MChem Master of Chemistry Environmental Chemistry 2 — Questions and Answers
Question 1: In the context of soil contamination, what does the Koc value measure?
- The rate of microbial degradation of a compound
- The organic carbon-normalized partition coefficient between soil and water (Correct answer)
- The volatility of a pollutant from soil
- The toxicity of a compound to soil organisms
Correct answer: The organic carbon-normalized partition coefficient between soil and water
Koc is the organic carbon-normalized partition coefficient, indicating how strongly a hydrophobic organic pollutant adsorbs to soil organic matter relative to pore water.
Question 2: What is the main mechanism of stratospheric ozone depletion by chlorofluorocarbons (CFCs)?
- CFCs absorb UV radiation and block it from reaching the stratosphere
- Cl• radicals from photolysis of CFCs catalytically destroy O3 (Correct answer)
- CFCs react directly with O2 to form ClO3
- CFCs raise stratospheric temperatures, slowing ozone production
Correct answer: Cl• radicals from photolysis of CFCs catalytically destroy O3
UV photolysis of CFCs releases Cl• radicals in the stratosphere, which catalytically destroy ozone via Cl• + O3 → ClO + O2 cycles.
Question 3: Which type of chemical weathering converts feldspar minerals in rocks to clay minerals through reaction with carbonic acid?
- Oxidation
- Hydrolysis (Correct answer)
- Dissolution
- Carbonation
Correct answer: Hydrolysis
Hydrolysis of feldspars by weakly acidic water (containing dissolved CO2) produces clay minerals (e.g., kaolinite) and releases ions to solution.
Question 4: What is the significance of the octanol-water partition coefficient (Kow) for environmental fate of organic pollutants?
- It predicts the rate of photodegradation in surface waters
- It predicts bioaccumulation potential and hydrophobicity (Correct answer)
- It measures the rate of volatilization from soil
- It determines the pH buffering capacity of the compound
Correct answer: It predicts bioaccumulation potential and hydrophobicity
A high logKow indicates a compound is lipophilic, predicting strong bioaccumulation in fatty tissues and partitioning into organic matter.
Question 5: Which chemical species is primarily responsible for acid rain formation from sulfur dioxide emissions?
- SO2 dissolves directly in rain as H2SO3 with no further reaction
- SO2 is oxidized to SO3 then hydrated to H2SO4 (Correct answer)
- SO2 reacts with NO2 to form HONO
- SO2 reacts with O3 to form SO4•−
Correct answer: SO2 is oxidized to SO3 then hydrated to H2SO4
SO2 is oxidized (in the gas phase by •OH or in droplets by H2O2/O3) to SO3, which reacts with water to form sulfuric acid (H2SO4) — the main acid rain component.
Question 6: What is the 'critical load' concept used for in environmental chemistry?
- Maximum contaminant level permitted in drinking water under the Safe Drinking Water Act
- The threshold deposition of acidifying pollutants below which significant ecosystem damage does not occur (Correct answer)
- The carrying capacity of a river system for dissolved oxygen
- The maximum soil concentration before phytotoxicity occurs
Correct answer: The threshold deposition of acidifying pollutants below which significant ecosystem damage does not occur
Critical load is the quantitative estimate of pollutant deposition below which significant harmful ecological effects do not occur according to current knowledge.
MChem Master of Chemistry Environmental Chemistry 2
In the context of soil contamination, what does the Koc value measure?