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Chemistry and the Environment

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  1. Chapter 46 Chemistry and the Environment 46.1Introduction 46.2Air Pollution 46.3Water Pollution 46.4Solid Waste 46.5Pollution Control in Hong Kong

  2. 46.1 Introduction (SB p.220) Pollution found in Hong Kong

  3. 46.1 Introduction (SB p.220) Pollution is the introduction of waste matter or energy into the environment by humans. It causes damages or deterioration to living systems and/or the environment A pollutant refers to any substance or energy produced through human activities which, at an unacceptable level, causes damages to the environment or is harmful to living systems

  4. 46.2 Air Pollution (SB p.221) Major Air Pollutants and their Sources • Major air pollutants in the modern city are CO(g), SO2(g), NOx(g) and small particulates(e.g. soot and lead) • Produced by burning fossil fuels in car engines, industrial plants and power plants

  5. 46.2 Air Pollution (SB p.221) • 1. Carbon monoxide • most common air pollutant in cities • produced by incomplete combustion of petrol, coal, and wood • e.g. C8H18(g) + 9O2(g)  • 3CO2(g) + 3CO(g) + 2C(s) + 9H2O(l)

  6. SO2 emitted when fossil fuels are burnt Power station 46.2 Air Pollution (SB p.222) • 2. Sulphur dioxide • produced by combustion of sulphur-containing fuels • large proportion of SO2 are generated at power stations, metal smelters in which sulphur-containing fuels are used

  7. 46.2 Air Pollution (SB p.222) • 3. Nitrogen oxide • produced when fuels are burnt at high temperatures • the level of NOx is noticeably high because of high-proportions of diesel-driven vehicles running • diesel engines produce less CO but a lot more NOx • 4. Hydrocarbons • formed by evaporation of organic materials, e.g. petrol, diesel, etc • found in car exhaust as unburnt hydrocarbons

  8. 46.2 Air Pollution (SB p.222) • 5. Ozone • produced by the reaction of oxygen gas with free oxygen atoms which are formed from the reaction between NOx and hydrocarbons in sunlight • O2(g) + O •  O3(g)oxygen radical

  9. 46.2 Air Pollution (SB p.222) • 6. Particulates • include black smoke (fine carbon particles), dust and soot (coarse carbon particles), so small that remain suspend in air for a long period of time • produced during operations in incinerators, factories, diesel vehicles, construction sites and coal or charcoal burners

  10. 46.2 Air Pollution (SB p.223) Source of CO

  11. 46.2 Air Pollution (SB p.223) Source of SO2

  12. 46.2 Air Pollution (SB p.223) Source of NOx

  13. 46.2 Air Pollution (SB p.223) Source of particulates

  14. Lichens cannot grow in seriously polluted air 46.2 Air Pollution (SB p.224) Effects of Polluted Air on the Environment • High levels of pollutants can cause headaches, nausea, irritation of the eyes, nose and throat and ill-feeling generally • Some pollutants may lead to respiratory diseases • Some plants like lichens will not grow in cities because of high levels of pollutants as they are more sensitive to O3 and SO2 than humans.

  15. 46.2 Air Pollution (SB p.224) • 1. Carbon monoxide • poisonous, colourless, tasteless and odourless gas • when one inhales it, it will enter the blood stream and bind preferentiallytohaemoglobin in the red blood cells replacing O2 •  reduction of O2 supply to organs and tissues •  causes death even in relatively low concentrations

  16. The plant on the left (from Germany) is damaged by acid rain 46.2 Air Pollution (SB p.224) • 2. Sulphur dioxide • colourless, toxic gas • cause impairment of the respiratory function, aggravation of existing respiratory diseasesand cardiovascular diseases • form acid rain • damage buildings and forests

  17. 46.2 Air Pollution (SB p.224) • 3. Nitrogen dioxide • reddish brown, toxic gas with pungent smell • irritate lungs, lower the resistance to respiratory infections • gives rise to photochemical smog • impair lung development in young children • form acid rain

  18. 46.2 Air Pollution (SB p.225) • 4. Hydrocarbons • causes photochemical smog • some hydrocarbons (e.g. benzene) are known as carcinogens • 5. Ozone • irritate respiratory system causing cough, chest pain and throat and eyes irritation and increase susceptibility to respiratory infections • damage plants

  19. 46.2 Air Pollution (SB p.225) • 6. Particulates • environmental impact depends on size and nature • very fine particles (diameter less than 1 m) are the most hazardous∵ cannot be filtered by hairs and mucus in the nose and the respiratory track. • drawn deep into the lungs •  impair lung functions, hinder the gas exchange, damage the lung tissue and cause respiratory illness

  20. 46.2 Air Pollution (SB p.225) The sources and effects of some air pollutants

  21. 46.2 Air Pollution (SB p.225) The sources and effects of some air pollutants (cont’d)

  22. 46.2 Air Pollution (SB p.226) • The harmful effects of pollutants depend on: • 1. Concentration & • 2. The duration of exposure • Take CO as an example: • If the concentration of CO is 600 – 700 ppm, inhaling it for an hour brings about barely detectable effects • The concentration of CO of 4000 ppm or higher can cause death in less than one hour • If the concentration of CO is 1000 ppm, the people will die from CO poisoning after inhaling for 4 hours

  23. 46.2 Air Pollution (SB p.226) Representation of Concentration of Pollutants • Parts per million (ppm) is one way to describe the concentration of pollutants • Thenumber of molecules of pollutants per million (106) molecules in air. (It is a ratio with no unit) • It isequal to the number of volumes of pollutants per million volumes of air based on the Avogadro’s law.

