1. Chemistry of the Atmosphere

2. The composition of air
Around 78% of the air is nitrogen.
About 21% is oxygen.
The remaining 1% is mostly argon (0.93%), with carbon dioxide (.04%) and varying amounts of water vapour.

3. Separating gases Activity
Here are the boiling points of the three main gases in air.
Nitrogen: - 196ºC
Oxygen : ºC
Argon: ºC
When air is distilled:
Which gas will boil first?
Which gas will there be most of?
Which gas will there be least of?
Nitrogen
Nitrogen
Argon

4. Separating the gases in air – Liquidation and Fractional distillation

5. Uses of oxygen
1. Oxygen can be stored in cylinders to help people to breathe :

6. Uses of oxygen
2. Oxygen is used in acetylene torches to burning metals at very high temperatures – WELDING!

7. Nitrogen gas Nitrogen exists in the atmosphere as N2
It is very unreactive (inert) because the nitrogen atoms are bonded together by a triple bond, which is very hard to break up

8. Uses of pure nitrogen gas
Used to keep foods fresh
Used to flush out dangerous vapours from oil tankers
Based on inertness

9. Uses of liquid nitrogen
Used as a coolant:
To store sperm cells in cold conditions
To kill damaged skin cells (like warts) by freezing them

10. Nitrogen fixation Nitrogen is needed by plants to make proteins.
However, nitrogen itself is too un-reactive for plants to be able to use.

11. Natural nitrogen fixation
Nitrogen fixation = converting nitrogen gas into the nitrates that plants can use
Thunderstorms
N2 + O NO ( lightning causes the reaction)
NO changes to NO2 when cooled
Reacts with rainwater to make HNO3 (nitric acid)
Nitric acid falls to the earth
and will produce nitrates in the soil

12. Natural nitrogen fixation
2) bacteria which live in the roots of plants also convert nitrogen gas to nitrates .

13. Nitrogen cycle Ammonia Death Death Role of animals Role of plants
Role of nitrogen fixing bacteria – convert nitrogen gas to nitrates( no3) live in the soil and in the roots of legumes such as peas, beans and lentils
Role of nitrifying bacteria- convert ammonia to nitrates by decomposing the humus and waste material in the soil.
Role of denitrifying bacteria- bacteria which conbert nitrates into nitrogen gas.
Death
Ammonia

14. The Nitrogen Cycle

15. The Nitrogen Cycle
A drag and drop activity

16. Carbon MONOXIDE C + ½ O2 CO ( incomplete combustion)
Carbon monoxide in cigarette smoke and vehicle exhaust fumes.

17. About carbon monoxide
Unlike carbon dioxide, carbon monoxide is neutral.
CO is a deadly poison which prevents the uptake of oxygen by haemoglobin the blood

18. Carbon DIOXIDE
C + O2 CO2 ( complete combustion)

19. Carbon dioxide
Is an acidic gas
Used in fizzy drinks

20. Making carbon dioxide
When yeast ferment glucose they make alcohol and carbon dioxide.
C6H12O6 C2H5OH + 2CO2

21. Carbon Dioxide in the air
Carbon cycle
Carbon Dioxide in the air
Burning of Fossil Fuels
Photosynthesis
Respiration
Feeding
Emphasise the role of the organisms in the cycle:
Plants
Animals
Microorganism
Why do you think the co2 levels are going up in the world?Global warming!more animals, less photosynthesis
Seasonal fluctuations normal (do to with rate of photosynthesis)
Death and Decay
Death and Decay
Death and Decay
Formation of Fossil Fuels
bacteria & fungi decompose

24. The greenhouse effect

25. The greenhouse effect
The greenhouse effect is when certain gases in the atmosphere trap some of the heat given off from Earth.
Without the atmosphere and the greenhouse effect, Earth would be too cold for life to exist!

27. Carbon dioxide and temperature
Over millions of years the carbon cycle has maintained a constant, low percentage (approx. 0.03%) of carbon dioxide in the atmosphere.
In 1860, the CO2 level was about 289 ppm (parts per million).
Here is a table showing the CO2 levels over a recent 10 year period.
What percentage change is this and does it matter?

