Air science chem_na_elearning

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Air science chem_na_elearning

  1. 1. Air
  2. 2. Our atmosphere has been taken for granted in the past. In the last few decades, scientists and the general public began to realise the adverse effects of pollutants on the air we breathe. It is now recognised that pollutants such as sulfur dioxide, oxides of nitrogen, and particulates released into the atmosphere as a result of energy generation and increased use of motor vehicles, have serious health and environmental consequences. In this section, the sources of air pollutants and their effects are examined. Students should be able to value the knowledge of the hazardous nature of pollutants and the environmental issues related to air pollution. Overview
  3. 3. Course Syllabus <ul><li>At the end of this chapter, you should be able to: </li></ul><ul><li>describe the volume composition of gases present in dry air as 79% nitrogen, 20% oxygen and the remainder being noble gases (with argon as the main constituent) and carbon dioxide </li></ul><ul><li>name some common atmospheric pollutants e.g. carbon monoxide; methane; nitrogen oxides (NO and NO 2 ); ozone; sulfur dioxide; unburned hydrocarbons </li></ul>
  4. 4. Course Syllabus <ul><li>At the end of this chapter, you should be able to: </li></ul><ul><li>state the sources of these pollutants as </li></ul><ul><ul><li>carbon monoxide from incomplete combustion of carbon-containing substances </li></ul></ul><ul><ul><li>nitrogen oxides from lightning activity and internal combustion engines </li></ul></ul><ul><ul><li>sulfur dioxide from volcanoes and combustion of fossil fuels </li></ul></ul>
  5. 5. Course Syllabus <ul><li>At the end of this chapter, you should be able to: </li></ul><ul><li>discuss some of the effects of these pollutants on health and the environment </li></ul><ul><ul><li>the poisonous nature of carbon monoxide </li></ul></ul><ul><ul><li>the role of nitrogen dioxide and sulfur dioxide in the formation of “acid rain” and </li></ul></ul><ul><ul><li>its effects on respiration and buildings </li></ul></ul>
  6. 6. Why is air important to us??
  7. 7. http://straitstimes.asia1.com.sg/sub/latest/story/0,5562,302121,00.html? Feb 20, 2005 FIFTY FIREFIGHTERS STRUGGLED AGAINST THE WIND to bring the blaze in a forested area under control by 7pm but several pockets of fire remained because it was so windy. No one was injured. - ASHLEIGH SIM Firemen have been putting out an average of about six bush fires a day since January due to the heat. - SEAN TAN Feb 19, 2005
  8. 8. 23 Sept, 1997 22 Sept, 1997 18 Sept, 1997 17 Sept, 1997 14 Sept, 1997 12 Sept, 1997 http://mrdata.com/~blakef/galleries/SingaporeHaze/haze.html
  9. 9. Good air is important for health. <ul><li>Harm caused by haze: </li></ul><ul><li>Breathing problems, particularly for people with asthma </li></ul><ul><li>Interference with aircraft landings due to poor visibility, some airlines had to delay or cancel their flights </li></ul><ul><li>Tourism industry suffers as visitors stay away. </li></ul><ul><li>“ So, what air consists of?” </li></ul>
  10. 10. composition of air Air is a mixture of gases. <ul><li>contains 79% nitrogen </li></ul><ul><li>contains 20% oxygen </li></ul><ul><li>contains 1% other gases (including argon, carbon dioxide and water vapour) </li></ul>Check this out! http://sunshine.chpc.utah.edu/labs/atmosphere/atm_gases1.html argon (1%) oxygen (20%) nitrogen (79%)
  11. 12. What happens when things burn? <ul><li>Elements combined with oxygen to produce oxides. </li></ul><ul><li>C + O 2  CO 2 </li></ul><ul><li>2Cu + O 2  2CuO </li></ul><ul><li>2H 2 + O 2  2H 2 O </li></ul><ul><li>2Mg + O 2  2MgO </li></ul><ul><li>S + O 2  SO 2 </li></ul>
  12. 13. oxygen <ul><li>combustion is a reaction in which substances react with oxygen in an exothermic reaction </li></ul><ul><li>burning happens when flames are given out during combustion </li></ul>combustion Oxygen is obtained from air. It is compressed and stored in cylinders or kept as liquid in insulated tanks. Some amount of oxygen can be produced in the laboratory through the decomposition of hydrogen peroxide.
