1. Air
Chapter 31 Page 186

3. The Earth’s early atmosphere
Early atmosphere formed by gases given out by volcanoes
Mostly carbon dioxide with little or NO oxygen
Most of the water vapour condensed and formed oceans
Scientists believe that the Earth was formed about 4.5 billion years ago.
Its early atmosphere was probably formed by the gases given out by volcanoes  it is believe that there was intense volcanic activity for the first billion years of the Earth’s existence.
The early atmosphere was probably mostly carbon dioxide , with little or no oxygen.
There were smaller proportions of water vapour, ammonia and methane.
As the Earth cooled down, most of the water vapour condensed and formed oceans.
It is thought that the atmospheres of Mars and Venus today which contain mostly carbon dioxide, are similar to the early atmosphere of the Earth.
Smaller proportions of water vapour, ammonia and methane
Very similar to the atmospheres of Mars and Venus

4. Changes to the early atmosphere
So how did the proportion of carbon dioxide go down and the proportion of oxygen go up?
The proportion of oxygen went up because of photosynthesis by plants.
The proportion of carbon dioxide went down because:
It was locked up in sedimentary rocks, such as limestone, and in fossil fuels.
It was absorbed by plants for photosynthesis
It dissolved in the oceans.

5. What is air made of? Air is a mixture of different gasses Nitrogen N2
Oxygen O2
Noble Gasses Ar
Carbon Dioxide CO2
Water Vapour H2O

6. Changes to today’s atmosphere
Where has this increase in carbon dioxide come from?
Most of the UK’s electricity is produced by power stations that are fuelled by fossil fuels, which contain carbon.
Carbon dioxide is produced from burning fossil fuels, which is being added to the atmosphere faster than it can be removed.
This means that the level of carbon dioxide in the atmosphere is increasing.
Burning fossil fuels!

7. How can we prove air is a mixture?
Its composition varies – in compounds the composition is constant
If air is cooled down to low temperatures the gasses all become liquids at different temperatures – in compounds gasses would change state at the same time
The components of air can be separated individually

8. How can we prove air is a mixture?
When the gasses air mixed together in the right amounts they form air, no heat is given out or taken in so no new compound is made

9. How can we show the amount of oxygen in air?
The candle uses up all of the oxygen in the air until it goes out. The level that the water rises could be used to calculate approx. that 21% of air is made up of oxygen.

10. How can we show that the air contains carbon dioxide?
Carbon Dioxide, turns lime water milky.

11. How can we show that the air contains water vapour?
Turns blue cobalt chloride paper pink

12. Oxygen
Oxygen is prepared in the lab by looking at the breakdown of Hydrogen Peroxide This is however a very slow reaction so we use a substance called a catalyst A Catalyst is a substance that speeds up a chemical reaction without being used up in the reaction

13. Oxygen Chemical equation: 2H2O2 2H2O + O2 MnO2
Hydrogen Peroxide Water + Oxygen
MnO2
Manganese Dioxide

14. Oxygen Properties: 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 is not acidic or basic
5. Oxygen relights a glowing splint – this is the test for oxygen
6. Oxygen is a very reactive element. It combines with other elements to form oxides

15. Oxygen
Acidic – Carbon dioxide C + O2  CO2 Basic – Magnesium Oxide 2Mg + O2 2MgO

16. Oxygen
Uses:
Breathing – our cells need oxygen to release energy from our food
Welding – Cutting and welding requires a very hot flame, this is achieved when acetylene is mixed with oxygen
Burning – Oxygen is needed for the burning of fossil fuels

17. Preparing oxygen
We will look at this next week

18. 03/12/13

19. Preparing Oxygen Today we will
Prepare oxygen using hydrogen peroxide and manganese dioxide
Conduct the tests for oxygen

20. Preperation of Oxygen

21. Oxygen Chemical equation: 2H2O2 2H2O + O2 Word Equation : MnO2
Remember:
Reactants  Products
Oxygen
Chemical equation:
2H2O H2O + O2
Word Equation :
Hydrogen Peroxide Water + Oxygen
MnO2
Manganese Dioxide

22. Testing for Oxygen Relight a glowing splint
Neutral – moist red and blue litmus stay red and blue

23. 10/12/13

24. Today we will… Look at the production of Carbon dioxide
How it is produced
Its properties
Its Uses
We will make some!

25. Carbon Dioxide
Carbon Dioxide can be prepared in the lab by reacting dilute, Hydrochloric acid and marble chips
Calcium carbonate + Hydrochloric acid 
Calcium Chloride + Water + Carbon Dioxide
CaCO3 + 2HCl  CaCl2 + H2O + CO2

26. Properties of Carbon Dioxide
CO2 is a colourless, odourless, tasteless gas
It is an acidic gas – Turns blue litmus paper red
Does not support combustion (burning)
It is denser than air

27. Properties of Carbon Dioxide
5. It turns limewater milky – this is the test for carbon dioxide
Ca(OH)2 + CO2  CaCO3 + H2O
Limewater + Carbon dioxide  Chalk + Water

28. Properties of Carbon Dioxide
6. It dissolves in water to form an acidic solution that turns blue litmus paper red CO2 + H2O  H2CO3 Carbon dioxide + Water  Carbonic Acid

29. Uses of Carbon Dioxide
Photosynthesis – green plants use it to make their food
Fire Extinguishers – puts out fires
Fizzy Drinks – It is dissolved under high pressure in fizzy drinks

30. The Production of CO2 (Pg 105)

31. Procedure
Set up as shown (calcium carbonate is the chemical name for marble chips).
Slowly release the hydrochloric acid into the flask underneath.
Carbon dioxide is collected it the gas jar
Test 1:
Pour a small volume of limewater into the jar and shake – the limewater will turn milky showing that the gas is carbon dioxide.
Test 2:
Add water to a fresh jar of carbon dioxide and test with blue litmus paper: it turns red demonstrating that it is an acid.