Examination 1, 100 points Name_________________________

February 20, 2002

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

a. Contaminant

b. Environmental Chemistry

c. Biosphere

d. Hazardous Waste

e. Hydrosphere

2. (8 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) A wooden stick figure was found in a cave, along with pottery shards and other artifacts. The cave is located in a remote part of the Grand Canyon, near a permanent freshwater spring. The C-14 activity of the stick figure was 8.6 disintegrations per minute per gram of carbon. Living tissue has a C-14 activity of 15.3 disintegrations per minute per gram of carbon. How many years ago was the dwelling inhabited? The half-life for C-14 is 5700 years.

4. (12 points) The elements nickel, gold and platinum are reduced by iron. Barium, magnesium and sodium are not reduced by iron and form strong oxide complexes. Silver is not reduced by iron and forms a strong 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
nickel
silver
nirtrogen
barium
magnesium
platinum

5. (6 points) How did the composition of the earth’s early atmosphere (4.5 billion yrs. bp) differ from the modern atmosphere. Illustrate your answer with the examples for the predominate form of carbon, nitrogen and sulfur in the early atmosphere and the modern atmosphere.








The following questions require calculation of a numerical answer using equations that were discussed in lecture and included in homework problems. Formulas, equations and the values of equilibrium constants, ones that will be useful in solving these problems, are provided at the end of the examination.

6. The total alkalinity of a natural water sample is measured by titration and found to contain 1.0 x 10^-3 alkalinity equivalents ( total alkalinity = [HCO₃^-] + 2[CO₃^2-] + [OH^-] - [H⁺¹]). The pH of this water sample is 10.4. Use this information to calculate answers to the following questions.

a. (10 points) What percent of the carbonate present is in the form of the carbonate ion (CO₃^2-) at pH = 10.4?












6b. (10 points) What is the molar concentration of carbonate ion (CO₃^2-) in this sample?












6c. (10 points) What would be the concentration of calcium ion if this sample was in a saline solution (ionic strength = 0.100) in equilibrium with solid calcium carbonate (and not exposed to air)? γCa²⁺ = 0.405, γ(CO₃^2-)- = 0.370





7. (12 points) A natural water sample contains 1 x 10^-4 M total sulfur concentration, present in the forms SO₄^2-, H₂S, HS^-, and S(s). Use the half reaction for reduction of sulfate (SO₄^2-) to elemental sulfur S(s) to derive an equation for the line that would separate sulfate from elemental sulfur in the pE/pH diagram for sulfur in water.












8. (10 points) Use the pE/pH diagram shown below to answer the following questions.

What is the predominant form of cobalt at a pE of 7.0 and a pH of 4.0?

What is the predominant form of cobalt at a pE of 7.0 and a pH of 10.0?

What is the predominant form of cobalt at a pE of 2.0 and a pH of 9.0?

What is the predominant form of cobalt at a pE of -3.5 and a pH of 5.5?

List the forms of cobalt that would be transported in water: