Question

Hydrogen sulfide (H₂S) is a problem in sewage because it can be oxidized to form sulfuric acid and corrode pipes and because hydrogen sulfide gas produces an unpleasant odor (rotten egg smell). A team of engineers in Denver (total atmospheric pressure 0.92 atm) is worried about the hydrogen sulfide concentrations in a sewage system. They take a sample of air in the empty space of a partially filled sewage pipe and measure a H₂S concentration of 313 ppm by volume and a temperature of 10 °C.

1. What is the concentration of dissolved H₂S in the sewage in mg/L?
2. The engineers want to reduce the odor of the sewage, so they decide to reduce the concentration using a precipitation reaction. They first need to adjust the pH of the sewage to convert H₂S to the sulfide ion (S^2-). Then, they need to add iron (Fe) to precipitate solid FeS. At what pH would 90% of the total sulfide concentration (C_T) be in the S^2- form?
   1. 4.5
   2. 7.2
   3. 11.9
   4. 12.8
3. Assume that the pH has been adjusted so that 90% of C_T is in the S^2- form. If C_T is 5 x 10^-15 mol/L, what is the minimum Fe concentration (mg/L) the engineers should add to start precipitating FeS?

Answer 1

Kind refer to the attached images