a. You are tasked with deciding how to remediate a site where the groundwater ha
ID: 887652 • Letter: A
Question
a. You are tasked with deciding how to remediate a site where the groundwater has beencontaminated with trichloroethylene (TCE). If conditions are right, the growth of certain groupsof naturally occurring bacteria can be stimulated, and these bacteria will dechlorinate the TCE allthe way to chloride and ethene: 3H2 + HC2Cl3 -> C2H4 + 3Cl- + 3H+
To determine whether this reaction could proceed at this contaminated site, you measure theconcentrations of the above components and find them to be: pH = 8.1, [Cl-] = 3 mg/L, [H2] =5x10-10 M, [HC2Cl3] = 3.8 mM, [C2H4] = 3.8 microM, I = 0.007 M. Would you conclude that
dechlorination of TCE to ethene was thermodynamically possible at this site? For simplicity,assume a temperature of 25oC.
b. The reductive dechlorination of TCE occurs in three steps, the last of which is the reductionof vinyl chloride (H3C2Cl) to ethene. Because vinyl chloride is carcinogenic, the build-up of thisintermediate is highly undesirable. Given the concentrations listed above and a vinyl chlorideconcentration of 0.01 mg/L, could the reduction of vinyl chloride occur under the existingconditions?
Explanation / Answer
Dechlorination of TCE is thermodynamically possible because concentration of all the species is thermodynamically possible at 25 degreeC and the reduction of TCE to ethene willl be possible
Reduction of vinyl chloride will occur but at very less amount so there is a possibility that TCE is remaining and conversion to Ethene will be very less
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