  24. 46.2 Air Pollution (SB p.226) • e.g. 50 ppm of CO means 50 cm3 of pollutant for every 1 000 000 cm3 of air • If the concentration is represented by percentage by volume, the unit is readily converted to ppm by multiplying with a factor of 10 000e.g. 0.1 % by volume = 1 000 ppm • The concentrations of pollutants are commonly expressed in g m–3 nowadays • Using ideal gas equation, PV = nRT, g m–3 and ppm can be interconverted

  25. 46.2 Air Pollution (SB p.226) Example 46-1 Express the concentration of 0.05 ppm carbon monoxide measured at 298 K (25°C) and 101 kPa (1 atm) in g m–3. (R.a.m. : C = 12.0, O = 16.0; ideal gas constant = 8.314 J K–1 mol–1) Answer

  26. Solution: In 1 m3 of air, there is m3 carbon monoxide. Using the ideal gas equation, PV = nRT where M is the molar mass of CO 46.2 Air Pollution (SB p.226)

  27. Solution: (cont’d) Mass of CO ∴ The concentration of carbon monoxide is 57.1 g m–3 46.2 Air Pollution (SB p.227)

  28. 46.2 Air Pollution (SB p.227) Check Point 46-1 (a) (i) State the major air pollutants. (ii) For each kind of pollutants, state one of the harmful effects. Answer

  29. 46.2 Air Pollution (SB p.227)

  30. (b) (i) 10 ppm =  100% = 0.001% ∴ 10 ppm NO2 equals 0.001% of NO2 by volume. 46.2 Air Pollution (SB p.227) Check Point 46-1 (cont’d) (b) Given that the temperature is 0°C and the pressure is 1 atm (i.e. 101 kPa), express the following concentrations of the gases in the units given. (i) Express 10 ppm NO2 in % by volume; (Ideal gas constant = 8.314 J K–1 mol–1; R.a.m.: N = 14.0, S = 32.0, O = 16.0, C = 12.0) Answer

  31. (b) (ii) In 1 m3 of air mass of SO2 = 854.4 g ∴ The concentration of SO2 is 854.4 g m–3 46.2 Air Pollution (SB p.227) Check Point 46-1 (cont’d) (b) Given that the temperature is 0°C and the pressure is 1 atm (i.e. 101 kPa), express the following concentrations of the gases in the units given. (ii) Express 0.3 ppm SO2 in g m–3; (Ideal gas constant = 8.314 J K–1 mol–1; R.a.m.: N = 14.0, S = 32.0, O = 16.0, C = 12.0) Answer

  32. (b) (iii) Let the volume of CO in 1 m3 of air be V. V = 8.03  10–6 m3 = =8.03 ppm 46.2 Air Pollution (SB p.227) Check Point 46-1 (cont’d) (b) Given that the temperature is 0°C and the pressure is 1 atm (i.e. 101 kPa), express the following concentrations of the gases in the units given. (iii) Express 10 000 g m–3 CO in ppm; (Ideal gas constant = 8.314 J K–1 mol–1; R.a.m.: N = 14.0, S = 32.0, O = 16.0, C = 12.0) Answer

  33. (b) (iv) Let the volume of SO2 in 1 m3 of air be V. V = 2.11  10–7 m3 % by volume = = 2.11  10–5 % 46.2 Air Pollution (SB p.227) Check Point 46-1 (b) Given that the temperature is 0°C and the pressure is 1 atm (i.e. 101 kPa), express the following concentrations of the gases in the units given. (iv) Express 600 g m–3 SO2 in % by volume. (Ideal gas constant = 8.314 J K–1 mol–1; R.a.m.: N = 14.0, S = 32.0, O = 16.0, C = 12.0) Answer

  34. 46.2 Air Pollution (SB p.230) Acid Rain • Unpolluted rainwater is slightly acidic, with pH value of about 5.7 • CO2(g) + H2O(l)  H2CO3(aq) pH  5.7 • Rainwater reacts with CO2 to form carbonic acid

  35. Rainwater with pH values lower than 5.7 is called acid rain • Acidic gaseous pollutants : SO2 and NO2 • In the atmosphere, SO2 is oxidized to SO3 slowly and then dissolves in rainwater readily • 2SO2(g) + O2(g) 2SO3(g) • SO3(g) + H2O(l)  H2SO4(aq) 46.2 Air Pollution (SB p.230)

  36. SO2(g) also dissolves in rainwater to form sulphuric(IV) acid • SO2(g) + H2O(l) H2SO3(aq) • H2SO3 will be further oxidized by atmospheric oxygen • 2H2SO3(aq) + O2(g)  2H2SO4(aq) 46.2 Air Pollution (SB p.230)

