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Air

Air.

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Air

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  1. Air

  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. Why is air important to us??

  4. 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 Feb 19, 2005 Firemen have been putting out an average of about six bush fires a day since January due to the heat. - SEAN TAN http://straitstimes.asia1.com.sg/sub/latest/story/0,5562,302121,00.html?

  5. 12 Sept, 1997 14 Sept, 1997 17 Sept, 1997 18 Sept, 1997 22 Sept, 1997 23 Sept, 1997 http://mrdata.com/~blakef/galleries/SingaporeHaze/haze.html

  6. Good air is important for health. • Harm caused by haze: • Breathing problems, particularly for people with asthma • Interference with aircraft landings due to poor visibility, some airlines had to delay or cancel their flights • Tourism industry suffers as visitors stay away. • “So, what air consists of?”

  7. argon (1%) nitrogen (79%) oxygen (20%) composition of air Air is a mixture of gases. • contains 79% nitrogen • contains 20% oxygen • contains 1% other gases (including argon, carbon dioxide and water vapour) Check this out! http://sunshine.chpc.utah.edu/labs/atmosphere/atm_gases1.html

  8. What happens when things burn? • Elements combined with oxygen to produce oxides. • C + O2 CO2 • 2Cu + O2  2CuO • 2H2 + O2  2H2O • 2Mg + O2  2MgO • S + O2  SO2

  9. oxygen combustion is a reaction in which substances react with oxygen in an exothermic reaction burning happens when flames are given out during combustion 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.

  10. oxygen products of combustion are oxides examples: combustion

  11. oxygen combustion • Fuels are burnt to provide energy. • Examples of fuels are compounds like hydrocarbon. • Hydrocarbons are simply compounds containing hydrogen and carbon. • The products formed from the combustion of hydrocarbons depend on certain conditions. • If there is sufficient oxygen, there will be complete combustion, producing carbon dioxide and water.

  12. hydrocarbon To show that carbon dioxide and water are produced when a candle burns in air. Hydrocarbon + oxygen  carbon dioxide + water vapour

  13. To show that carbon dioxide and water are produced when a candle burns in air. Hydrocarbon + oxygen  carbon dioxide + water vapour

  14. oxygen pale blue (gas burning completely) yellow flame due to hot specks of unburnt carbon blue (unburnt gas) air-hole opened (complete combustion) air-hole closed (incomplete combustion) complete combustion incomplete combustion incomplete combustion • occurs when combustion of hydrocarbons is incomplete due to lack of oxygen • produces two other substances: soot and carbon monoxide • effects of incomplete combustion can be seen in the laboratory Bunsen burner

  15. A B Combustion without enough oxygen Which Bunsen burner has the air valve open? What two products are normally formed during the combustion of a fuel? Which Bunsen burner has less oxygen available to react with the fuel - methane?

  16. oxygen comparing complete combustion and incomplete combustion of hydrocarbons: complete & incomplete combustion Combustion is rarely complete when carbon compounds burn in air and carbon monoxide and soot produced can cause air pollution.

  17. Do you know… 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! The reason why they were not found earlier is that few of these molecules survive the flames!

  18. Respiration is the oxidation of sugars in our bodies to produce energy. oxygen respiration • when we breathe, the blood in our lungs takes in oxygen • oxygen will then react with sugars in our bodies to produce energy and carbon dioxide sugar + oxygen carbon dioxide + water + energy will be breathed out comes from the food we eat oxidation of sugars in our bodies to provide energy for games

  19. http://app.mewr.gov.sg/home.asp?id=M1 air pollution

  20. air pollution Air around us contains pollutants, which are harmful substances to the environment

  21. air pollution

  22. air pollution carbon monoxide (CO) • colourless and odourless gas • some of the CO in the air is natural, from the result of forest fires. • comes from the incomplete combustion of fuel in vehicles; all new motor cars in Singapore are fitted with catalytic converters; oxidises CO to CO2

  23. air pollution carbon monoxide (CO) • can be absorbed by haemoglobin in the blood, thus blood can no longer absorb O2 • Before absorption of CO: • O2 + haemoglobin oxyhaemoglobin • (moves through the body to release O2 when needed) • After absorption of CO: • CO + haemoglobin carboxyhaemoglobin • (does not absorb O2) • extra amounts of CO result in tiredness, headaches, heart damage and small amounts can be lethal

  24. air pollution sulfur dioxide (SO2) • fuels (coal and petroleum) contain sulfur as an impurity; when fuels are burnt, sulfur is oxidised to SO2 • is also emitted from volcanoes’ eruptions • irritates the eyes and causes breathing difficulties; main cause of acid rain volcanoes: natural source of SO2 pollution

