is prepared in the lab by the breakdown of hydrogen peroxide H2O2.
The decomposition of H2O2 is slow so a catalyst is used.
Hydrogen Peroxide Manganese Dioxide Water + Oxygen
2H2O2 MnO2 2H2O + O2

8. A Catalyst
A Catalyst is a substance that speeds up or slows down a chemical reaction without being used in the reaction itself.
E.g. Manganese Dioxide MnO2

9. Preparation of Oxygen

10. Preparation of Oxygen

11. Properties of Oxygen Oxygen is a colourless, odourless, tasteless gas.
Oxygen is slightly heavier than air.
Oxygen is slightly soluble in water.
Oxygen is a neutral gas. It has no effect on moist litmus paper.

12. Test for Oxygen
Oxygen relights a glowing splint.

13. Oxygen Oxygen is a very reactive element.
Oxygen reacts with other elements to form oxides.
Magnesium Oxide turns moist red litmus paper blue.

14. Uses of Oxygen Breathing – Oxygen is needed for respiration.
(Respiration is the release of energy from our food).
Burning – Oxygen is needed for things to burn.
Welding – Welding requires a very hot flame, oxygen gas is used

15. Carbon Dioxide
Carbon Dioxide is prepared by reacting dilute hydrochloric acid (HCl) and marble chips. (CaCO3)

16. Preparation of Carbon Dioxide

17. Properties of Carbon Dioxide
Carbon Dioxide is a colourless, odourless, tasteless gas.
Carbon dioxide is an acidic gas. (Turns moist blue litmus paper red)
Carbon Dioxide does not support combustion.
Carbon Dioxide is denser than air.

18. Test for Carbon Dioxide
Carbon dioxide turns limewater milky.
Equation:

19. Carbon Dioxide and Water
Carbon Dioxide dissolves in water to form an acidic solution.
Equation

20. Uses of Carbon Dioxide
Fizzy Drinks: Carbon dioxide is dissolved in fizzy drinks to make the bubbles.
Fire extinguishers: Carbon dioxide puts out fires, therefore it is used in fire extinguishers.
Photosynthesis: Green plants use carbon dioxide and energy form the sun to make their own food.