  37. 46.2 Air Pollution (SB p.230) • NO(g) is formed when burning fossil fuels in automobiles and power stations. • The NO(g) is then oxidized to NO2(g) 2NO(g) + O2(g)  2NO2(g) • In a series of complex reactions, NO2(g) is oxidized to HNO3(aq) 4NO2(g) + 2H2O(l) + O2(g)  4HNO3(aq)

  38. 46.2 Air Pollution (SB p.231) • Acid rain causes a lot of harmful effects on the environment • In water of pH lower than 4.5, calcium metabolism in freshwater fish will be affected, leading to poor health and stunted growth diversity and population of some freshwater species will be reduced • In soil of pH lower than 4.5, absorption of essential nutrients (e.g. K+, Ca2+and Mg2+) will be affected results in the death of plants

  39. The statue was corroded by acid rain 46.2 Air Pollution (SB p.231) • Acid rain also corrodes metals and accelerates the rate of deterioration of buildings, rocks and statues

  40. 46.2 Air Pollution (SB p.231) A summary of the formation and effects of acid rain

  41. 46.2 Air Pollution (SB p.232) Photochemical Smog • Photochemical smog is a mixture of pollutants including particulates, NOx, aldehydes, peroxyacetyl nitrate (PAN) and unreacted hydrocarbons, etc • Brownish haze that irritates our eyes is an indicator of photochemical smog • (Note: NO2 is responsible for the brown colour)

  42. in the presence of photochemical smog in the absence of photochemical smog 46.2 Air Pollution (SB p.232) Appearance of a city:

  43. NO2 from automobile exhaust absorbs sunlight and breaks down into NO and free O • NO2(g)  NO(g) + O(g) UV light 46.2 Air Pollution (SB p.232) • The formation of photochemical smog is initiated by sunlight and involves hydrocarbons and nitrogen oxides • The free O reacts with unburnt hydrocarbons, O2 and water vapour in a series of complex reaction to produce a variety of lachrymatory and toxic chemicals such as peroxyacetyl nitrate (PAN)

  44. 46.2 Air Pollution (SB p.233) • Principal reactions involved in the formation of photochemical smog (much simplified) • O(g) + O2(g)  O3(g)O(g) + hydrocarbons  aldehydesO3(g) + hydrocarbons  aldehydesHydrocarbons + O2(g) + NO2(g) lachrymatory substances, including PAN

  45. 46.2 Air Pollution (SB p.233) Formation of photochemical smog

  46. 46.2 Air Pollution (SB p.233) • The reactions of the formation of photochemical smog vary with altitude • ∵ wavelength of ultraviolet radiation from the sun determines which bonds are broken in the reaction

  47. 46.2 Air Pollution (SB p.233) • Photochemical smog causes headaches, eye, nose and throat irritation, worsening the lung function, coughing and wheezing • Ozone attacks the C = C linkage in rubber in a process known as ozonolysis. It cause rubbers and fabrics to deteriorate and car tyres to crack

  48. (a) (i) Acidic gaseous pollutants like sulphur dioxide and nitrogen dioxide are responsible for the formation of acid rain. In the atmosphere, sulphur dioxide is slowly oxidized to sulphur trioxide which dissolves readily in water droplets to form sulphuric(VI) acid. 2SO2(g) + O2(g) 2SO3(g) SO3(g) + H2O(l)  H2SO4(aq) When nitrogen monoxide is released to the atmosphere, it combines with atmospheric oxygen to form nitrogen dioxide. 2NO(g) + O2(g)  2NO2(g) In a series of complex reactions, nitrogen dioxide combines with oxygen and water vapour to form nitric(V) acid 4NO2(g) + 2H2O(l) + O2(g)  4HNO3(aq) 46.2 Air Pollution (SB p.233) Check Point 46-2 (a) Describe the chemical reactions involved in the formation of (i) acid rain; Answer

  49. (a) (ii) Photochemical smog is a mixture of pollutants including particulates, nitrogen oxides, ozone, aldehydes, peroxyacetyl nitrate (PAN) and unreacted hydrocarbons. Nitrogen dioxide from automobile exhaust first absorbs sunlight and breaks down into nitrogen monoxide and free oxygen atom which is very reactive. NO2(g)  NO(g) + O(g) The oxygen atom then reacts with other components of automobile exhaust (e.g. unburnt hydrocarbons) and those of the atmosphere (e.g. oxygen and water vapour) in a series of complex reactions to produce a variety of lachrymatory substances such as peroxyacetyl nitrate (PAN). 46.2 Air Pollution (SB p.233) Check Point 46-2 (a) Describe the chemical reactions involved in the formation of (ii) photochemical smog. Answer

  50. 46.2 Air Pollution (SB p.233) Very much simplified, some of the principal reactions in the formation of photochemical smog are as follows: O(g) + O2(g)  O3(g) O(g) + hydrocarbons  aldehydes O3(g) + hydrocarbons  aldehydes Hydrocarbons + O2(g) + NO2(g)  lachrymatory substances, including PAN