  13. 14. oxygen <ul><li>products of combustion are oxides </li></ul><ul><li>examples: </li></ul>combustion water, H 2 O colourless liquid explosion and flash of light hydrogen magnesium oxide, MgO white solid burns with very bright white light magnesium carbon dioxide, CO 2 colourless gas with no smell solid burns with bright red glow carbon burns with blue flame powder burns with dull red glow What is Observed colourless gas with strong smell black solid Appearance of Product sulfur dioxide, SO 2 sulfur copper Element copper(II) oxide, CuO Name and Formula of Product
  14. 15. <ul><li>Fuels are burnt to provide energy. </li></ul><ul><li>Examples of fuels are compounds like hydrocarbon. </li></ul><ul><li>Hydrocarbons are simply compounds containing hydrogen and carbon. </li></ul><ul><li>The products formed from the combustion of hydrocarbons depend on certain conditions. </li></ul><ul><li>If there is sufficient oxygen , there will be complete combustion, producing carbon dioxide and water . </li></ul>combustion oxygen
  15. 16. To show that carbon dioxide and water are produced when a candle burns in air. Hydrocarbon + oxygen  carbon dioxide + water vapour hydrocarbon
  16. 17. To show that carbon dioxide and water are produced when a candle burns in air. Hydrocarbon + oxygen  carbon dioxide + water vapour
  17. 18. oxygen incomplete combustion <ul><li>occurs when combustion of hydrocarbons is incomplete due to lack of oxygen </li></ul><ul><li>produces two other substances: soot and carbon monoxide </li></ul><ul><li>effects of incomplete combustion can be seen in the laboratory Bunsen burner </li></ul>complete combustion air-hole opened (complete combustion) pale blue (gas burning completely) blue (unburnt gas) air-hole closed (incomplete combustion) yellow flame due to hot specks of unburnt carbon incomplete combustion
  18. 19. Combustion without enough oxygen Which Bunsen burner has the air valve open? Which Bunsen burner has less oxygen available to react with the fuel - methane? What two products are normally formed during the combustion of a fuel? A B
  19. 20. oxygen <ul><li>comparing complete combustion and incomplete combustion of hydrocarbons: </li></ul>complete & incomplete combustion Combustion is rarely complete when carbon compounds burn in air and carbon monoxide and soot produced can cause air pollution. shortage of oxygen to burn plenty of oxygen to burn example: flame of a bunsen burner with air-hole opened products are CO 2 and H 2 O Complete Combustion example: flame of a bunsen burner with air-hole closed products include soot (C) and carbon monoxide (CO) Incomplete Combustion
  20. 21. Do you know… <ul><li>People have been burning candles for thousands of years. Unknown to them, the soot produced contains tiny football-shaped molecules of carbon, each with 60 carbon atoms, and also a few rugby-ball-shaped molecules with 70 carbon atoms. It is a new form of carbon only discovered in 1985. Smoky Bunsen flames have them as well! </li></ul><ul><li>The reason why they were not found earlier is that few of these molecules survive the flames! </li></ul>
  21. 22. <ul><li>Respiration is the oxidation of sugars in our bodies to produce energy. </li></ul>respiration <ul><li>when we breathe, the blood in our lungs takes in oxygen </li></ul><ul><li>oxygen will then react with sugars in our bodies to produce energy and carbon dioxide </li></ul>sugar + oxygen carbon dioxide + water + energy oxidation of sugars in our bodies to provide energy for games comes from the food we eat will be breathed out oxygen
  22. 23. <ul><li>http:// app.mewr.gov.sg/home.asp?id =M1 </li></ul>air pollution
  23. 24. air pollution Air around us contains pollutants, which are harmful substances to the environment oxides of nitrogen methane carbon monoxide Pollutants lightning; vehicle engines bacterial decay of vegetation; farm animals and rice growing incomplete combustion of carbon fuels Major Sources fit vehicles with catalytic converters breathing difficulties; acid rain; produces ozone no easy solutions global warming supply excess air to ensure complete combustion; fit vehicles with catalytic converters headaches; breathing difficulties; can kill people Treatment or Prevention Harmful Effects
