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This is an important problem because nitrogen, in the form of ammonium ions, degrades water quality by promoting algal growth and needs to be removed (or at least minimized). a) One way to remove nitrogen during wastewater treatment is to “blow off” less soluble ammonia gas by constantly blowing clean air through a tower while spraying in contaminated water. How would you expect such a water treatment process to scale with pH (at constant temperature)? ANS: Starting with the simplified equilibrium reaction for aqueous ammonis& .. NH3(g) + H2O(liq) ð ð ð ð ðÛð ð ð ð[ðNðHð4ðOðHð]ð ð ð ð ðÛð ð ð ð ðNH4+(aq) + OH-(aq) Therefore, if [OH-] increases, equilibrium shifts left, and the solubility of NH3 decreases. Otr to put the words in context with the question, raising the pH favors removal of nitrogen by “blowing off” ammonia. b) If the pH of a sample of farm runoff waste water is 9, what is the fraction of the nitrogen in the waste water that is in the ammonia form and can therefore be “blown off?” ANS: 0.36 2. Lead in the environment is a particular issue, but especially where acid run-off comes in contact with mine tailings containing insoluble lead salts. For example, lead sulfate is made soluble by acid according to the following reactions: PbSO4(s) ð ð ðÛð ð ð ð ð Pb2+(aq) + SO42-(aq) SO42-(aq) + H3O+(aq) ð ð ðÛð ð ð ð ð HSO4-(aq) + H2O(liq) b) Write the overall (net) reaction and determine the value of the equilibrium constant, given the following data: Ksp(PbSO4) = 1.3 .. 10-8 Ka(H2SO4) = 1 .. 105 Ka (HSO4-) = 1.3 .. 10-2 b) Determine the solubility of lead sulfate in run-off that tests at pH 1. c) Compare the value in (b) to the solubility in pure water. 3. Determine the relative pH values of 0.1 M aqueous solutions of ammonium cyanide (NH4CN), ammonium acetate (NH4OAC), and ammonium hydrogen sulfide (NH4HSO4)…. assuming the ammonium salts are all soluble…. and briefly explain your answer. 4. Offer a brief explanation for each of the following: Adding conc. HCl to a saturated solution of NaCl results the immediate formation of an insoluble white substance. On adding 50. mL of 0.10 M barium hydroxide solution to 50. mL of 0.10 M sulfuric acid solution, the original solution is no longer conducting. The last traces of color disappear from a tube filled with a mixture of (colorless) dinitrogen tetroxide and (red) nitrogen dioxide at the temperature of ”dry ice.” Soluble zinc and aluminium salts have similar chemistries in aqueous solutions. For example, both produce gelatinous hydroxides (on addition of base) that dillove in excess base, and in acid. Glacial acetic acid becomes conducting on dilution with water. Chloroacetic acid is a weaker acid than fluoroacetic acid, but stronger than acetic acid. 5. Answer each of the following as indicated and provide a brief explanation: Using only the data in the following graph, one must conclude that the reaction being described is (exothermic, endothermic). Using only the data in the following graph, one must conclude that Dn for the reaction being described is (less than, equal to, greater than) zero. For the reaction C(s) + CO2(g) ð ð ðÛð ð ð 2 CO(g) Write a general expression for Kp and another for Kc in terms of Kp. 6. Would you expect the equilibrium constant for the reaction H2(g) ð ð ðÛð ð ð 2H(g) to (increase, decrease, remain unchanged) with increasing temperature? Briefly explain! 7. Ammonia and carbon dioxide are formed as the only products as solid ammonium carbamate dissociates at 25°C according to the following reaction: NH4COONH2(s) ð ð ðÛð ð ð ð ð ð ð ð ð ð ð ð2NH3(g) + CO2(g) If the total pressure of the gases at equilibrium is 0.116 atm, then what must be the equilibrium constant Kp for the reaction at that temperature? If 0.1 atm of CO2 is introduced after equilibrium has been achieved, will the final pressure of CO2 be (greater, the same, less than) 0.1 atm? Will the pressure of NH3 (increase, stay the same, decrease)? 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