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midterm_quiz1 - 1.725 Fate and Transport of Chemicals in...

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1.725 Fate and Transport of Chemicals in the Environment Quiz #1 October 21, 2004 1) Sodium ferrocyanide, Na 4 Fe(CN) 6 is routinely added to road salt, typically in the amount of salt kg Fe(CN) Na mol 26 6 4 µ , as an anticaking agent. Despite it's worrisome name, this compound is non-toxic and has even been approved as a food additive. Reports have shown, however, that ferrocyanide in aqueous solution breaks down to form free cyanide (a highly toxic compound) in the presence of sunlight. Fe(CN) 6 4- FeCN + + 5CN - In water CN - is in equilibrium with HCN: HCN = H + + CN - K=10 -9 mol/L a) On a cold day in early November, freezing rain is expected, so the roads are salted. 5 cm of rain falls. The rain washes the salt from the roads, and the runoff (whose pH is 6.9) accumulates in ponds. Given a salt application rate of 0.10 kg salt/m of road, calculate concentration of Na 4 Fe(CN) 6 in highway run-off. Assume road width of 15m. b) What fraction of CN T is present as CN - ? c) As the first step in estimating the risk due to inhalation of air above the puddles of runoff, calculate the initial flux density of HCN volatilizing from a puddle of runoff, given a "piston" velocity of 1 cm/hr, and a puddle depth of 10cm.
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2) The Henry's constant for O 2 at a certain temperature is 540 (L-atm)/mol. Given that the atmosphere is about 1/5 oxygen:
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