Solubility
• Allows us to flavor foods -- salt & sugar.
• Solubility of tooth enamel in acids.
• Allows use of toxic barium sulfate for
intestinal x-rays.
Solubility Product
• See Table 15.4 on page 759 for
common solubility products.
• Relative solubilities can be predicted by
comparing Ksp values only for salts that
produce the same total number of ions.
•
•
•
•
AgI(s)
Ksp = 1.5 x 10-16
CuI(s)
Ksp = 5.0 x 10-12
CaSO4(s) Ksp= 6.1 x 10-5
CaSO4(s) > CuI(s) > AgI(s)
Solubility Product
•
•
•
•
•
CuS(s)
Ksp = 8.5 x 10-45
Ag2S(s)
Ksp = 1.6 x 10-49
Bi2S3(s)
Ksp= 1.1 x 10-73
Bi2S3(s) > Ag2S(s) > CuS(s)
Why does this order from most to least
soluble appear to be out of order?
Solubility Product
•For solids dissolving to form aqueous
solutions.
•Bi2S3(s)  2Bi3+(aq) + 3S2(aq)
•Ksp = solubility product constant
•and
Ksp = [Bi3+]2[S2]3
Why is Bi2S3(s) not included in the solubilty
product expression?
Solubility Product
•“Solubility” = s = concentration of Bi2S3
that dissolves. The [Bi3+] is 2s and the
[S2] is 3s.
•Note:
Ksp is constant (at a given
temperature)
•
s is variable (especially with a
common
ion present)
Solubility product is an
equilibrium constant and has
Solubility Product Calculations
• Cupric iodate has a measured solubility of
3.3 x 10-3 mol/L. What is its solubility
product?
• Cu(IO3)2(s) <---> Cu2+(aq) + 2 IO3-(aq)
• 3.3 x 10-3 M ---> 3.3 x 10-3 M + 6.6 x 10-3 M
• Ksp = [Cu2+][IO3-]2
• Ksp = [3.3 x 10-3][6.6 x 10-3]2
• Ksp = 1.4 x 10-7
Solubility Product Calculations
• If a 0.010 M solution of sodium iodate is
mixed with a 0.0010 M cupric nitrate, will a
precipitate form?
• 2 NaIO3(aq) + Cu(NO3)2(aq) ---> Cu(IO3)2(s) + 2
NaNO3(aq)
• Cu(IO3)2(s) <---> Cu2+(aq) + 2 IO3-(aq)
• Qsp = [Cu2+][IO3-]2
• Qsp = [1.0 x 10-3][1.0 x 10-2]2
• Qsp = 1.0 x 10-7
Qsp < Ksp  no precipitate
forms.
Solubility Product Calculations
• Cu(IO3)2(s) <---> Cu2+(aq) + 2 IO3-(aq)
• Ksp = [Cu2+][IO3-]2
• If solid cupric iodate is dissolved in HOH;
double & square the iodate concentration.
• If mixing two solutions, one containing Cu2+ and
the other IO3-, then use the concentration of
iodate and only square it.
Common Ion Effect
• CaF2(s) <---> Ca2+(aq) + 2F-(aq)
• What will be the effect on this
equilibrium if solid sodium fluoride is
added? Explain.
• Equilibrium will shift to the left, due to Le
Chatelier’s Principle. Solubility product
must stay constant, so the amount of
Ca2+ & F- must decrease by forming
solid CaF2.
• See Sample Exercise 15.15 on pages
pH & Solubility
• If a solid precipitate has an anion Xthat is an effective base (HX is a weak
acid), then the salt MX will show
increased solubility in an acidic solution.
• Salts containing OH-, S2-, CO32-, C2O42-,
& CrO42- are all soluble in acidic
solution.
• Limestone caves are made up of
insoluble CaCO3, but dissolve in acidic
rain water (H2CO3).
Ion Product, Qsp
• If 750.0 mL of 4.00 x 10-3 M Ce(NO3)3 is
added to 300.0 mL of 2.00 x 10-2 M
KIO3, will Ce(IO3)3 precipitate?
•
•
•
•
•
•
[Ce3+] = (750.0 mL)(4.00 x 10-3 mol/mL)
(750.0 mL + 300.0 mL)
[Ce3+] = 2.86 x 10-3 M
[IO3-] = (300.0 mL)(2.00 x 10-2 mmol/mL)
(750.0 mL + 300.0 mL)
[IO3-] = 5.71 x 10-3 M
Ion Product, Qsp
Continued
• Qsp = [Ce3+]0[IO3-]o3
• Qsp = [2.86 x 10-3][5.72 x 10-3]3
• Qsp = 5.32 x 10-10
• Qsp > Ksp  -10
Ce(IO3)3 will precipitate.
Ksp = 1.9 x 10
Progressive
Precipitation
A Solubility Experience
An experiment to show the effect
of solubility on an equilibrium
system!
Solutions of:
AgNO3
Na2SO4
K2CrO4
(NH4)2S
NaCl
If AgNO3 is mixed with Na2SO4 what ions are most
abundant in the solution?
AgNO3
Na2SO4
K2CrO4
(NH4)2S
NaCl
With what ions is the solution saturated?
