16.6 Solubility Equilibria

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16.6 Solubility Equilibria
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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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• Lets 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.
  _______________

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

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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

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Relationship btn molar soly (s) and Ksp

• Define molar solubility, s ,as the ________
• Let us examine the stoichiometrically different
  salts and their relationship to molar solubility.

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• 11 salt as AgCl, CaCO3
• AgCl(s) ? Ag(aq) Cl-(aq)
• Ksp ____________
• Ag Cl- ____

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• 21 or 12 salt as CaF2 or Ag2SO4
• CaF2(s) ?
• Ksp ________
• F- __ Ca2 __

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• 13 or 31 salt as Fe(OH)3 or Ag3PO4
• Ag3PO4(s) ??
• Ksp
• Ag ___ PO43- ___

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• 23 or 32 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 )

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Ksp and Q (ion-product)

• Remember Ksp refers to a saturated sold, Q
  refers to any soln, not just an equilibrium
  system.
• Ag3PO4(s) ??3Ag(aq) PO43-(aq)
• Ksp Ag3PO43-
• Q Ag3PO43- these need not be equil
  concs

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• If
• Q lt Ksp ______
• Q Ksp ______
• Q gt Ksp _______

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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 soly of Ag3PO4 is
  6.7 x 10-3 g/L

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• 16.45 The soly of an ionic cmpd, M2X3 (molar
  mass288g) , is 3.6 x 10-17 g/L. Whats the Ksp?
• 16.47What is the pH of a saturated zinc
  hydroxide soln?
• 16.48 The pH of a satd soln of a metal
  hydroxide, MOH, is 9.68. Calc. the Ksp.

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Mix two sols 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

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• 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.

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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
• ___________

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• Calculate the molar soly 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

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

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• Whats 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 .

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Factors that affect solubility

• 1. _______
• 2. common ion ____________
• 3. pH salt contains anion (conj base of WA)
  ____________
• CaF2(s) ? Ca2(aq) 2F-(aq) ?
  H

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• 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,

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• 5.Complex ion formation
• Cu2(aq) 2OH- ??Cu(OH)2(s)
• Cu(OH)2(s) 4NH3(aq) ? Cu(NH3)42(aq) comple
  x ion
• Cu2(aq) 4NH3(aq) ??Cu(NH3)42(aq)
• Kf Cu(NH3)42 5.0 x 1013 CuNH34
• Table of formation constants Kf, p 685, table 16.4

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• 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.

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

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• 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.

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• 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.