Solubility
Solubility
Saturated Solutions
1. Cannot dissolve any more solute
2. Contain undissolved solid
3. Ex: BaSO4
BaSO4(s)  Ba2+(aq) + SO42-(aq)
Ksp = [Ba2+][SO42-]/[BaSO4]
Ksp = [Ba2+][SO42-]
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Solubility
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Solubility
Writing Ksp
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)
Examples:
Ca3(PO4)2
Calcium Carbonate
Chromium (III)Hydroxide
Discuss Magnitude of Ksp
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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4
Solubility
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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Solubility
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)
6. The solubility of Fe(OH)3 is 0.0079 g/L.
a. Calculate the molar solubility (7.4 X 10-5 M)
b. Calculate Ksp? (Ans: 8.1 X 10-16)
c. Calculate how many grams will dissolve
in 250 mL (0.0020 g)
d. Explain whether you would you expect
the freezing point of the solution to be
higher, lower, or just about that of water.
e. List the proper name of the compound.
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7. The solubility of Al2(SO4)3 is 31.3
g/L. What is the Ksp? (Ans: 6.9 X
Calculating Solubility
10-4)
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Solubility
Calculating Solubility
10. 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)
8. 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)
Cu(N3)2 (s)  Cu2+(aq) + 2N3-(aq)
9. 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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Solubility
Solubility
Common Ion Effect and Solubility
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
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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Solubility
Solubility
Common Ion Effect and Solubility
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Common Ion Effect and Solubility
Soft Water
a) Few minerals
b) Often lathers too well
c) Mg2+ and Ca2+ replaced by Na+
Sulfur Water
Contains high concs. Of SO42- and SO32(turn to H2S)
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Solubility
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.)
What is the molar solubility of Mn(OH)2 in
0.020 M NaOH? (Ans: 4.0 X 10-10)
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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Solubility
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Solubility
Common Ion Effect and Solubility
pH and Solubility
A. Hydroxides – Mg(OH)2 Milk of
Magnesia
Applications
1. U(OH)3
2. CaCO3 buildup
3. FePO4 and water (can get PO4 from soda)
Mg(OH)2(s)  Mg2+(aq) + 2OH-(aq)
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a) Basic solns – LeChatelier (less
soluble)
b) Acidic solns – More soluble
(H+ + OH-  H2O)
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Solubility
Solubility
pH and Solubility
B. Carbonates – More soluble in acidic solns.
CaCO3(s) + 2HCl(aq)  H2O(l) + CO2(g) +CaCl2(aq)
pH and Solubility
1. What is the molar solubility of
Ce(OH)3 (Ksp=1.5 X 10-20) in a soln
of pH 9.0? (Ans: 1.5 X 10-5 M)
2. What is the molar solubility of
Ce(OH)3 (Ksp=1.5 X 10-20) in a soln
of pH 13.0? (Ans: 1.5 X 10-17 M)
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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)
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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Solubility
Will a ppt form?
1. Q = Reaction Quotient (calculate from
Initial concentrations)
Q < Ksp Shifts to prod (no ppt)
Q = Ksp Eq. (ppt)
Q > Ksp Shifts to reac.(ppt)
2. Our Question: Is Q > Ksp?
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Solubility
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Solubility
Will a ppt form?
Will a ppt form?
1. 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)
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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Solubility
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.)
4. Will a ppt. Form at pH = 8 for a
solution of 0.0040 M Mg(NO3)2?
5. At what pH will it form? (9.8)
6. At what pH will a ppt form from
a solution of 0.001 M Ni(NO3)2?
(ANS: 7.89)
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Solubility
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Solubility
Selective Precipitation
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)
1. You can separate ions based on
different solubilities
2. Can be used to remove harmful
ions from water.
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Solubility
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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48.a) Solubility is how many grams/100 mL
dissolve, Ksp is an equilibrium constant.
b). Ksp = [Mn2+][CO32-]
Ksp = [Hg2+][OH-]2
Ksp = [Cu2+]3[PO43-]2
50.a) 4 X 10-6
b) 3.00 X10-8
-5
c) 2.5 X10 g Cu(OH)2
52.6.4 X10-9
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5
Solubility
54.a) 1.82 X10-3 g/L b) 4 X10-11 g/L
c) 1 X10-4 g/L
56. a) 8 X10-4 M
b) 8 X10-8 M
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c) 8 X10 M
64.a) Q = 2 X10-13 ppt
b) Q = 3.3 X10-5 ppt
68. a) 1.1 X10-8 vs. 3.2 X10-5, BaSO4 first
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Three unlabeled bottles are found. They may contain
KNO3, Ca(NO3)2 or Cu(NO3)2. The student labels
them A, B and C. After testing the solutions with
NaOH and Na2SO4, the following results are tabulated.
A
B
C
NaOH
Clear
Cloudy
Clear
Na2SO4
Clear
Clear
Cloudy
i. Identify the contents of each bottle.
ii. At what pH would a ppt form in solution B if we
assume the molarity is about 0.10 M? (4.84)
iii. Write the ionic reaction that occurs between solution
C and Na2SO4.
iv. Calculate the molar solubility of the precipate that
solution C forms with Na2SO4. (4.9 X 10-3)
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