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Understanding the Solubility of Metal Hydroxides and Carbonates in Aqueous Solutions

This document delves into the solubility equilibria of various metal hydroxides and carbonates in aqueous solutions, showcasing how factors such as pH and the presence of hydroxide ions influence solubility. Through examples like the solubility product constants (Ksp) for Zn(OH)2 and CaCO3, we explore the relationships between concentration and precipitation. Additionally, we examine how lowering pH increases the solubility of Zn(OH)2 and how common ions affect the solubility of salts derived from weak acids.

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Understanding the Solubility of Metal Hydroxides and Carbonates in Aqueous Solutions

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  1. Class average for Exam I 70

  2. Fe3+(aq) + 3 OH-(aq) Fe(OH)3 [Fe3+][OH-]3 = 1.1 x 10-36 [y][3y]3 = 1.1 x 10-36 If there is another source of OH- (NaOH) that provides a higher [OH-] then that is the value of [OH-] to be used.

  3. pH and solubility

  4. CaCO3(s) + H3O+(aq) Ca2+(aq) + HCO3-(aq) + H2O(l)

  5. CaCO3(s) + H3O+(aq) Ca2+(aq) + HCO3-(aq) + H2O(l) Net ionic equation.

  6. CaCO3(s) + H3O+(aq) Ca2+(aq) + HCO3-(aq) + H2O(l) CaCO3 calcium carbonate, present in both limestone and marble.

  7. CaCO3(s) + H3O+(aq) Ca2+(aq) + HCO3-(aq) + H2O(l) CaCO3(s) + H2O(l) Ca2+(aq) + CO32-(aq)

  8. Ksp = [Ca2+][CO32-] CaCO3(s) + H3O+(aq) Ca2+(aq) + HCO3-(aq) + H2O(l) CaCO3(s) + H2O(l) Ca2+(aq) + CO32-(aq) CO32-(aq) + H3O+(aq) H2O(l) + HCO3-(aq)

  9. Ksp = [Ca2+][CO32-] CaCO3(s) + H3O+(aq) Ca2+(aq) + HCO3-(aq) + H2O(l) CaCO3(s) + H2O(l) Ca2+(aq) + CO32-(aq) CO32-(aq) + H3O+(aq) H2O(l) + HCO3-(aq) Any reaction favoring the formation of HCO3- favors the solution of a solid carbonate .

  10. Zn(OH)2(s) Zn2+(aq) + 2 OH-(aq)

  11. Zn(OH)2(s) Zn2+(aq) + 2 OH-(aq) [Zn2+][OH-]2 = Ksp

  12. Zn(OH)2(s) Zn2+(aq) + 2 OH-(aq) [Zn2+][OH-]2 = Ksp = 4.5 x 10-17

  13. Zn(OH)2(s) Zn2+(aq) + 2 OH-(aq) [Zn2+][OH-]2 = Ksp = 4.5 x 10-17 Increase solubility of Zn(OH)2 by lowering pH.

  14. Zn(OH)2(s) Zn2+(aq) + 2 OH-(aq) [Zn2+][OH-]2 = Ksp = 4.5 x 10-17 Increase solubility of Zn(OH)2 by lowering pH. Removal of product, OH-, shifts equilibrium to right.

  15. Zn(OH)2(s) Zn2+(aq) + 2 OH-(aq) [Zn2+][OH-]2 = Ksp = 4.5 x 10-17 [Zn2+] = ? @ pH = 7

  16. Zn(OH)2(s) Zn2+(aq) + 2 OH-(aq) [Zn2+][OH-]2 = Ksp = 4.5 x 10-17 [Zn2+] = ? @ pH = 7 [Zn2+] = y

  17. Zn(OH)2(s) Zn2+(aq) + 2 OH-(aq) [Zn2+][OH-]2 = Ksp = 4.5 x 10-17 [Zn2+] = ? @ pH = 7 [Zn2+] = y (y)(2y)2 = Ksp

  18. Zn(OH)2(s) Zn2+(aq) + 2 OH-(aq) [Zn2+][OH-]2 = Ksp = 4.5 x 10-17 [Zn2+] = ? @ pH = 7 [Zn2+] = y (y)(2y)2 = Ksp = 4y3 = 4.5 x 10-17