  25. air pollution sulfur dioxide (SO2) • in Singapore, there are measures to reduce the emission of SO2 into the atmosphere: • oil fuels are not allowed to contain more than 2% sulfur • exhaust gases from power stations and industries are treated with CaCO3 to remove acidic SO2 volcanoes: natural source of SO2 pollution

  26. air pollution sulfur dioxide (SO2) • Calcium carbonate are strongly heated and partly decomposed to give alkaline calcium oxide. CaCO3(s)  CaO(s) + CO2(g) • The exhaust gases are treated with a wet mixture of calcium carbonate and calcium oxide. CaCO3(s) + SO2(g)  CaSO3(s) + CO2(g) CaO(s) + SO2(g)  CaSO3(s)

  27. air pollution sulfur dioxide (SO2) CaCO3(s) + SO2(g)  CaSO3(s) + CO2(g) CaO(s) + SO2(g)  CaSO3(s) • Calcium sulfite react with air to from calcium sulfate, and then dumped. • Limestone is used because it is cheap.

  28. air pollution nitrogen oxides (NO and NO2) • At high temperatures, nitrogen and oxygen combine to form nitrogen monoxide: N2(g) + O2(g)  2NO(g) • The nitrogen oxide combines with more oxygen to become nitrogen dioxide: 2NO(g) + O2(g)  2NO2(g) • These two oxides of nitrogen are often describe simply as NOx.

  29. air pollution nitrogen oxides (NO and NO2) • oxides of nitrogen (NO and NO2) are produced naturally in lightning and forest fires • excess man-made production of oxides of nitrogen is harmful; found inside motorcar engines, power stations and industries • damage people’s lungs and react with other pollutants to form ozone

  30. air pollution nitrogen oxides (NO and NO2) • preventive measure: motorcars are fitted with catalytic converters to reduce oxides of nitrogen to N2 • Not in syllabus: the redox reactions in Catalytic Converter to remove combustion pollutants.

  31. Car exhaust fumes are a major source of air pollution. What pollutants are present in car exhaust? Answer: Carbon monoxide, sulfur dioxide, oxides of nitrogen and unburnt hydrocarbons are present in car exhaust fumes. Carbon monoxide Unburnt hydrocarbons sulfur dioxide Oxides of nitrogen Smoke and soot Quick Check Key

  32. SO2 + oxygen + water vapour sulphuric acid NO2 + oxygen + water vapour nitric acid acidic oxides atmosphere acid rain air pollution acid rain • sulfur dioxide (SO2) and nitrogen dioxide (NO2) are acidic oxides that react with oxygen and water vapour in the air to form sulphuric acid and nitric acid which become acid rain

  33. gases react with air and water in clouds sulphuric acid nitric acid gases damage green leaves ACID RAIN acid corrodes buildings and metal structures lakes acidified coal, oil, fossil fuels burned soils acidified acid damages trees through roots acid kills fish air pollution acid rain • typical pH of acid rain is 4 which is 1000 times more acidic than clean water • Pure water has a pH of 7, and rainwater has a pH of 5.6.

  34. air pollution acid rain • harmful effects: • corrodes the cement and stones used in buildings • corrodes the steel structures such as fences and bridges • kills fishes in fresh water lakes • makes agricultural land acidic thus crops grow poorly damage to left statue caused by acid rain

  35. air pollution acid rain • prevention: • burn fuels that contain less sulFur • (which is why oil and natural gas is preferred instead of coal for power stations) • neutralise acidic oxides from power stations with alkalis before they are released into the atmosphere • fit motor cars with catalytic converters to reduce the emission of nitrogen oxides • adding calcium hydroxide to lakes and soils to neutralise the acid

  36. air pollution 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.

  37. Question 1 Which is the most common gas in air? • Ar • CO2 • O2 • H2O Answer: C

  38. Question 2 Which pollutant causes the greatest corrosion of steel structures? • Carbon monoxide • Methane • Ozone • Sulfur dioxide Answer: D

  39. Question 3 What is a natural source of sulfur dioxide pollution in the atmosphere? • combustion of diesel fuel • volcanoes • lightning • incomplete combustion of methane Answer: B

  40. Question 4 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? • nitrogen only • nitrogen, carbon dioxide and water vapour only • argon, methane, nitrogen, and water vapour only • argon, nitrogen, nitrogen dioxide, carbon dioxide and water vapour only Answer: D

  41. Question 5 Which pollutants can be removed from the chimney gases of factories and power stations by treatment with calcium carbonate? • carbon monoxide and sulfur dioxide • nitrogen dioxide and sulfur dioxide • methane and ozone • nitrogen dioxide only Answer: B

  42. Acknowledgement: • www.longman.com • Marshall Cavendish International (Singapore) Pte. Ltd.

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