Camosun College Chemistry 253 Exam Notes

A. Definitions

  • Positive feedback: A process where the effects of a small disturbance magnify itself, leading to an increase in disturbance; e.g., melting ice reduces Earth’s albedo, causing further warming and more ice melt.

  • Free Radical: Highly reactive species with unpaired electrons; e.g., hydroxyl radical (·OH) facilitates pollution formation in the atmosphere.

  • DBP (Disinfection Byproducts): Compounds formed when disinfectants like chlorine react with natural organic matter in water; e.g., trihalomethanes (THMs), which can pose health risks.

  • ODP (Ozone Depletion Potential): A measure of a chemical's potential to deplete the ozone layer; e.g., CFCs have a high ODP due to their ability to release chlorine atoms that catalyze ozone destruction.

  • β-emitter: A type of radioactive decay involving the emission of beta particles; e.g., carbon-14 dating uses β-emitters to analyze sediment layers.

  • PCDD (Polychlorinated dibenzodioxins): Toxic compounds formed during combustion processes; e.g., dioxins are linked to various carcinogenic effects.

  • PM2.5 Index: A measure of particulate matter with a diameter of less than 2.5 micrometers; these particles can penetrate the lungs and enter the bloodstream, leading to health issues.

B. Aquatic Chemistry

2. (a) SO2 Concentration Calculation
  • Given: (120 ext{ ppbv} = 0.120 ext{ ppmv})
  • Henry’s law constant: (K_H = 1.82 ext{ mol L}^{-1} ext{ atm}^{-1})
  • Total pressure: (P = 1.055 ext{ atm})
  • Solution concentration:
    [
    C = K_H \cdot P \Rightarrow \ C = 1.82 imes 1.055 = 1.92 ext{ mol L}^{-1}\
    ]
  • Convert to mg/L (using molar mass of SO2 = 64.07 g/mol):
    [
    C_{mg/L} = 1.92 ext{ mol L}^{-1} \cdot 64.07 ext{ g/mol} \cdot 1000 mg/g = 122,000 ext{ mg/L}<br /> ]
2. (b) pH Calculation of Water Droplet
  • Reaction with water: (SO2 + H2O \rightarrow H2SO3)
  • Dissociation:
    [
    H2SO3 \leftrightarrow HSO3^{-} + H3O^{+} \
    K_a1 = 1.72 \times 10^{-2}\
    ]
  • Assume ([HSO3^{-}] \approx [H3O^{+}]), calculate using:
    [
    K_a1 = \frac{[HSO3^{-}][H3O^{+}]}{[H2SO3]} = 1.72 \times 10^{-2} \
    ]
  • pH can be determined from concentration estimates.
3. Alkalinity Calculation from Wastewater Sample
  • Volume of HCl: (13.03 ext{ mL} = 0.01303 ext{ L})
  • Alkalinity (mol ([H^+]/L)):
    [
    [H^+] = C \cdot V = 0.01872 ext{ mol/L} imes 0.01303 ext{ L} = 2.43 imes 10^{-4} ext{ mol/L}<br /> ]
4. PCB Congener and Uses
  • (a) Congener with seven chlorines: 2,2',3,3',4,4',5-heptachlorobiphenyl.
  • (b) Main industrial use: Electrical insulating fluids; (c) Pollutant formation upon heating: Dioxins; of concern due to their high toxicity.

C. Atmospheric Chemistry

9. Pressure and Concentration in Calgary
  • (a) Estimate pressure at altitude: Use barometric formula considering altitude.
  • (b) Concentration of air molecules: Utilize ideal gas law to find (n/V) based on temperature and pressure.
  • (c) NO concentration in downtown: Convert (100 ext{ ppbv}) to molecules cm(^{-3}) using total air concentration.
10. Light and HBr Dissociation
  • (a) Calculate maximum wavelength:
    [
    E = hv = \frac{hc}{\lambda} \Rightarrow \lambda = \frac{hc}{E}\
    ]
  • (b) Photon range of dissociation belongs to UV light; not abundant in lower stratosphere.
12. Titan’s Temperature Calculation
  • (a) Calculate mean surface temperature assuming black body:
    [
    T = (\frac{S(1-A)}{\sigma})^{1/4}\
    ]
  • (b) Wavelength of maximum emissivity calculated using Wien's displacement law.
14. Conditions for Photochemical Smog
  • Severe episodes are common under stagnant atmospheric conditions, high temperatures, and abundant sunlight encouraging high ozone formation.
Miscellaneous Equations

  • General conversions, ideal gas law, and various constants relevant to calculations provided.

  • Important to show full workings and maintain significant figures across calculations with appropriate units.