Reference no: EM133041872
Question 1. (a) A truck driver carrying a load of lead nitrate (Pb(NO3)2) lost control of his semi-truck after hitting a patch of ice and crashed the truck into Blue Lake, which was right next to the highway. Despite the best efforts of the emergency workers, several of the crates containing lead nitrate were damaged, and the highly soluble compound dissolved immediately. Assuming the lake is initially at circumneutral pH (7), and that the spill resulted the in a total lead concentration of 10-5 M within the lake. Based on the following information, will PbO(s) precipitate out of Blue Lake. Assume all lead nitrate will first dissociate into Pb+2 and NO3- prior to forming lead oxide and lead hydroxides and no other sources of lead exist in the lake.
Lead oxide dissolves via the following reaction
PbO(s) + 2H+ → Pb2+ + H2O
Dissolved lead will form 3 soluble aqueous hydroxides and dissolved lead in water, depending on pH and total lead concentration (Pb(OH)+, Pb(OH)2(eq), Pb(OH)3-. Create a log C pH diagram to solve the problem. For full credit, write and balance the relevant reactions from Ksp to the third hydroxide Ks3 and calculate all reaction K values using appendix A in B@A. The ΔG°r for Pb(OH)3- is -575.7 kJ/mol. Please show your graphical solution for full credit.
Question 2. (a) Due to the geology in the watershed surrounding Blue Lake, the mineral Cotunnite (PbCl2) naturally occurs in the lake (different assumption than problem #1). Before the spill of lead nitrate into Blue Lake, what would the aqueous concentrations of PV and Cl- be in Blue Lake at equilibrium if Cotunnite is the only source of both Pb or Cl- Consider the following
(b) After the spill, assuming the same aqueous concentration of lead in problem 1, what would be the concentration of Cl- in Blue Lake. Compare the Cl- concentrations from before and after the spill and explain the observed behavior.
Question 3. The dissolved Pb (II) in the lake after the spill can react with oxygen, to form Pb (IV). Using the following half reactions, what are Log K, Pe°, Pe°7, E° and E°7 for the overall oxidation of Pb (II) to Pb(IV).
Pb4+ + 2e- = Pb2+
O2(aq) + 4H+ + 4e- = 2H20
Based on how you have combined these reaction which direction will the overall reaction proceed?
Question 4. Residents around the lake are worried about the lead in the lake and want to develop a treatment plan to remove as much lead as possible. Fortunately, a new experimental ion exchange resin has been developed which is extremely effective at removing only Pb" from water. Because of some good connections, the residents can purchase oxalic acid for much cheaper than strong acid. Oxalic acid is added to the lake resulting in a total acid concentration of 900.3 mg/L. Calculate the concentration of Pb2+ in the late after this system reaches equilibrium algebraically. For this problem assume that there is only water and oxalic acid in the lake (no other buffers or species of any kind). Hint, you have enough information in the entire exam to find this solution. Show checks to all assumptions you needed to solve this problem.