  24. 25. air pollution unburnt hydrocarbons sulfur dioxide ozone Pollutants vehicle engines combustion of fossil fuels – especially coal; volcanoes’ eruptions sunlight acting on unburnt hydrocarbons and nitrogen dioxide Major Sources fit vehicles with catalytic converters produces ozone burn less sulphur-containing fuels; absorb SO 2 from chimney gases with calcium carbonate breathing difficulties; asthma attacks; acid rain reduce vehicle emissions of pollutants irritates eyes and lungs; asthma attacks Treatment or Prevention Harmful Effects
  25. 26. <ul><li>colourless and odourless gas </li></ul><ul><li>some of the CO in the air is natural, from the result of forest fires. </li></ul>air pollution carbon monoxide (CO) <ul><li>comes from the incomplete combustion of fuel in vehicles; all new motor cars in Singapore are fitted with catalytic converters; oxidises CO to CO 2 </li></ul>
  26. 27. <ul><li>can be absorbed by haemoglobin in the blood, thus blood can no longer absorb O 2 </li></ul>carbon monoxide (CO) <ul><li>extra amounts of CO result in tiredness, headaches, heart damage and small amounts can be lethal </li></ul><ul><li>Before absorption of CO: </li></ul><ul><li>O 2 + haemoglobin oxyhaemoglobin </li></ul><ul><li>(moves through the body to release O 2 when needed) </li></ul><ul><li>After absorption of CO: </li></ul><ul><li>CO + haemoglobin carboxyhaemoglobin </li></ul><ul><li>(does not absorb O 2 ) </li></ul>air pollution
  27. 28. <ul><li>fuels (coal and petroleum) contain sulfur as an impurity; when fuels are burnt, sulfur is oxidised to SO 2 </li></ul>sulfur dioxide (SO 2 ) <ul><li>is also emitted from volcanoes’ eruptions </li></ul><ul><li>irritates the eyes and causes breathing difficulties; main cause of acid rain </li></ul>volcanoes: natural source of SO 2 pollution air pollution
  28. 29. <ul><li>in Singapore, there are measures to reduce the emission of SO 2 into the atmosphere: </li></ul>sulfur dioxide (SO 2 ) <ul><li>oil fuels are not allowed to contain more than 2% sulfur </li></ul><ul><li>exhaust gases from power stations and industries are treated with CaCO 3 to remove acidic SO 2 </li></ul>volcanoes: natural source of SO 2 pollution air pollution
  29. 30. sulfur dioxide (SO 2 ) <ul><li>Calcium carbonate are strongly heated and partly decomposed to give alkaline calcium oxide. </li></ul><ul><li>CaCO 3 (s)  CaO(s) + CO 2 (g) </li></ul><ul><li>The exhaust gases are treated with a wet mixture of calcium carbonate and calcium oxide. </li></ul><ul><li>CaCO 3 (s) + SO 2 (g)  CaSO 3 (s) + CO 2 (g) </li></ul><ul><li>CaO(s) + SO 2 (g)  CaSO 3 (s) </li></ul>air pollution
  30. 31. sulfur dioxide (SO 2 ) <ul><li>CaCO 3 (s) + SO 2 (g)  CaSO 3 (s) + CO 2 (g) </li></ul><ul><li>CaO(s) + SO 2 (g)  CaSO 3 (s) </li></ul><ul><li>Calcium sulfite react with air to from calcium sulfate, and then dumped. </li></ul><ul><li>Limestone is used because it is cheap. </li></ul>air pollution
  31. 32. <ul><li>At high temperatures, nitrogen and oxygen combine to form nitrogen monoxide: </li></ul><ul><li>N 2 (g) + O 2 (g)  2NO(g) </li></ul><ul><li>The nitrogen oxide combines with more oxygen to become nitrogen dioxide: </li></ul><ul><li>2NO(g) + O 2 (g)  2NO 2 (g) </li></ul><ul><li>These two oxides of nitrogen are often describe simply as NO x . </li></ul>nitrogen oxides (NO and NO 2 ) air pollution
  32. 33. <ul><li>oxides of nitrogen (NO and NO 2 ) are produced naturally in lightning and forest fires </li></ul><ul><li>excess man-made production of oxides of nitrogen is harmful; found inside motorcar engines, power stations and industries </li></ul><ul><li>damage people’s lungs and react with other pollutants to form ozone </li></ul>air pollution nitrogen oxides (NO and NO 2 )
  33. 34. <ul><li>preventive measure: motorcars are fitted with catalytic converters to reduce oxides of nitrogen to N 2 </li></ul><ul><ul><li>Not in syllabus: the redox reactions in Catalytic Converter to remove combustion pollutants. </li></ul></ul>air pollution nitrogen oxides (NO and NO 2 )
