Lecture 82/07/05 Seminar: Monday 2/7 4:30 Room 006 Eric Howe “Untangling sickle-cell anemia and the discovery of heterozygote protection to address students’ misconceptions in genetics”

Problem 78 If the concentration of Mg 2+ ion in sea water is 1350 mg/L, what OH - concentration is required to precipitate Mg(OH) 2 ? K sp (from appendix J) = 5.6 x

Separations Using the solubility rules, how could you separate the following ion pairs? 1. Na + and Ba Pb 2+ and Ca 2+

Separations Each of the following pair of ions is found together in aqueous solution. Using the table of solubility product constants in Appendix J, devise a way to separate these ions by adding one reagent to precipitate one of them as an insoluble salt and leave the other in solution. Cu 2+ and Ag +

Cu +, Cu 2+ CuBr 6.3 x CuI 1.3 x Cu(OH) x CuSCN 6.3 x Ag + AgBr 5.4 x AgBrO x AgCH 3 CO x AgCN 6.0 x Ag 2 CO x Ag 2 C 2 O x AgCl 1.8 x Ag 2 CrO x AgI 8.5 x AgSCN 1.0 x Ag 2 SO x 10 -5

If HCl is added slowly to a solution that is 0.10 M Pb 2+ and 0.01 M Ag +. K sp (AgCl) = 1.6 x K sp (PbCl 2 ) = 2.4 x Which precipitates first AgCl or PbCl 2 ? Can you separate the two ions by precipitation?

Which precipitates first AgCl or PbCl 2 ? Smaller [Cl - ] to precipitate  first to precipitate Silver precipitates first

Can you separate the two ions by precipitation? Since silver precipitates first, need to see if you can precipitate all of the silver before any of lead is precipitated Remember that [Cl - ] = M when Q=K for PbCl 2 so as long as [Cl - ] < M  Q < K and no precipitation Check [Ag + ] at [Cl - ] = M K sp = [Ag + ][Cl - ] 1.6 x M = (x)(0.049) x = [Ag + ] = 3.3 x M All the silver essentially removed  good separation

Common Ion Effect BaSO 4 (s) ↔ Ba 2+ (aq) + SO 4 2- (aq) If you add Na 2 SO 4 to the solution [SO 4 2- ] increases Reaction shifts to the left Solubility of BaSO 4 decreases

Quiz 3 – 1/31/04 1. Given the following reaction: O 2 (g) + N 2 (g) ⇄ 2NO (g) If K p = 0.05 at 2200 o C and P O2 = 0.21 atm and P N2 = 0.79 atm, what are the equilibrium concentrations of the three gases? 2. Which direction will the following equilibria shift if the volume is reduced? 2 SO 2 (g) + O 2 (g) ⇄ 2 SO 3 (g)