THE ATMOSPHERE: a Vital Resource

1. THE ATMOSPHERE: a Vital Resource essential for life absorbs radiation stabilises the climate

2. The atmosphere is essential for life • all living things exist in the biosphere(the top few meters of the earth’s crust, the oceans & the atmosphere) • the atmosphere contains oxygen and carbon dioxide which are essential for life Respiration in plants & animals: C6H12O6 + 02 CO2 + H2O + energy Photosynthesis in plants: CO2 + H2O  C6H12O6 + 02

3. Atmosphere protects earth from damaging Solar Radiation • Two ways: • OZONE LAYER:UV rays are absorbed in the formation of ozone in the stratosphere • THERMOSPHERE: X-rays interact with oxygen and nitrogen gases in the thermosphere causing high temperatures

4. how does ozone form? UV radiation O2 (g)  O(g) + O(g) O(g) + O2(g) + M(g)  O3(g) + M* ~ M represent a third molecule which is usually N2. It absorbs heat energy from the UV rays to form M* ~

5. The Atmosphere stabilises the earth’s climate • The Greenhouse Effect causes the earth’s climate to remain stable. • Caused by: - UV rays heat earth - earth emits infra red radiation back to space. Because infra red radiation is of a larger wavelength than UV radiation it is absorbed by CO2, water vapour and methane in the stratosphere, thereby trapping heat in the atmosphere

6. The Greenhouse effect

7. How did earth and its atmosphere form? • EARTH: cloud of gas + dust  molten ball of rock ATMOSPHERE:contained gases from volcanoes; methane, ammonia, water vapour and CO2 • water vapour oceans • oxygen accumulated via photosynthesis & the breakdown of water vapour • UV rays were absorbed in the formation of ozone allowing life to evolve

8. GASES IN THE ATMOSPHERE

9. OZONE :Depletion of the ozone layer • ozone exists as a 10 – 30 km band in the stratosphere at a concn of 10 ppm • ozone depleted by gases produced by human activities eg. CFCs (chloroflurocarbons); CCl3F (g) • Stratosphere: CCl3F(g)  CCl2F(g) + Cl(g) Cl(g) + O3(g)  ClO(g) + O2(g) ClO(g) + O(g)  O2(g) + Cl(g)

10. OZONE: a useful material • STERILISATION- used to destory viruses and bacteria- produced by passing an electrical discharge through O2 molecules to form oxygen atoms O + O2  O3- commercial production of ozone is expensive and occurs in an “ozoniser”

11. OZONE: a pollutant • POLLUTANT in the Trophosphere- at concns of 0.3mg/g irritates the eye- at concns > 0.3mg/g causes respiratory problems- causes rubber and textiles to deteriorate by attacking the double bonds carbon to carbon bonds of unsaturated compounds

12. OXYGEN and industry • manufacture of steel • manufacture of chemicals • medical uses • sewage treatment • combustion of fossil fuels

13. OXYGEN: commercial production • Fractional distillation of liquid air • Three main steps: • Air is filtered: dust, water vapour and carbon dioxide are removed • Air is compressed and cooled • Air is expanded and turned to liquid - oxygen is then separated according to its boiling point

14. Commercial Production of O2

15. Laboratory preparation of O2

16. Lab preparation of O2 Cont. • Prepared from the decomposition of H2O2(aq), using manganese dioxide (MnO2) as a catalyst. • A catalyst is a substance that can increase the rate of a chemical reaction without being used up in the reaction. • Equation for this reaction is : 2 H2O2(aq)  2H2O(l) + O2(g) The oxygen is collected by the displacement of water.

17. Properties of oxygen If you conduct tests on a sample of O2 you will notice: • Is a colourless, odourless gas • Slightly soluble in water. 1L of water will dissolve 0.03L of O2 at 20°C and 1 atm pressure. • Supports combustion. • Reacts with most metals and non metals. Eg in steel making oxygen removes impurities such as carbon and sulphur: C(s) + O2(g)  CO2(g) S(s) + O2(g)  SO2(g)

18. Carbon Dioxide • Like ozone is regarded as a pollutant in certain circumstances. Carbon dioxide is essential to life but is detrimental to the environment when its concentration is too high. • It is a pollutant when its production is out of balance with its consumption.

