HSC Chemistry 2 Initial Notes

Part V Chemistry — Second Paper 91

Chapter 30 Environmental Chemistry 30.1 Key Concepts & Theoretical Foundations The atmosphere is a thin, layered envelope—troposphere, stratosphere, mesosphere, thermosphere—about 78% N2, 21% O2, 0.9% Ar and trace CO2, water vapour and pol- lutants. Human activity now measurably perturbs it. Four environmental problems Greenhouse effect: CO2, CH4, N2O, water vapour and CFCs absorb outgoing infrared and warm the surface. Ozone depletion: CFC- derived Cl radicals catalytically destroy stratospheric O3. Acid rain: SO2 and NOx form H2SO4/HNO3. Photochemical smog: NOx and hydrocarbons under sunlight give ozone, aldehydes and PAN. Pollutant classes & water quality Primary pollutants are emitted directly (CO, SO2, NO, particulates); secondary pollutants form in the air (O3, H2SO4, PAN). Water quality is judged by BOD (biochemical oxygen demand—oxygen microbes need to degrade organics; high BOD = polluted) and COD. Eutrophication is nutrient over-enrichment causing algal blooms and oxygen depletion. The stratospheric ozone layer shields us from UV; it is maintained by the Chapman cycle and destroyed catalytically by chlorine radicals—one Cl atom can destroy thousands of O3 molecules. Green

HSC 2027 Science — Teacher’s Guide 93 NO2 hν −−→NO + O, O + O2 −→O3, 2C + O2 −→2CO, CO2 + H2O −→H2CO3 (d) Gas data: Vm = 22.4 L mol−1 (STP); PV = nRT; Dalton P = P pi; ppm by volume = Vi Vtotal × 106. 30.3 Tables, Diagrams & Visual Layouts Pollutant Source Effect CO2 combustion greenhouse warming SO2 coal, smelting acid rain, lung damage NOx vehicles, lightning acid rain, smog CO incomplete combustion toxic (binds haemoglobin) CFCs refrigerants, aerosols ozone depletion particulates dust, soot respiratory, haze Earth surface solar IR trapped CO2,CH4 layer Figure 1.1 — Greenhouse gases re-radiate infrared back to the surface. 30.4 Worked Mathematical Problems Worked Problem 30.1 (Molar volume) What volume does 2.2 g of CO2 occupy at STP? (M = 44.) Solution. n = 2.2/44 = 0.05; V = 0.05 × 22.4 = 1.12 L. 1.12 L . Worked Problem 30.2 (Partial pressure) Air at 1 atm is 21% O2 by volume. Find pO2. Solution. pO2 = xO2P = 0.21 × 1 = 0.21 atm. 0.21 atm . Worked Problem 30.3 (Pollutant in ppm) A 1000 L air parcel holds 0.05 L of SO2. Express in ppm. Solution. ppm = 0.05 1000 × 106 = 50 ppm (≫safe ∼0.1 ppm). 50 ppm . Worked Problem 30.4 (Acid-rain stoichiometry) How much H2SO4 forms from 6.4 g