8.3 Practice Problems#
If \(K_H\) is \(\pu{29.51 atm L mol-1}\) for \(\ce{CO2}\) and the atmospheric \(\ce{CO2}\) concentration is \(\pu{0.004 atm}\), what is \(\ce{CO2}\) concentration in water at equilibrium?
m-Xylene enters the groundwater system. The average concentration of m-Xylene in the groundwater is \(\pu{100 mg L-1}\). If the groundwater at the top of the saturated zone is in equilibrium with air, calculate the concentration of m-Xylene in the air in \(\pu{mol L-1}\). \(K_H\) for m-Xylene is \(0.43736\). Answer: \(\pu{4.12e-4 mol L-1}\)
It was determined that the adsorption of toluene onto sedimentary particles followed a linear relationship, with \(K_d\) = \(\pu{9.9 L kg−1}\). If the toluene concentration in the groundwater is \(\pu{4.5 mg L−1}\), calculate the concentration of toluene sorbed onto the sedimentary particles in the aquifer. Answer: \(\pu{446 mg kg−1}\)
The first-order rate constant for the breakdown of toluene under aerobic conditions was \(\pu{−0.54 d-1}\); under anaerobic conditions, the rate constant was \(\pu{−0.002 d-1}\). Calculate the time required to degrade \(\pu{90 \%}\) of the toluene under aerobic and anaerobic conditions. Answer: \(\pu{2.7 d}\) and \(\pu{1151 d}\)
Assume an organic contaminant is introduced into an aquifer. Right after the spill, the concentration of the organic contaminant is \(\pu{12 mg L−1}\). A measurement made \(\pu{20 d}\) later reveals that the concentration of the contaminant has decreased to \(\pu{1 mg L−1}\). Assuming that this is a first-order reaction, what is the half-life for this particular organic contaminant? Answer: \(\pu{5.6 d}\)
Lindane (a commonly used pesticide) is considered a persistent organic pollutant (POP) in the environment. It has \(\log K_H = 3.94\) and \(\log K_{ow} = 3.78\), and first-order rate constants for its loss from air, water, and soil/sediment are \(\pu{0.1 d-1}\), \(\pu{0.01 d-1}\), and \(\pu{0.0006 d-1}\), respectively. Estimate the half-life of lindane loss from air, water, and soil/sediment.
In a particular system, the half-life of Lindane undergoing aerobic decomposition is \(\pu{210 d}\). Determine the duration needed for \(\pu{90 \%}\) of the Lindane to break down. Answer: \(\pu{698 d}\)