19. Carbon Dioxide and Life • CO2 occupies about 0.035% of the total volume of the atmosphere. • This concentration is sufficient to sustain life. • The total amount of CO2 the oceans, lakes and rivers is about 20 times that in the air. This CO2 supports photosynthesis of aquatic plants, which in turn supports aquatic animals. • Photosynthesis is the process in which green plants convert CO2 and H2O to glucose and O2. It occurs in the presence of chlorophyll, a green plant pigment, and sunlight. Summarised by:

20. Photosynthesis Cont. The glucose then undergoes condensation polymerisation to form starches and cellulose according to: CO2 is returned to the atmosphere as a by-product of respiration. It is also released into the atmosphere as part of the decay processes occurring after an organism dies.

21. Carbon dioxide and Industry CO2 has a number of uses in everyday life: • Used to make carbonated drinks. Dissolved in the drink at high pressure. Comes out of solution as bubbles when opened. • Solid CO2 (dry ice) used as a refrigerant. Sublimes at -78°C. There is no liquid state. Makes it more convenient to use than ordinary ice in many situations. Doesn’t wet the items being cooled. • Used in fire extinguishers. Denser than air so blankets the flame.

22. Cont. • Fruit and grains such as wheat are sometimes stored in an atmosphere of CO2. Organisms that damage the grain can’t live in this environment. Therefore CO2 must be produced in commercial quantities to meet these needs.

23. glucose ethanol Calcium oxide (quick lime) Calcium carbonate Commercial production of CO2 In industry, CO2 can be obtained as a by-product of the fermentation of sugars to alcohol. CO2 can also be obtained by hating CaCO3 in the form of limestone in a lime kiln:

24. Laboratory preparation of CO2 • Usually prepared in the lab by the reaction of dilute HCl and calcium carbonate in the form of marble chips. • Collected over water. • The diagram shows the apparatus used to make CO2 It is called the Kipp’s apparatus. • Equation below for reaction

25. Properties of CO2 • Colourless and odourless gas • Will not support combustion, unless fire is very hot. Mg is one of the few substances that will continue to burn in CO2. • Denser than air. Accounts for the blanketing effect it has on fire. • Sublimes at -78°C No liquid state. • Slightly soluble in water- 1.5grams per 1L of water.

26. Solutions of CO2 and water are slightly acidic. Most remains as CO2(aq) but small amount reacts with water to form carbonic acid (H2CO3). It is therefore classified as an acidic oxide. It will react with bases to form salts, many of which are insoluble. Carbonic acid is a weak acid and so ionises slightly according to the equation:

27. Test for carbon dioxide If you blow through a straw into a test tube of lime water (calcium hydroxide), a white precipitate. This precipitate is calcium carbonate: This test is often used to identify CO2. If you continue to pass CO2 into the test-tube, the precipitate dissolves to give a colourless solution. Soluble calcium hydrogen carbonate has been formed:

28. This solution is not stable to heat; calcium hydrogen carbonate cannot be isolated as a solid.

29. The Carbon - Oxygen Cycle

30. The Carbon – Oxygen Cycle Cont • CO2 is consumed during photosynthesis in plants • Is produced during the respiration of plants and animals. • O2 is consumed during respiration and produced by photosynthesis. • Cycling of both gases is quite rapid. • CO2 is returned to the atmosphere when an organism dies. This cycling is much slower. • It is the imbalance in this cycle that could lead to problems with the greenhouse effect.

31. Carbon Monoxide CO • Forms a very small percentage of the atmosphere. • Produced naturally in small quantities from the activities of marine organisms, forest fires and volcanoes. • It is produced in sufficient quantities in industrial areas for it to be regarded as a serious air pollutant. • Major sources of CO in cities is from the incomplete combustion of fossil fuels. • Car engines - Power stations • Foundries - Steel mills

32. CO produced in the atmosphere is eventually oxidised to CO2 • Is a colourless and odourless gas. • It poses a health risk in humans because it combines with the haemoglobin in the blood better than O2 , to form carboxyhaemoglobin. This means that if people breath in air containing CO, there is no O2 in their system for their cells. This is seen as a shortness of breath, dizziness and they have a ruddy pink complexion.