  19. Zn(OH)2(s) Zn2+(aq) + 2 OH-(aq) [Zn2+][OH-]2 = Ksp = 4.5 x 10-17 [Zn2+] = ? @ pH = 7 [Zn2+] = y (y)(2y)2 = Ksp = 4y3 = 4.5 x 10-17 [Zn2+] = 2.2 x 10-6 M [OH-] = 4.4 x 10-6 M

  20. Zn(OH)2(s) Zn2+(aq) + 2 OH-(aq) [Zn2+][OH-]2 = Ksp = 4.5 x 10-17 [Zn2+] = ? @ pH = 6 buffered [Zn2+] = y pH = 6, [H3O+] = 10-6 Kw [OH-] = [H3O+]

  21. Zn(OH)2(s) Zn2+(aq) + 2 OH-(aq) [Zn2+][OH-]2 = Ksp = 4.5 x 10-17 [Zn2+] = ? @ pH = 6 buffered [Zn2+] = y pH = 6, [H3O+] = 10-6 Kw 1 x 10-14 = [OH-] = = 10-8 [H3O+] 10-6

  22. Zn(OH)2(s) Zn2+(aq) + 2 OH-(aq) [Zn2+][OH-]2 = Ksp = 4.5 x 10-17 [OH-] = 1 x 10-8 (y)(1 x 10-8)2 = 4.5 x 10-17

  23. Zn(OH)2(s) Zn2+(aq) + 2 OH-(aq) [Zn2+][OH-]2 = Ksp = 4.5 x 10-17 [OH-] = 1 x 10-8 (y)(1 x 10-8)2 = 4.5 x 10-17 4.5 x 10-17 y = 1 x 10-16

  24. Zn(OH)2(s) Zn2+(aq) + 2 OH-(aq) [Zn2+][OH-]2 = Ksp = 4.5 x 10-17 [OH-] = 1 x 10-8 (y)(1 x 10-8)2 = 4.5 x 10-17 4.5 x 10-17 y = = 4.5 x 10-1 1 x 10-16

  25. Zn(OH)2(s) Zn2+(aq) + 2 OH-(aq) [Zn2+][OH-]2 = Ksp = 4.5 x 10-17 [OH-] = 1 x 10-8 (y)(1 x 10-8)2 = 4.5 x 10-17 4.5 x 10-17 y = = 4.5 x 10-1 1 x 10-16 [Zn2+] = 0.45 M

  26. Zn(OH)2(s) Zn2+(aq) + 2 OH-(aq) [Zn2+][OH-]2 = Ksp = 4.5 x 10-17 pH = 7 [Zn2+] = 0.0000022 M [Zn2+] = 0.45 M pH = 6

  27. Zn(OH)2(s) Zn2+(aq) + 2 OH-(aq) [Zn2+][OH-]2 = Ksp = 4.5 x 10-17 pH = 7 [Zn2+] = 0.0000022 M [OH-] = 2[Zn2+] [Zn2+] = 0.45 M pH = 6

  28. Zn(OH)2(s) Zn2+(aq) + 2 OH-(aq) [Zn2+][OH-]2 = Ksp = 4.5 x 10-17 pH = 7 [Zn2+] = 0.0000022 M [OH-] = 2[Zn2+] = 4.4 x 10-6 M [Zn2+] = 0.45 M pH = 6

  29. Zn(OH)2(s) Zn2+(aq) + 2 OH-(aq) [Zn2+][OH-]2 = Ksp = 4.5 x 10-17 pH = 8.6 [Zn2+] = 0.0000022 M [OH-] = 2[Zn2+] = 4.4 x 10-6 M [Zn2+] = 0.45 M pH = 6

