Saturated Solutions

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Saturated Solutions

• 1. Cannot dissolve any more solute
• 2. Contain undissolved solid
• 3. Ex BaSO4
• BaSO4(s) ? Ba2(aq) SO42-(aq)
• Ksp Ba2SO42-/BaSO4
• Ksp Ba2SO42-

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Writing Ksp

• Examples
• Ca3(PO4)2
• Calcium Carbonate
• Chromium (III)Hydroxide
• Discuss Magnitude of Ksp

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Ksp and Solubility

• 1. NaCl has a solubility of 35.7 g/100 mL. What
  is the molar solubility and Ksp? (Ans 6.10 M,
  37.2)
• 2. CaCl2 has a solubility of 74.5 g/100 mL. What
  is the molar solubility and Ksp? (Ans 6.71 M,
  1.21 X 103)

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Ksp and Solubility

• 3. BaF2 has a molar solubility of 0.0068 M. How
  many grams will dissolve in 600.0 mL? (Ans 0.72
  grams)
• 4. MgI2 has a molar solubility of 5.32 M. How
  many grams will dissolve in 500.0 mL? (Ans 740.
  grams)

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Calculating Ksp

• 1. A saturated soln of AgCl is found to have an
  eq. concentration of Ag 1.35 X 10-5 M.
  Calculate Ksp. (Ans 1.82 X 10-10.)
• 2. A saturated soln of MgF2 is prepared. At eq.
  the concentration of Mg2 is measured to be
  0.0012 M. Calculate Ksp. (Ans 6.9 X 10-9)

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Calculating Ksp

• 3. The solubility of CaF2 is 0.00167 g/100mL.
  What is the Ksp? (Ans 3.8 X 10-11)
• 4. The solubility of Fe(OH)3 is 0.0079 g/L. What
  is the Ksp? (Ans 8.1 X 10-16)
• 5. The solubility of Al2(SO4)3 is 31.3 g/L. What
  is the Ksp? (Ans 6.9 X 10-4)

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Calculating Solubility

• 1. What is the solubility in g/100 mL of CaSO4 if
  the Ksp is 2.4 X 10-5? (Ans 0.067 g/100 mL)
• 2. What is the solubility of CaF2 in g/100 mL if
  the Ksp is 3.9 X 10-11? (Ans 0.0016 g/100mL)

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Calculating Solubility

• The Ksp of Cu(N3)2 is 6.3 X 10-10. How many
  grams of Cu(N3)2 will dissolve in 500 mL? (Ans
  0.0399 grams)
• Cu(N3)2 (s) ?Cu2(aq) 2N3-(aq)

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Common Ion Effect and Solubility

• Common Ions decrease solubility
• CaF2(s) ? Ca2(aq) 2F-(aq)
• a) Add Ca2 (shifts to reactants)
• b) Add F- (shifts to reactants)
• Real world water samples are usually not pure

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Common Ion Effect and Solubility

• Hard Water Contains high concentration of Ca2
  and Mg2.
• a) Comes from minerals
• b) CaCO3 buildup
• CaCO3(s) ? Ca2(aq) CO32-(aq)
• c) Does not lather well

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Common Ion Effect and Solubility
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Common Ion Effect and Solubility

• Soft Water Contains high concs. Of SO42- and
  SO32- .
• a) Lathers too well

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Common Ion Effect and Solubility

• 1. Calculate the molar solubility of CaF2 in a
  solution that is 0.010 M Ca(NO3)2. (Ans 3.1 X
  10-5 M.)
• 2. Calculate the molar solubility of CaF2 in a
  solution that is 0.010 M NaF. (Ans 3.9 X 10-7
  M.)

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Common Ion Effect and Solubility

• 3. What is the molar solubility of Mn(OH)2 in
  0.020 M NaOH? (Ans 4.0 X 10-10)

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Common Ion Effect and Solubility

• Applications
• U(OH)3
• CaCO3 buildup
• FePO4 and water (can get PO4 from soda)

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pH and Solubility

• A. Hydroxides Mg(OH)2 Milk of Magnesia
• Mg(OH)2(s) ? Mg2(aq) 2OH-(aq)
• a) Basic solns LeChatelier (less soluble)
• b) Acidic solns More soluble
• (H OH- ? H2O)

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pH and Solubility

• B. Carbonates More soluble in acidic solns.
• CaCO3(s) 2HCl(aq) ? H2O(l) CO2(g)
  CaCl2(aq)

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pH and Solubility

• 1. What is the molar solubility of Ce(OH)3
  (Ksp1.5 X 10-20) in a soln of pH 7.0? (Ans
  4.9 X 10-6 M)
• 2. What is the molar solubility of Ce(OH)3
  (Ksp1.5 X 10-20) in a soln of pH 13.0? (Ans
  1.5 X 10-17 M)

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pH and Solubility

• 3. What is the molar solubility of Sn(OH)2 in a
  soln of pH 9.2? The Ksp of Sn(OH)2 is 1.41 x
  10-28. (Ans 5.6 X 10-19 M)

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Will a ppt form?

• 1. Q Reaction Quotient (calculate from Initial
  concentrations)
• Q lt Ksp Shifts to prod (no ppt)
• Q Ksp Eq. (ppt)
• Q gt Ksp Shifts to reac.(ppt)
• 2. Our Question Is Q gt Ksp?

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Will a ppt form?

• Will a ppt form if a solution is made such that
  Ca2 0.0104 M and SO42-0.0082 M? (Ans Q
  8.5 X 10-5, ppt forms)

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Will a ppt form?

• 2. Will a ppt form when 100.0 mL of 0.0080 M
  Pb(NO3)2 is added to 400.0 mL of 0.0050 M Na2SO4?
  (Ans Q 6.4 X 10-6 so PbSO4 ppts.)

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Will a ppt form?

• 3. Will a ppt form when 50.0 mL of 0.020 M NaF is
  added to 10.0 mL of 0.010 M Ca(NO3)2? (Ans Q
  4.6 X 10-7 so CaF2 ppts.)

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Will a ppt form?

• Will a ppt. Form at pH 8 for a solution of
  0.0040 M Mg(NO3)2?
• 5. At what pH will a ppt form from a solution of
  0.001 M Ni(NO3)2?

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Selective Precipitation

• You can separate ions based on different
  solubilities
• Can be used to remove harmful ions from water.

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Selective Precipitation

• 1. A soln contains 0.01 M Ag and 0.020 M Pb2
  ions. If NaCl is slowly added to the soln. which
  ion will ppt first? (Ans AgCl will ppt first,
  Cl- 1.8 X 10-8 M)

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Selective Precipitation

• 2. A soln contains 0.050 M Mg2 and 0.020 M Cu2
  ions. If KOH is slowly added to the soln. which
  ion will ppt first? (Ans Cu(OH)2 will ppt
  first, OH- 1.5 X 10-9 M)

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• a) Solubility is how many grams/100 mL dissolve,
  Ksp is an equilibrium constant.
• b). Ksp Mn2CO32-
• Ksp Hg2OH-2
• Ksp Cu23PO43-2