solubility allows us to flavor foods -- salt & sugar. solubility of tooth enamel in acids....

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 only one value for a given solid at a given temperature. Solubility is an equilibrium position.

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 764-765.

pH & Solubility• If a solid precipitate has an anion X-

that 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-, C2O4

2-, & CrO4

2- 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 Ce(IO3)3 will precipitate.Ksp = 1.9 x 10 -10

Progressive PrecipitationA Solubility Experience

An experiment to show the effect of solubility on an equilibrium

system!

Solutions of:

AgNO3

Na2SO4

K2CrO4

NaCl

(NH4)2S

If AgNO3 is mixed with Na2SO4 what ions are most abundant in the solution?

AgNO3

Na2SO4

K2CrO4

NaCl

(NH4)2S

With what ions is the solution saturated?

2AgNO3(aq) + Na2SO4(aq) 2NaNO3 (aq) + Ag2SO4(s)

Ksp = 1.2 10-5

Silver Sulfate

Precipitate

2Ag+(aq)

+ 2NO3-(aq) + 2Na+

(aq) + SO42-

(aq) 2Na+(aq) + 2NO3

- (aq) + Ag2SO4(s)

2Ag+(aq)

+ SO42-

(aq) Ag2SO4(s)

First Precipitation

Molecular Equation

Overall Ionic Equation

Net Ionic Equation

Silver Sulfate

Precipitate

Ag2SO4(s) 2Ag+(aq)

+ SO42-

(aq)

Ksp = [Ag+]2 [SO42-] = 1.2

10-5Ksp = [2x]2 [x] = 1.2 10-5

Molar Solubility = 1.4 10-2 mol/liter

Silver Sulfate Precipitate

Potassium Chromate solution

What ions will be most abundant in the solution when these are mixed?

With what ions will the solution be saturated?

Silver Sulfate Precipitate

Second Reaction

Potassium Chromate solution

Ag2SO4(s) + K2CrO4(aq) K2SO4(aq) + Ag2CrO4(s)

Ksp = 9.0 10-12

Ag2SO4(s) + 2K+(aq) + CrO4

2-(aq) 2K+

(aq) + SO42-

(aq) + Ag2CrO4(s)

Ag2SO4(s) + CrO4

2-(aq) Ag2CrO4(s) + SO4

2-(aq)

Molecular Equation


Net Ionic Equation

Silver Chromate precipitate

Ksp = 9.0 10-12

Silver Chromate precipitate

Ag2CrO4(s) 2Ag+(aq)

+ CrO42-

(aq)

Ksp = [Ag+]2 [CrO42-] = 9.0 10-

12Ksp = [2x]2 [x] = 9.0 10-12


What ions will be most abundant in the solution when NaCl solution is added to Ag2CrO4

precipitate?


Third Reaction

Ag2CrO4(s) + 2NaCl(aq) Na2CrO4(aq) + 2AgCl(s)

Ksp = 9.0 10-12

Ag2CrO4(s) + 2Na+(aq) + 2Cl-(aq) 2Na+

(aq) + CrO42-

(aq) + 2AgCl(s)

Ag2CrO4(s) + 2Cl-(aq) 2AgCl(s) + CrO4

2-

Molecular Equation


Net Ionic Equation

Silver Chloride precipitate

Ksp = 1.6 10-10


AgCl(s) Ag+(aq)

+ Cl-(aq)

Ksp = [Ag+] [Cl-] = 1.6 10-10

Ksp = [x] [x] = 1.6 10-10


What ions will be most abundant in the solution when (NH4)2S solution is added to AgCl precipitate?


Fourth Reaction

2AgCl(s) + (NH4)2S(aq) 2NH4Cl(aq) + Ag2S(s)

Ksp = 9.0 10-12

2AgCl(s) + 2NH4+ (aq) + S2-

(aq) 2NH4+

(aq) + 2Cl-(aq) + Ag2S(s)

2AgCl(s) + S2-

(aq) Ag2S(s) + 2Cl-(aq)

Molecular Equation


Net Ionic Equation


Ksp = 1.6 10-49


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

Of the four “insoluble” compounds, which one is the most insoluble?

Molar Solubility of Ag2S = 3.4 10-17 mol/liter

Molar Solubility of AgCl = 1.3 10-5 mol/liter

Molar Solubility of Ag2CrO4 = 1.3 10-4 mol/liter

Molar Solubility of Ag2SO4 = 1.4 10-2 mol/liter


Of the four “insoluble” compounds, which one is the least insoluble?


Molar Solubility of AgCl = 1.3 10-5 mol/liter

Molar Solubility of Ag2CrO4 = 1.3 10-4 mol/liter

Molar Solubility of Ag2SO4 = 1.4 10-2 mol/literMolar Solubility of Ag2SO4 = 1.4 10-2 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.

solubility allows us to flavor foods -- salt & sugar. solubility of tooth enamel in acids....

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