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Hour Exam #4

Hour Exam #4. Review. Polycyclic Aromatic Hydrocarbons (PAHs) are ubiquitous and produced in the US in an excess of 8500 tons annually. What is the primarily health concern regarding PAHs and list three sources of PAHs to which people are exposed.

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Hour Exam #4

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  1. Hour Exam #4 Review

  2. Polycyclic Aromatic Hydrocarbons (PAHs) are ubiquitous and produced in the US in an excess of 8500 tons annually. What is the primarily health concern regarding PAHs and list three sources of PAHs to which people are exposed. • The primary health concern is cancer. Three sources for exposure include food, soot, and smoke.

  3. Cite the results of one study discussed in class that would support the proposition that some anthropogenic compounds are acting as potential “endocrine disrupters.” • There were several studies discussed in class including injecting roosters to DDT, Lake spill at Lake Apopka in Florida, TBT and dog welks,

  4. The figure on the left shows the dissolved oxygen levels in the Cape Fear River for three different dates: (a) Explain why the dissolved oxygen level goes through a “sag.” (b) explain why the August values are below October values, and (c) Explain why there is a state policy not to allow additional plants where their discharges on the Cape Fear River would further reduce the dissolved oxygen levels. (a) The system goes through a “sag” because there are two processes occuring – Deoxygenation and reaeration.(b) August values are below October because with the colder temperatures there is more oxygen in the water.(c ) Do not want more oxygen depletion because 5 ppm is considered deleterious to aquatic life, and the Cape Fear is dangerously close.

  5. Given the following information,. • H2CO3 H+ + HCO3- Ka1 = 4.5x10-7 • HCO3- H+ + CO32- Ka2 = 4.7x10-11 • CaCO3 Ca2+ + CO32- Ksp = 4.6x10-9 • H2O  H+ + OH- KW = 1.0x10-14 • (a) Calculate the pH of a 0.10M solution of Na2CO3 (Remember sodium carbonate, Na2CO3, is 100% soluble). • CO32- +H2O > HCO3- + OH- • 0.10 --- ---- • 0.10 – x x x • X2/0.10 = KW/Ka2 = 1x10-14/4.7x10-11 = 2.1x10-4 • X2 = 2.1x10-5 x = 4.58x10-3 pOH = 2.33 pH = 11.7

  6. Determine the equilibrium constant for the following reaction. • HCO3- + Ca2+ CaCO3(s) + H+ • HCO3- H+ + CO32- Ka2 = 4.7x10-11 • CaCO3 Ca2+ + CO32- Ksp = 4.6x10-9 • H2O  H+ + OH- KW = 1.0x10-14 • HCO3- H+ + CO32- Ka2 = 4.7x10-11 • Ca2+ + CO32- CaCO3 K = 1/Ksp =2.1x108 • K = 2.1x108 x 4.7x10-11 =9.87x10-3

  7. Explain Henry’s Law and illustrate with an application. • Henry’s Law says the concentration of a soluble gas in a liquid is directly proportional to the pressure of the gas, e.g. • X(CO2(l)) = KHPCO2 An illustration of Henry’s Law is the solubility of oxygen at ambient temperature where the concentration of oxygen molecules is 8.7 ppm or 8.7 mg/L. • Explain LeChatelier’s Principle and illustrate with an application. • LeChatelier’s Principle states that if a system is at equilibrium and a stress is placed on the system, the system will respond to alleviate the stress. An example would be an exothermic reaction, where if the temperature of the system is increased, the reaction will respond to decrease the concentration of the products and increase the concentration of the reactants.

  8. In class we discussed the political issues related to the use of MTBE additive to gasoline. Explain (a) Why MTBE has been added to gasoline, (b) why is there a concern about MTBE, and (c) how has this concern influenced the delay in passage of the Energy Bill. (a) MTBE was added to gasoline in response to the Clean Air Act to increase the oxygen content resulting in cleaner burning and less pollutants causing photochemical smog, e.g. CO and ozone. (b) The concern about MTBE is that it might get into the water column, particularly in aquifers, resulting in the water not being drinkable. (c ) This concern caused the oil companies to lobby for a safe harbor, or a limitation on liability from law suits on contaminated water supplies. Currently there is a “safe harbor” but with the recent elections the prognosis is uncertain.

  9. You have found that your drinking water contains malathion, an organophosphate pesticide, and a high concentration of nitrate. (a) Will the addition of a carbon filter on your water tap remove these contaminants? Why or why not? Other than using a carbon filter, how could you make the water safe to drink? • The carbon filter should remove the organic pesticide from the water, but not the nitrate. Charcoal or carbon will absorb organic compounds, but the nitrate will pass through. • To make it safe to drink, you could distill the water, this will remove both the contaminants. Or, as discussed in class, you could use an ion-exchanger or dilute the tap water with nitrogen free water to place the concentration of nitrate to an acceptable level.

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