2AgNO3(aq) + Molecular
Na2SO4(aq)
 2NaNO3 (aq) +
Equation
Ag2SO4(s)
+
2Ag+(aq) + 2NO3-(aq) +Overall
2Na+(aq) Ionic
+ SO42-Equation
(aq)  2Na (aq) + 2NO3 (aq) + Ag2SO4(s)
+
2AgNet
SO42-(aq)
 Ag2SO4(s)
Equation
(aq) +Ionic
First Precipitation
Silver Sulfate
Precipitate
Ksp = 1.2  10-5
Ag2SO4(s)  2Ag+(aq) + SO42-(aq)
Ksp = [Ag+]2 [SO42-] = 1.2  10-5
Ksp = [2x]2  [x] = 1.2  10-5
Molar Solubility = 1.4  10-2 mol/liter
Silver Sulfate
Precipitate
What ions will be most abundant in the solution
when these are mixed?
Silver
Sulfate
Precipitate
Potassium
Chromate
solution
With what ions will the solution be saturated?
Second Reaction
Silver
Potassium
Sulfate
Chromate
Precipitate solution
Ag2SO4(s) + K2CrO
K2SO4(aq) + Ag2CrO4(s)
Molecular
4(aq) Equation
2Ag2SO4(s) + 2K+Overall
2K+(aq) + SO42-(aq) + Ag2CrO4(s)
Equation
(aq) + CrO4Ionic
(aq) 
2Ag2SO4(s) + Net
CrO4Ionic
Ag2CrO4(s) + SO4 2-(aq)
Equation
(aq) 
Silver
Chromate
precipitate
Ksp = 9.0  10-12
Ag2CrO4(s)  2Ag+(aq) + CrO42-(aq)
Ksp = [Ag+]2 [CrO42-] = 9.0  10-12
Ksp = [2x]2  [x] = 9.0  10-12
Molar Solubility = 1.3  10-4 mol/liter
Silver
Chromate
precipitate
Ksp = 9.0  10-12
What ions will be most abundant in the solution when
NaCl solution is added to Ag2CrO4 precipitate?
With what ions will the solution be saturated?
Third Reaction
Ag2CrO4(s) + 2NaCl
Na2CrO4(aq) + 2AgCl(s)
Molecular
(aq) Equation
+
Ag2CrO4(s) + 2Na
2Na+(aq) + CrO42-(aq) + 2AgCl(s)
Overall
Ionic
Equation
(aq) + 2Cl
(aq) 
Ag2CrO4(s)
+ 2Cl
 2AgCl(s) + CrO4 2Net
Ionic
(aq) Equation
Silver
Chloride
precipitate
Ksp = 9.0  10-12
AgCl(s)  Ag+(aq) + Cl-(aq)
Ksp = [Ag+] [Cl-] = 1.6  10-10
Ksp = [x]  [x] = 1.6  10-10
Molar Solubility = 1.3  10-5 mol/liter
Silver
Chloride
precipitate
Ksp = 1.6  10-10
What ions will be most abundant in the solution when
(NH4)2S solution is added to AgCl precipitate?
With what ions will the solution be saturated?
Fourth Reaction
2AgCl(s) + (NHMolecular
2NH4Cl(aq) + Ag2S(s)
Equation
4)2S(aq) 
+
22AgCl(s) + 2NH
2NH4+ (aq) + 2Cl-(aq) + Ag2S(s)
Overall
Equation
4 (aq) + SIonic
(aq) 
22AgClNet
Ag2S(s) + 2Cl-(aq)
Equation
(s) + SIonic
(aq) 
Silver
Chloride
precipitate
Ksp = 9.0  10-12
Ag2S(s)  2Ag+(aq) + S2-(aq)
Ksp = [Ag+]2 [S2-] = 1.6  10-49
Ksp = [2x]2  [x] = 1.6  10-49
Molar Solubility = 3.4  10-17 mol/liter
Silver
Chloride
precipitate
Ksp = 1.6  10-49
Of the four “insoluble” compounds, which one is the
most insoluble?
Molar Solubility of Ag2SO4 = 1.4  10-2 mol/liter
Molar Solubility of Ag2CrO4 = 1.3  10-4 mol/liter
Molar Solubility of AgCl = 1.3  10-5 mol/liter
Molar Solubility of Ag2S = 3.4  10-17 mol/liter
Of the four “insoluble” compounds, which one is the
least insoluble?
Molar Solubility of Ag2SO4 = 1.4  10-2 mol/liter
Molar Solubility of Ag2CrO4 = 1.3  10-4 mol/liter
Molar Solubility of AgCl = 1.3  10-5 mol/liter
Molar Solubility of Ag2S = 3.4  10-17 mol/liter
Qualitative Analysis
• The separation of ions by selective
precipitation.
• Much descriptive chemistry can be
learned from qualitative analysis.
• Qualitative analysis can be done for
both cations and anions.
Qualitative Analysis
• Group I -- Insoluble chlorides -- Ag+,
Pb2+, & Hg22+
• Group II -- Sulfides insoluble in acid
solution -- Hg2+, Cd2+, Bi3+, Cu2+, & Sn4+
• Group III -- Sulfides insoluble in basic
solution -- Co2+, Zn2+, Mn2+, Ni2+, & Fe3+
• Group IV -- Insoluble carbonates --Ba2+,
Ca2+, & Mg2+
• Group V -- alkali metal and ammonium
ions -- soluble so must be identified by
flame tests, etc.