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Class22 - Adverse Effects of Current Technologies on...

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Adverse Effects of Current Technologies on Atmosphere International Concerns: I. Acid Rain II. Ozone Depletion III. Climate Change (Global Warming)
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Tro, page 327 [H + ] = 10 -pH Increasingly Acidic Increasingly Basic pH = -log 10 [H + ] or [H + ] = 10 -pH [H + ] http://www.uvprocess.com/product.asp?code=PH+++++++B I. Acid Rain: pH quantifies acidity
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pH of common substances (average) http://wpcontent.answers.com/wikipedia/commons/thumb/4/46/PH_scale.png/350px-PH_scale.png Pure water has a pH = 7 Natural rainwater has a pH 5.6 due to H 2 CO 3 Acid rain has a pH < 5.6 due to presence of additional acid(s): HNO 3 and/or H 2 SO 4 .
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Acid rain is defined as rain having a pH < 5.6 pH of rain depends on presence/absence of three oxides in air: CO 2 , NO 2 , and SO 3 These oxides react with rain water to produce acids: H 2 CO 3 , HNO 3 , and H 2 SO 4 ; respectively Natural rain contains only H 2 CO 3 and has an acidity of pH 5.6 Acid rain contains H 2 CO 3 plus HNO 3 and/or H 2 SO 4 and has a pH < 5.6
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http://nadp.sws.uiuc.edu/isopleths/maps1999/phfield.gif All rain falling on US is acidic (pH < 7), but only rain having pH < 5.6 is defined as acid rain Record low pH
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http://portal.unesco.org/education/en/file_download.php/139c5df78bcee496e053ef6052c4a5e3How+acid+rain+is+formed+frame.jpg *Dry deposition - gas adsorbs onto surface of particulate matter. Forms acidic solutions when later contacted by water. Makes up about 50% of deposition. * Source of acid rain is combustion of fossil fuels
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CaCO 3 + H + Ca 2+ + HCO 3 - Limestone reacts with acids: Unprotected areas: Al 2 Si 2 O 5 (OH) 4 + 6 H + 2 Al 3+ + 2 SiO 2 + 5 H 2 O (Clay) (toxic) Adverse effects of acid rain on lithosphere and hydrosphere are decreased by limestone Buell/Girard, Chemistry, Prentice Hall, NJ, 1994, 232 Figure. Uncolored areas are protected by natural limestone deposits.
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Figure. Marble tombstone that has been exposed to acid rain in England since 1817. Raven et al, Environment, Saunders, NY, 1995, 450 Acid rain dissolves marble statues and monuments: CaCO 3 + H + Ca 2+ + HCO 3 - Adverse effect of acid rain on materials
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Schwartz et al, Chemistry in Context, ACS, DC, 1994, 171 Buell/Girard, Chemistry, Prentice Hall, NJ, 1994, 232 Acid rain releases toxic Al 3+ ions that kill trees and fish
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Clean Air Act amendments (1990) deal with acid rain by mandating reductions in its precursors: SO 2 and NO 2 . EPA plans to cut emissions of both gases from coal-fired power plants significantly by 2014 to reduce pollution in states downwind from power plants. (C&EN, 7/11/11/, pg 5.) http://www.epa.gov/airtrends/sulfur.html http://www.epa.gov/airtrends/nitrogen.html
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Chang, Chemistry, 5th, McGraw Hill, NY, 1994, 727 CaCO 3 + H + Ca 2+ + HCO 3 - Remediation: limestone can be added to soil
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