  34. 35. Quick Check <ul><li>Car exhaust fumes are a major source of air pollution. What pollutants are present in car exhaust? </li></ul><ul><li>Answer: </li></ul><ul><li>Carbon monoxide, sulfur dioxide, oxides of nitrogen and unburnt hydrocarbons are present in car exhaust fumes. </li></ul>Key Carbon monoxide Unburnt hydrocarbons sulfur dioxide Oxides of nitrogen Smoke and soot
  35. 36. <ul><li>sulfur dioxide (SO 2 ) and nitrogen dioxide (NO 2 ) are acidic oxides that react with oxygen and water vapour in the air to form sulphuric acid and nitric acid which become acid rain </li></ul>acid rain air pollution SO 2 + oxygen + water vapour NO 2 + oxygen + water vapour sulphuric acid nitric acid acid rain atmosphere acidic oxides
  36. 37. <ul><li>typical pH of acid rain is 4 which is 1000 times more acidic than clean water </li></ul><ul><li>Pure water has a pH of 7, and rainwater has a pH of 5.6. </li></ul>acid rain air pollution acid corrodes buildings and metal structures soils acidified acid kills fish lakes acidified acid damages trees through roots gases damage green leaves sulphuric acid nitric acid ACID RAIN gases react with air and water in clouds coal, oil, fossil fuels burned
  37. 38. acid rain <ul><li>harmful effects: </li></ul><ul><li>corrodes the cement and stones used in buildings </li></ul><ul><li>corrodes the steel structures such as fences and bridges </li></ul><ul><li>kills fishes in fresh water lakes </li></ul><ul><li>makes agricultural land acidic thus crops grow poorly </li></ul>damage to left statue caused by acid rain air pollution
  38. 40. acid rain <ul><li>prevention: </li></ul><ul><li>burn fuels that contain less sulFur </li></ul><ul><li>(which is why oil and natural gas is preferred instead of coal for power stations) </li></ul><ul><li>neutralise acidic oxides from power stations with alkalis before they are released into the atmosphere </li></ul><ul><li>fit motor cars with catalytic converters to reduce the emission of nitrogen oxides </li></ul><ul><li>adding calcium hydroxide to lakes and soils to neutralise the acid </li></ul>air pollution
  39. 41. acid rain NOTE: These methods are not very effective as the damage has already been done. The only effective way to halt acid rain damage is to stop releasing acidic oxides into the air. air pollution
  40. 42. Question 1 <ul><li>Which is the most common gas in air? </li></ul><ul><ul><li>Ar </li></ul></ul><ul><ul><li>CO 2 </li></ul></ul><ul><ul><li>O 2 </li></ul></ul><ul><ul><li>H 2 O </li></ul></ul><ul><ul><li>Answer: C </li></ul></ul>
  41. 43. Question 2 <ul><li>Which pollutant causes the greatest corrosion of steel structures? </li></ul><ul><ul><li>Carbon monoxide </li></ul></ul><ul><ul><li>Methane </li></ul></ul><ul><ul><li>Ozone </li></ul></ul><ul><ul><li>Sulfur dioxide </li></ul></ul><ul><ul><li>Answer: D </li></ul></ul>
  42. 44. Question 3 <ul><li>What is a natural source of sulfur dioxide pollution in the atmosphere? </li></ul><ul><ul><li>combustion of diesel fuel </li></ul></ul><ul><ul><li>volcanoes </li></ul></ul><ul><ul><li>lightning </li></ul></ul><ul><ul><li>incomplete combustion of methane </li></ul></ul><ul><ul><li>Answer: B </li></ul></ul>
  43. 45. Question 4 <ul><li>Molecules present in the exhaust gases from a motorcar engine include argon, carbon dioxide, carbon monoxide, methane, nitrogen, nitrogen dioxide and water vapour. Which of these gases are also found in unpolluted air? </li></ul><ul><ul><li>nitrogen only </li></ul></ul><ul><ul><li>nitrogen, carbon dioxide and water vapour only </li></ul></ul><ul><ul><li>argon, methane, nitrogen, and water vapour only </li></ul></ul><ul><ul><li>argon, nitrogen, nitrogen dioxide, carbon dioxide and water vapour only </li></ul></ul><ul><ul><li>Answer: D </li></ul></ul>
  44. 46. Question 5 <ul><li>Which pollutants can be removed from the chimney gases of factories and power stations by treatment with calcium carbonate? </li></ul><ul><ul><li>carbon monoxide and sulfur dioxide </li></ul></ul><ul><ul><li>nitrogen dioxide and sulfur dioxide </li></ul></ul><ul><ul><li>methane and ozone </li></ul></ul><ul><ul><li>nitrogen dioxide only </li></ul></ul><ul><ul><li>Answer: B </li></ul></ul>
  45. 47. Acknowledgement: <ul><li>www.longman.com </li></ul><ul><li>Marshall Cavendish International (Singapore) Pte. Ltd. </li></ul>

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