33. CO cont. • If untreated, people will lose consciousness and may die from oxygen starvation.

34. Nitrogen • Like O2 and CO2 plays a part in sustaining life in the biosphere. • It is widely used in industry. • It is a diatomic molecule, with the formula N2. • It makes up about 80% of the molecules in the air.

35. Is one of the least reactive molecules in the air, because of its strong triple bond. • Plants require a continual supply of nitrogen, but are unable to use N2, they have to rely on bacteria to convert gaseous N2 into useful NO3- and NH4+ ions. • These bacteria are called “nitrogen-fixing” bacteria, and are found in the nodules on the roots of plants, such as peas, beans, clover and lucerne.

36. Nitrogen is circulated through the biosphere by various chemical and biological processes. This process is called the nitrogen cycle. • As part of this cycle the element nitrogen forms parts of the compounds in the cells of all living things. (proteins) • Nitrogen gas is continual released back into the atmosphere by the action of bacteria in the soil.

38. Uses of Nitrogen • The fertilizer industry is the largest consumer of nitrogen, using it to make compounds such as ammonium sulphate, ammonium nitrate and ammonia. • Due to its low reactivity it can be used as an unreactive O2 free atmosphere for the electronics industry, glass making and welding.

39. It is used to remove flammable vapours from oil pipelines and tanks and the refuelling tubes for planes during flight. • It is also used to store fruit. • Because of its low boiling point (-196C) it is suitable for the storage of frozen eggs, sperm and embryos, for snap freezing foods and the cooling of super conductors.

40. Commercial Production of Nitrogen • Like oxygen nitrogen is one of the most important chemicals in terms of quantity produced each year. Properties of nitrogen • a colourless and odourless gas • insoluble in water • generally unreactive

41. Oxides of Nitrogen • Nitrogen forms a number of compounds with oxygen. We are only going to look at 2 of these oxides nitrogen (II) oxide (NO) sometimes called nitric oxide and nitrogen (IV) oxide (NO2) sometimes called nitrogen dioxide.

42. Nitrogen (II) oxide (NO) • Forms when nitrogen and oxygen are mixed at extremely high temperatures, which can be generated by lightning flashes or meteor trails. They can also be reached in volcanoes and in combustion engines.

43. This colourless gas is very difficult to isolate as it reacts readily with oxygen in the air to form the brown poisonous nitrogen (IV) oxide (NO2). Similar reactions as those talked about are responsible for the formation of a mixture of NO and NO2 known as NOx from the combustion of fossil fuels.

44. Lab preparation of NO NO can be prepared by a reaction between copper and 50% nitric acid solution: NO is only slightly soluble so can be collected by the displacement of water (same as oxygen gas).

45. Apparatus for the preparation of NO

46. Nitrogen(VI) oxide (NO2) • Formed in the biosphere by the reaction of NO with oxygen. • It is a brown toxic gas • Chemically reactivity • It is an acidic oxide, which dissolves in water to form a mixture of nitric and nitrous acids. Nitrous Acid Nitric Acid

47. Laboratory preparation of NO2 • Can be made in the lab from the reaction between concentrated nitric acid and copper. • As the gas is soluble, it is collected by the upwards displacement of air

48. Noble Gases • These are the elements in Group VIII of the Periodic Table, (Ne, Ar, Kr, Xe and Rn) • All exist as discrete atoms • Have low melting and boiling temperatures. • Thought for a long time to be chemically inert but recently there have been compounds of Xe and Kr formed. • Low reactivity is due to there stable outer shell.

49. Abundance and Uses

50. Gaseous Waste • One of the major problems of modern times is the gaseous waste produced from the burning of fossil fuels. • Fossil fuels are used in power stations to make electricity, to heat homes and offices, and to power different forms of transport. • Although there are other sources of gaseous waste, it has been estimated that 60% of those over major cities like Melbourne have been produced by the internal combustion engine of motor vehicles. Look at the table on the next slide.