28. Greenhouse effect Which label goes with each picture? 200ppm CO2

29. Gases involved in Global warming
Carbon dioxide is a greenhouse gas (factor of 1) involved the warming of the Earth by the greenhouse effect.
Methane is another greenhouse gas (factor 30) – produced by marshs, rubbish dumps and in the digestive tracts of animals.
CFCs (factor 25,000) and water (factor 0.1) are also greenhouse gases!
CFCS – low abundence
H20 – massive abundence

30. Increase in greenhouse gases
An increase in the amount of greenhouse gases could increase the amount of heat trapped in the atmosphere making the Earth warmer and leading to global warming.
Which of the greenshouse gases are increasing, and what is causing this increase?

31. Effects of global warming
temperature – some areas may be warmer, others colder;
Changes in prevailing winds
coastal flooding – sea levels could rise as ocean’s get warmer;
rainfall – some areas may be wetter and others drier;

32. The ozone layer

33. The ozone layer
The ozone layer is an invisible layer of ozone gas O3 that is found in the stratosphere of the earth.

34. How ozone is formed
decomposition of oxygen molecule into oxygen radicals by high-energy ultraviolet (uv) light
O O. + O.
2. reaction of oxygen radical with oxygen molecule forming ozone
O2 + O. O3

35. How the ozone layer works
The ozone layer acts like a sunscreen by absorbing most of the UV radiation that comes from the sun

36. The photo dissociation reaction of ozone
Uv light in the stratosphere breaks down ozone as follows:
O3 + uv O2 + O.
But ozone is not lost as the following reaction also happens:
O2 + O. O3
So overall there is a balance and ozone levels should stay constant

37. They are prepared by the chlorination of alkanes
CFCs
Chloroflourocarbons (CFCs) are used as refrigerants and in fire extinguishers.
Examples – CCl2F2, CCl3F
They are prepared by the chlorination of alkanes
INERT, NON FLAMMABLE, NON CORROSIVE, NON TOXIC

38. CFCs and the ozone layer
CFCs destroy ozone molecules and so damage the ozone layer.
They are stable and soluble in water so they stay in the atmosphere for a long time

39. How CFCs cause ozone depletion
The CFCs react once in the presence of uv light
CCl3F + uv CCl2F. + Cl.
2. The chlorine free radicals attack ozone
Cl. + O3 ClO. + O2
3. These free radicals react with Oxygen free radicals to regenerate more Cl free radicals so the cycle continues
ClO. + O. O2 + Cl .

40. Damage to the ozone layer means that more ultraviolet radiation reaches the earths surface.
Effects:
Causes skin cancer
Causes damage to plants

41. HCFCs and HFCs These chemicals are now being used instead of CFCs.
Examples C2H3Cl2F and C2H2F4
The C-H bond is generally broken down before they reach the stratosphere so less chorine free radicals are emitted.
They are still greenhouse gases :(

42. Do you know? What the ozone is made from and where it is found
Beneficial effect of the ozone layer.
Photodissociation of ozone (equation required).
Formation of ozone in the stratosphere (equation required).
What CFCs are and what they are prepared from
Chlorofluorocarbons and the effect on the ozone layer.( equations required)
Residence times of CFCs.
Effects of damage to the ozone layer.
Replacements for CFCs : HFCs and HCFCs??

43. Acid rain

44. Normal rainwater has a pH of about 5
Normal rainwater has a pH of about 5.5 which means it is naturally slightly acidic.

45. Acid rain Rainwater with a lower pH than normal is called acid rain.
The burning of fossil fuels in power stations and in cars
forms sulfur oxides and nitrogen oxides .
These gases dissolve in rainwater to make acids, which form acid rain.

46. Causes of acid rain - HL 1. Formation of Nitrogen oxides
N2 + O NO ( this reaction can only happen if enough energy is provided – lightening storms and combustion reactions)
NO + ½ O2 NO2
This dissolves in water to form HNO2 and HNO3, which are acids and cause acid rain

47. Causes of acid rain - HL 2. Formation of sulfur oxides
SO2 dissolves in water to form H2SO3 (SULPHUROUS ACID)
SO2 can also be oxidised to SO3 ( sulfur trixoide) which dissolves in rain water to make H2SO4 sulfuric acid
Both H2SO3 and H2SO4 cause acid rain

48. Acid rain animation

49. What can be done to reduce acid rain and its effects?
Effects of acid rain
Chemical weathering of buildings.
Rivers, lakes and streams become more acidic so that animals and plants cannot live in them.
Acid rain also damages trees
What can be done to reduce acid rain and its effects?

50. Reducing acid rain
Sulfur dioxide can be removed from the gases that are released to the atmosphere by using a scrubber made of limestone.
Nitrogen oxides a car’s exhaust system can be fitted with a catalytic converter which turns harmful gases into harmless gases.