  30. Solubility of salts of weak acids

  31. Solubility of salts of weak acids HA(aq) + H2O(l) H3O+(aq) + A-(aq)

  32. Solubility of salts of weak acids HA(aq) + H2O(l) H3O+(aq) + A-(aq) Reduce pH, increase [H3O+]

  33. Solubility of salts of weak acids HA(aq) + H2O(l) H3O+(aq) + A-(aq) Reduce pH, increase [H3O+] Increase [H3O+] : equilibrium

  34. Solubility of salts of weak acids HA(aq) + H2O(l) H3O+(aq) + A-(aq) NaA(s) Na+(aq) + A-(aq) conjugate base

  35. Solubility of salts of weak acids HA(aq) + H2O(l) H3O+(aq) + A-(aq) NaA(s) Na+(aq) + A-(aq) A-(aq) + H3O+(aq) HA(aq) + H2O(l)

  36. Solubility of salts of weak acids HA(aq) + H2O(l) H3O+(aq) + A-(aq) NaA(s) Na+(aq) + A-(aq) A-(aq) + H3O+(aq) HA(aq) + H2O(l) Reduce pH, increase [H3O+]

  37. Solubility of salts of weak acids HA(aq) + H2O(l) H3O+(aq) + A-(aq) NaA(s) Na+(aq) + A-(aq) A-(aq) + H3O+(aq) HA(aq) + H2O(l) Reduce pH, increase [H3O+], reduce [A-]

  38. Solubility of salts of weak acids HA(aq) + H2O(l) H3O+(aq) + A-(aq) NaA(s) Na+(aq) + A-(aq) A-(aq) + H3O+(aq) HA(aq) + H2O(l) Reduce pH, increase [H3O+], reduce [A-], increase [Na+]

  39. Using common ions to separate mixtures of ions.

  40. Using common ions to separate mixtures of ions. Separating ions which share a group is difficult - they have very similar chemistries.

  41. Using common ions to separate mixtures of ions. I II VII Na+ Ca2+ Cl- K+ Ba2+ I-

  42. M1X M1+ + X- M2X M2+ + X-

  43. M1X M1+ + X- M2X M2+ + X- If the solution is not saturated for either M1X or M2X, there will be no solid present.

  44. M1X M1+ + X- M2X M2+ + X- As [X-] is increased, at some point precipitation will occur.

  45. M1X M1+ + X- M2X M2+ + X- If Ksp for M1X and Ksp for M2X differ by a large enough amount, one will precipitate and the other will remain in solution.

  46. CaF2(s) Ca2+(aq) + 2 F-(aq) BaF2(s) Ba2+(aq) + 2 F-(aq)

  47. CaF2(s) Ca2+(aq) + 2 F-(aq) BaF2(s) Ba2+(aq) + 2 F-(aq) CaF2Ksp = 3.9 x 10-11 BaF2Ksp = 1.7 x 10-6

  48. CaF2(s) Ca2+(aq) + 2 F-(aq) BaF2(s) Ba2+(aq) + 2 F-(aq) CaF2Ksp = 3.9 x 10-11 BaF2Ksp = 1.7 x 10-6 Q < Ksp no precipitate

  49. CaF2(s) Ca2+(aq) + 2 F-(aq) BaF2(s) Ba2+(aq) + 2 F-(aq) CaF2Ksp = 3.9 x 10-11 BaF2Ksp = 1.7 x 10-6 Q = [Ba2+][F-]2 < 1.7 x 10-6

  50. CaF2(s) Ca2+(aq) + 2 F-(aq) BaF2(s) Ba2+(aq) + 2 F-(aq) CaF2Ksp = 3.9 x 10-11 BaF2Ksp = 1.7 x 10-6 Q = [Ba2+][F-]2 < 1.7 x 10-6 Q < Ksp no precipitate

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