Environmental Chemistry

ENV440 - Examination 2 (100 points)

Chemistry 440--Environmental Chemistry

Examination 2, 100, points April 2, 2002

Name_________________________

1. (10 points) Write the correct definition, as it applies to environmental chemistry, for each of the following terms:

a. Biochemical Oxygen Demand (BOD)

b. Hydrophobic colloid

c. Nitrogen Fixation

d. Hydrophyllic colloid

e. Zero Point Charge

2. (10 points) Calculate the concentration of methane, CH4, in water at a temperature of 25 ?C if air in equilibrium with this water contains 0.015 atm of CH4. Express your answer in both moles per liter and milligrams per liter (the molecular mass of methane is 16.0g/mol.) The Henry’s Law constant for methane at 25 ?C is 1.34 X 10-3 mol/L-atm.

3. (10 points) Calculate the concentration of methane in the above aqueous solution if the temperature of the water were lowered from 25 ?C to 15 ?C. The heat of solution, ?H, for methane is -3970 cal/mol and R = 1.98 cal/mol-K

4. (10 points) A sediment sample of clay was equilibrated with ammonium ion (NH4+). The ammonium ion was then displaced with Na+. The total amount of ammonium that had been adsorbed by the sediment sample was 55.8 milliequivalents (meq) and the sample had a dried mass of 82.4 g. Calculate the cation exchange capaciticy (CEC) in meq/100g.

5. (8 points) Predict the relative ease of degradation of the following water pollutants by writing a 1 near the most easily degraded substance, a 2 near the second most easily degraded substance, etc.

6. (12 points) Correctly classify each of the following water pollutants according to the following scheme of possibilities: (a) inorganic chemical, nutrient; (b) inorganic chemical, heavy metal; (c) inorganic chemical, radionuclide; (d) organic chemical, chlorinated hydrocarbon; (e) organic chemical; pesticide or herbicide; (f) physical, sediment; (g) physical, thermal; (h) biological, oxygen depleting substance; (i) biological, pathogen:

Water pollutant Classification

NO3- ___________________________

U ___________________________

Dioxin ___________________________

sewage ___________________________

Cd ___________________________

TCE ___________________________

7. (20 points) Predict the correct products in each of the following chemical reactions:

 
A =

B =

C =

D =

E =

8. (8 points) Describe the two ways organic carbon is removed from sewage water, and give the balanced equations for aerobic and anaerobic degradation of biomass.

9. (8 points) Describe where heavy metals (i.e., Mn2+, Pb2+ and Cd2+) are removed from sewage water in an activated sludge wastewater treatment plant (both in the secondary and tertiary stages), and give a balanced chemical reaction for lead removal in the tertiary stage.

10. (4 points) What is the objection to using chlorine gas to disinfect wastewater effluent, and suggest two alternative substances that can be uses without causing this problem.

Environmental Chemistry -- ENV 440
Last Updated:  03/22/2003