11/5/20091C118 November 6thAcid Rain Sections 6.6‐6.131)pH of rain due to atmospheric CO1)pH of rain due to atmospheric CO22) Sources of extra acidity “Acid” Rain is pH < 5.3Sources and Emission trendsChapter 6 End of Chapter Problems:15, 17, 18, 21, 22, 23, 34, 36, 40 pH of rainfall in 2002 Measured at Central Analytical LaboratoryNational Atmospheric Deposition Program National Trends http://nadp.sws.uiuc.edupH of rain is _________ everywhere.11/5/20092Group Work/Clicker Question• You would like to know the Kavalue for carbonic acid (HCO) to understand how atmospheric CO(H2CO3) to understand how atmospheric CO2concentrations affect the pH of rain. • In the laboratory, you prepare a 0.1 M solution of carbonic acid (H2CO3) and measure the pH to be 3673.67.• Calculate the Kaof carbonic acid.1) H2CO3↔ H++ HCO3‐I0.1 00C ‐x+x+xE0.1‐xxx2) The value of x can be found because the pH is known to be 3.67. 3.67 = ‐log[H+] Therefore, [H+] = 10 ‐3.67 = 2.14 x 10‐4M3) Plug in values to solve for Ka[][][]7424323105.4)101.21.0()1014.2(−−−−+=−== xxxCOHHCOHKa11/5/20093Calculating the pH of unpolluted rainAtmospheric carbon dioxide has a concentration f 382If th Kf bi id i 45of 382 ppm. If the Kafor carbonic acid is 4.5 x 10‐7, calculate the pH of rain.Part I: Concentration of carbonic acid in rain.Part II Weak acid problemPart II: Weak acid problem. Part I: Concentration of carbonic acid in rainHenry’s Law:Ps=ksS = P = k (CO2) = 29.4 (L atm/mol)11/5/20094Part II: Weak acid problemfor pH of unpolluted rain“Extra” AciditypH < 5.3SOxfrom burning coalCoal: CHONSCoal: C135H96O9NS1) S (s) + O2(g) → SO2 (g)2) SO2(g) + H2O (l) → H2SO3(aq) (sulfurous acid)3) 2 SO2(g) + O2(g) → 2 SO3(g)slow )2(g)2(g)3(g)4) SO3(g) + H2O (l) → H2SO4(aq) fast (sulfuric acid)Other factors that play a role in facilitating formation of H2SO4from SO2. (O3, OH, sunlight)11/5/20095“Extra” AciditypH < 5.3NOxfrom combustion in general1) N2+ O2→ 2 NO (what causes this reaction?)2) NO → NO2(facilitated by?) 3) NO2+ OH → HNO3(nitric acid)(nitric acid)LA BasinVery low sulfur, but high NOx.In January 1982 the fog near the Rose Bowl in Pasadena was found to haveIn January 1982, the fog near the Rose Bowl in Pasadena was found to have A pH = 2.5. Breathing it would have been like inhaling a fine mist of vinegar. 11/5/20096Nitrate and Sulfate Ions in RainDo high nitrate and sulfate levels correlate with more acidic rain?Current Sources of SOx and NOxUS Emissions in 2002SOx NOxCoal burning electric utility plantSource: EPA, Air Trends11/5/20097How much SO2does the U.S. emit?In, 2006 the U.S. burned about 1.1 billion tons of coal. Assuming it was 3% sulfur by weight, calculate the tons of SO2emitted.Trends in Emission of NOXand SOxin the U.S.11/5/20098Reasons for decrease in emissions: NOx2) G hitth li1) 2) Green chemistry technologiesA. Glass manufacturingPraxair Inc. substitutes 100% oxygen for air in furnace used to heat glassResult: Decreases NO production by 90%Decreases energy consumption by 50%gy p yGlass manufacturers using this technology save enough energy to meet daily needs of 1 million AmericansB. Low NOx burners are now in place on 75% of coal burning plantsDecrease air during combustion so less NO is producedReasons for decrease in emissions: SOxAnthracite or “hard coal” is found in Pennsylvania and has a high heat content and low sulfur.Problem: supply is basically gonepp y y gBituminous or “soft coal” is abundant in the midwest and has high heat content but high sulfur (3‐5%)Western coal has low sulfur, sub bituminous coal, but has low heat content2) Crush coal to a fine powder, wash with water so that heavy sulfur containing minerals sink to the bottom.Problem: expensive and only removes half of sulfur3) 2 SO2(g) + O2(g) + 2 CaCO3(s) → 2 CaSO4+ 2 CO211/5/20099Which method was used to meet requirements of 1990 Clean Air Act Amendments?Changes in Emissions as a Result of Clean Coal Technology11/5/200910Major eruptions such asMt. Pintubo in 1991can add much moreHow do manmade emissions compare to natural