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16.6 Solubility Equilibria

16.6 Solubility Equilibria. Solubility Equilbria. Many ionic cmpds are very soluble in water (as NaCl) but others have limited solubility--p 109 table 4.2.

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16.6 Solubility Equilibria

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  1. 16.6 Solubility Equilibria

  2. Solubility Equilbria • Many ionic cmpds are very soluble in water (as NaCl) but others have limited solubility--p 109 table 4.2

  3. Let’s envision what happens when make a saturated solution of some ionic cmpd of limited solubility, as CaCO3. Assume that the solvent is water and the temp is 25oC. • CaCO3(s)  Ca2+(aq) + CO32-(aq)  CaCO3(aq) • A certain quantity of CaCO3 goes into solution and immediately dissociates into ions. _______________

  4. A saturated solution has ___________ • Remember in writing equil expressions that pure solids, pure liquids--______.

  5. Solubility Product • CaCO3(s)  Ca2+(aq) + CO32-(aq) • Ksp = _____________ • Ksp is called the _______________ (equil constant) (Implies ideal behavior) • [Ca2+] implies conc units in _________ • Ksp values tabulated in book, p 672, table 16.2

  6. Relationship btn molar sol’y (s) and Ksp • Define molar solubility, s ,as the ________ • Let us examine the stoichiometrically different salts and their relationship to molar solubility.

  7. 1:1 salt as AgCl, CaCO3 • AgCl(s)  Ag+(aq) + Cl-(aq) • Ksp = ____________ • [Ag+] = [Cl-] = ____

  8. 2:1 or 1:2 salt as CaF2 or Ag2SO4 • CaF2(s)  • Ksp = ________ • [F-] = __ [Ca2+] = __

  9. 1:3 or 3:1 salt as Fe(OH)3 or Ag3PO4 • Ag3PO4(s) • Ksp = • [Ag+] = ___ [PO43-]= ___

  10. 2:3 or 3:2 salt as Bi2S3 or Ca3(PO4)2 • Bi2S3(s)  • Ksp = • [Bi3+] = ___ [S2-] = _____ • Remember this assumes ideal behavior (as complete ionization--no ion pair formation, no hydrolysis of ions as Al3+ )

  11. Ksp and Q (ion-product) • Remember Ksp refers to a saturated sol’d, Q refers to any sol’n, not just an equilibrium system. • Ag3PO4(s)3Ag+(aq) + PO43-(aq) • Ksp = [Ag+]3[PO43-] • Q = [Ag+]3[PO43-] : these need not be equil concs

  12. If • Q < Ksp ______ • Q = Ksp ______ • Q > Ksp _______

  13. Problems: Ksp to s and s to Ksp • What are the molar solubilities of CaCO3(Ksp = 8.7 x 10-9) and Ag2CO3 (Ksp = 8.1 x 10-12) • Calc Ksp of Ag3PO4, given the sol’y of Ag3PO4 is 6.7 x 10-3 g/L

  14. 16.45: The sol’y of an ionic cmpd, M2X3 (molar mass=288g) , is 3.6 x 10-17 g/L. What’s the Ksp? • 16.47:What is the pH of a saturated zinc hydroxide sol’n? • 16.48: The pH of a sat’d sol’n of a metal hydroxide, MOH, is 9.68. Calc. the Ksp.

  15. Mix two sol’s together, do you get a ppt (predicting ppt rxns) • Do you get a ppt if mix • 10 mL of 0.0010M AgNO3 and 10 ml of 0.0010M Na2SO4 • 10 mL of 1.0 x 10-6M iron(II) chloride and 20 ml of 3.0 x 10-4M barium hydroxide

  16. 16.50: A volume of 75 mL of 0.060 M NaF is mixed with 25 mL of 0.15 M Sr(NO3)2. Calc the concs in the final soln of NO3-, Na+, Sr2+, and F-. Ksp for SrF2 is 2.0 x 10-10.

  17. 16.8: The common ion effect and solubility • What does Le Chatelier say about the presence of a common ion and solubility • AgI(s)  Ag+(aq) + I-(aq)  add Ag+ from AgNO3 • ___________

  18. Calculate the molar sol’y of SrF2 (Ksp = 2.0 x 10-10) in • water • in 0.010 M Sr(NO3)2 • in 0.010 M NaF • _________ • 16.56 similar

  19. 16.55: How many grams of CaCO3 will dissolve in 300 mL of 0.050 M Ca(NO3)2?

  20. What’s the solubility of Fe(OH)3 in HOH? Ksp for Fe(OH)3 =1.1 x 10-36. • So does changing pH affect solubility of insoluble hydroxides? • 16.62: Calc the pH of Fe(OH)2 in water and at a pH of 7.00, at a pH of 8.00 and at a pH of 10.00. • 16.61: Compare the molar soly of Mg(OH)2 in water and in a soln buffered at a pH of 9.00 .

  21. Factors that affect solubility • 1. _______ • 2. common ion ____________ • 3. pH: salt contains anion (conj base of WA): ____________ • CaF2(s)  Ca2+(aq) + 2F-(aq)  H+

  22. 4. hydroxides--pH: ___ • Except for amphoteric hydroxides as Al(OH)3, Pb(OH)2, Cr(OH)3, Zn(OH)2, Cd(OH)2 • Al(OH)3 + OH-  Al(OH)4-(aq) • As pH increases (add more OH-), tie up the hydroxide salt as a soluble complex,

  23. 5.Complex ion formation • Cu2+(aq) +2OH- Cu(OH)2(s) • Cu(OH)2(s) + 4NH3(aq)  Cu(NH3)42+(aq) complex ion • Cu2+(aq) + 4NH3(aq)Cu(NH3)42+(aq) • Kf = [Cu(NH3)42+] = 5.0 x 1013 [Cu][NH3]4 • Table of formation constants Kf, p 685, table 16.4

  24. 16.67: If 2.50 g of CuSO4 are dissolved in 900 mL of 0.30 M NH3, what sre the concs of Cu2+, Cu(NH3)42+ and NH3 at equilibrium? • 16.70: Calc the molar soly of AgI in a 1.0 M NH3 soln.

  25. Which of the following will be more soluble in acid solution than in water? • BaSO4 • PbCl2 • Fe(OH)3 • CaCO3 • Ca3(PO4)2 • AgBr

  26. 16.54: The molar soly of AgCl in 6.5x10-3M AgNO3 is 2.5 x 10-8 M. In deriving Ksp from these data which of the following assumptions are reasonable? • Ksp is the same as soly. • Ksp of AgCl is the same in 6.5x10-3M AgNO3 as in pure water. • Soly of AgCl is independent of the conc of AgNO3.

  27. [Ag+] in soln does not change significantly upon the addition of AgCl to 6.5x10-3M AgNO3. • [Ag+] in soln after the addition of AgCl to 6.5x10-3M AgNO3 is the same as it would be in pure water.

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