1. Friday, April 5 Work on review problems –solubility Work in groups of 3 on review problems Come up and write answer on board when you think you have the correct answer

2. Calculate the molar solubility of Left sideRight side Top of room Ag 3 PO 4 K sp = 2.6 x 10 -18 Al(OH) 3 K sp = 3.0 x 10 -34 Bottom of room PbCl 2 K sp = 1.7 x 10 -5 Ag 2 CrO 4 K sp = 2.6 x 10 -12 When done Send someone to board Put up answer and equation used to get there

3. Molar Solubility Answers Ag 3 PO 4 ; x = 1.8 x 10 -5 M Al(OH) 3 ; x = 1.0 x 10 -9 M PbCl 2 ; x = 1.6 x 10 -2 M Ag 2 CrO 4 ; x = 8.7 x 10 -5 M

4. Solubility continued The magnesium and calcium ions present in seawater ([Mg 2+ ] = 0.059 M and [Ca 2+ ] = 0.011 M) can be separated by selective precipitation with KOH. Calculate the [OH - ] that would separate the metal ions. K sp of Mg(OH) 2 = 6.3 x 10 -10 ; K sp of Ca(OH) 2 = 6.5 x 10 -6 Ans: [OH - ]: 1.03 x 10 -4 M

5. LEFT side: The water solubility of SrF 2 is 0.011 g/ 100 mL. Calculate the solubility product constant. K sp = 2 x 10 -9 RIGHT side: The water solubility of Ag 2 S is 3.12 x 10 -15 g/ 100 mL. Calculate the solubility product constant. K sp = 8 x 10 -48 Solubility questions

6. Conceptual solubility question Explain how the molar solubility of CaF 2 will differ in a solution containing 0.100 M NaF compared to in a solution of pure water? Common ion effect Molar solubility of CaF 2 in NaF is lower than in pure water.

7. Buffer questions Calculate the pH of a buffer that consists of 0.45 M of C 6 H 5 COOH and 0.25 M of C 6 H 5 COONa. K a = 6.3 x 10 -5. Ans: pH = 3.94

8. Now assume that the pH increased to 5.10, what are the concentrations of the buffer components? i.e.) [C 6 H 5 COOH], [C 6 H 5 COONa]? Ans: [A] = 0.078 M; [B] = 0.622 M Check: Does this make sense? Yes, an increase in pH means we have more base in solution. Buffer questions

9. Find the pH of a buffer that consists of 0.25 M NH 3 and 0.15 M NH 4 Cl (p ­ K b of NH 3 = 4.75). Approach: First find pK a. Then sub pK a into Henderson Hasselbalch equation. Ans: pH = 9.47 Buffer questions

10. What is the ratio of [Pr - ]/ [HPr] buffer that has a pH of 5.44 (K a of HPr = 1.3 x 10 -5 )? Ans: [Pr - ]/[HPr] = 3.55 This means need ~3.6 times more [Pr - ] than [HPr] to get to pH of 5.44. More Buffer questions

11. Last Buffer question A buffer containing 0.2000 M of acid, HA, and 0.1500 M of its conjugate base, A -, has pH of 3.35. What is the pH after 0.0015 mol of NaOH is added to 0.5000 L of this solution? Approach: First find pK a. Set up equation showing the neutralization reaction with ICE table. Use Henderson Hasselbalch equation to solve for pH. Ans: pH = 3.37 Last Buffer Question