Final Exam

Environmental Chemistry

ENV440 - Final Exam (100 points)

If your cow sounds like this If your cow sounds like this

then fire up the barbecue. may we suggest fish.

Chemistry 440--Environmental Chemistry

Final Examination, 150 points Name_________________________

1. (20 points) Write the correct definition, as it applies to environmental chemistry, for each of the following terms:

a. Troposphere

b. Aerosol

c. Environmental chemistry

d. Chlorofluorocarbons

e. Pollutant

f. Denitrification

g. Macronutrients in soil

h. Hazardous waste

i. Algae

j. Tertiary waste treatment

2. (12 points) Write balanced nuclear reactions for the formation of helium-4 from hydrogen-1 (the reaction that fuels our sun). There are three individual reactions and one overall reaction for hydrogen burning.

3. (12 points) The element platinum is reduced by iron. Magnesium is not reduced by iron and forms an oxide complex. Silver is not reduced by iron and forms a sulfide complex. Classify each of these elements according the Goldschmidt classification scheme (siderophile, lithophile, chalcophile or atmophile) and state where each element would be concentrated (core, crust or atmosphere) in a newly formed planet.

Element	Goldschmidt Classification	Location in new planet
platinum
magnesium
silver

4. The total alkalinity of a natural water sample is measured by titration and found to contain 2 x 10^-3 alkalinity equivalents ( total alkalinity = [HCO₃^-] + 2[CO₃^2-] + [OH^-] - [H⁺]. The pH of this water sample is 10.0. Use this information to calculate answers to the following questions.

a. (10 points) What percent of the total alkalinity is due to presence of the bicarbonate ion (HCO₃^-)?

b. (5 points) Calculate the actual concentration of hydroxide ion, [OH^-], under these conditions:

5. (10 points) A natural water sample contains 5 x 10^-4 M total nitrogen concentration, which may be present in the forms NO₃^-, NO₂^- and NH₄⁺. Calculate the pE for this water sample when the ratio of nitrate to nitrite is 50% NO₃^- and 50% NO₂^-. Assume that the pH of this water sample is 7.0.

6. Given below is the pE/pH diagram for iron (total iron concentration = 1 x 10^-3 M) in an aqueous solution that contains 1 x 10^-5 M carbonate ion. Use this information to answer the following questions.

a) (4 points) What is the predominate form of iron at pE = +5 and pH = 3?

b) (4 points) What is the predominate form of iron at pE = +5 and pH = 8?

c) (4 points) What is the predominate form of iron at pE = +15 and pH = 3?

7. (10 points) Calculate the concentration of carbon dioxide, CO₂, in water at a temperature of 25 ° C if air in equilibrium with this water contains 0.005 atm of CO₂. Express your answer in both moles per liter and milligrams per liter (the molecular mass of carbon dioxide is 44.0g/mol. The Henry’s Law constant for carbon dioxide at 25 ° C is 3.38 X 10^-2 mol/L-atm.

8. (10 points) Calculate the intrinsic solubility for calcium carbonate, CaCO₃, in an aqueous salt solution with an ionic strength of 0.050 and a temperature of at 25 ° C. K_sp = 4.8 X 10^-9. The activity coefficients, at 0.050 ionic strength and 25 ° C, for Ca²⁺ and CO₃^2- are:

g ( Ca²⁺) = 0.485; g ( CO₃^2-) = 0.455

9. (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.

10. (10 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

PO₄^-3___________________________

Hg ___________________________

DDT ___________________________

Fecal coliform ___________________________

Pb ___________________________

11. (6 points) List the two equations that show how chlorine atoms (or nitrogen oxide or chlorine oxide) react with ozone to form diatomic oxygen. Give the net, overall, reaction for this process.

12. (5 points) Use the generalized reaction mechanism of photochemical smog formation to explain why aldehydes start at a very low concentration, build up in concentration until about 2:00 p.m. in the afternoon, and then decrease to their original concentrations?

13. (10 points) Sketch a diagram of the "rock cycle," label the sedimentary, metamorphic and igneous rocks, and show how these three rock types are related to each other.

(10 points) Match the following:

1. Metamorphic rock	(a) Produced by the precipitation or coagulation of dissolved or colloidal weathering products.
2. Chemical sedimentary rocks	(b) Weathered parent rocks from which the soil originated.
3. Organic sedimentary rocks	© Largest particle size fraction (2-60 mm) according to the United Classification System.
4. Topsoil	(d) Contain residues of plant and animal remains.
5. C horizon	(e) Layer of maximum biological activity in soil that contains most of the soil organic matter.
	(f) Formed from action of heat and pressure on sedimentary or igneous rock.