please pick up solubility products constants data sheet heterogeneous equilibria problem set
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Heterogeneous Equilibria
Edward A. Mottel
Department of Chemistry
Rose-Hulman Institute of Technology
04/18/23
Heterogeneous Equilibria
• Reading assignment: Fine, Beall & Stuehr, Chapter 10.5
• Sparingly soluble salts• Solubility product• Common ion effect• Molar solubility• Applications
04/18/23
Some Salts are Soluble
• Soluble salts
• Group IA, NH4+, NO3
–, ClO3–, ClO4
–
• Most halides (Cl–, Br–, I–)
• except Ag+, Cu+, Hg22+, Pb2+
• Most sulfates
• except CaSO4, BaSO4, Ag2SO4, HgSO4, PbSO4
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Some Salts are Not Very Soluble
• Sparingly soluble salts• Most hydroxides
• except Group IA, Ba(OH)2
• Carbonates, phosphates, sulfides• except Group IA, NH4
+
• Solubility depends on• Temperature and solvent
• Strong electrolyte
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Sparingly Soluble Salts
AgCl (s) Ag+(aq) + Cl–(aq)
The solubility product of silver chloride is 1.8 x 10-10, how can it be a strong electrolyte?
AgCl (s) AgCl (aq)
This indicates that AgClisn’t very soluble.(sparingly soluble)
Ag+(aq) + Cl–(aq)
This indicates that theamount of AgCl which dissolves
ionizes extensively.(strong electrolyte)
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Solubility Product, Ksp
• Products over reactants with simplifications
[Ag+] [Cl–]
[AgCl(s)]Kc
[Ag+] [Cl–] = Kc · [AgCl(s)]
[Ag+] [Cl–] = Ksp
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For Each of the Following Determine the Solubility Product Expression
• lead(II) carbonate• calcium fluoride• iron(III) hydroxide
• iron(II) sulfide• lead(II) iodide• silver sulfate
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For Each of the Following Determine the Solubility Product Expression
• [Pb2+] [CO32–]
• [Ca2+] [F–]2 • [Fe3+] [OH–]3
• [Fe2+] [S2–]• [Pb2+] [I–]2 • [Ag+]2 [SO4
2–]
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How to Determine If a Compound is Soluble or Not?
• Solubility Rules• Table of Solubility Product Constants• Handbook of Chemistry and Physics
• Physical Constants of Inorganic Compounds
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Physical Constants of Inorganic Compounds
• Name• Formula• Molecular Weight• Crystalline Form
• Color• Density
• Melting Point• Boiling Point• Solubility
• Cold Water• Hot Water• Other Solvents
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Copper(II) Formate
• Formula and Molecular Weight
• Cu(HCOO)2, 153.55 amu
• Color• blue, monoclinic crystals
• Is copper(II) formate soluble in water?• yes, 12.5 grams per 100 mL of water• greater than 1 gram per 100 mL water
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Group Activity
• An aqueous solution of copper(II) nitrate is mixed with aqueous sodium iodate.• Write an equation for this process and use
appropriate tables to determine if a reaction occurs.
• What observations are expected to be made?
• Is Cu(NO3)2 soluble?• Is NaIO3 soluble?
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Copper(II) Iodate
Cu2+(aq) + 2 NO3–(aq) + 2 Na+(aq) + 2 IO3
–(aq)
Cu(IO3)2(s) + 2 NO3–(aq) + 2 Na+(aq)
Ionic Equation:
Cu2+(aq) + 2 IO3–(aq) Cu(IO3)2(s)
Net Ionic Equation:
04/18/23
Copper(II) Iodate
• Sparingly soluble• less than 1 gram per 100 mL of water• 0.136 grams per 100 mL of water at 15 °C
Cu2+(aq) + 2 IO3–(aq) Cu(IO3)2(s)
• Green, monoclinic crystals
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Pre-laboratory Assignment
• Experiment Q: Qualitative Analysis• Complete the Predicted Reactions grid on
page Q-3 in laboratory manual • Predict double displacement reactions, use
• Solubility Rules• Table of Solubility Product Constants• Handbook of Chemistry and Physics
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Al2(SO4)3
ZnCl2
Al2(SO4)3 + ZnCl2 AlCl3 + ZnSO4
predicted to be solublepredicted to be soluble
NR
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Al2(SO4)3
ZnCl2 NR
BaCl2
Al2(SO4)3 + BaCl2 AlCl3 + BaSO4
predicted to be solublepredicted to be an insoluble, white ppt
BaSO4
white ppt
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Two Beakers Each Contain500 mL of Water
50 grams of PbF2 is added to Beaker 1
400 grams of PbF2 is added to Beaker 2
Some of the solid dissolves.
In which beaker will morelead(II) fluoride dissolve?
04/18/23
Solubility Product
• What is the solubility of lead(II) fluoride in pure water?• Write the chemical equation for the
dissolution process.• Let +x be the moles per liter of lead(II) ion
that is produced.• Write the mass-action expression.• Substitute variables and solve the solubility
product mass-action expression.
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Lead(II) Fluoride
-x +x +2x
x = 2.1 x 10–3 M
• What does 2.1 x 10–3 M represent?
PbF2(s) Pb2+(aq) + 2 F–(aq)
• Molar solubility of PbF2 in pure water
• Molarity of lead(II) ion in solution• What is the molarity of the fluoride ion?
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How many grams of lead(II) fluoride will dissolve in 500 mL of
water?
• Molar solubility of PbF2 (FW 245.2 amu) in pure water is 2.1 x 10–3 M
2.1 10–3moles PbF2
liter
0.500 liter
245.2 grams PbF2
moles PbF2
0.26 g PbF2
04/18/23
Each beaker contains 500 mL of water.
50 grams of PbF2 is added to Beaker 1
400 grams of PbF2 is added to Beaker 2
If there is excess solid at equilibrium,the same amount dissolves!
In which beaker will more lead(II) fluoride dissolve?
04/18/23
Two beakers each contain500 mL of solution
• 50 grams of PbF2 is added to pure water
• 50 grams of PbF2 is added to 0.0200 M sodium fluoride
Into which solution will morelead(II) fluoride dissolve?
H2OH2O
Na+F-
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Common Ion Effect
• Equilibrium concentrations of each ion depend on the number of those ions in solution, regardless of the source.
What is the molar solubility of lead(II) fluoridein a solution containing 0.0200 M sodium fluoride?
Assume one liter of solution
04/18/23
The Molar Solubility of Lead(II) Fluoridein 0.0200 M Sodium Fluoride
PbF2(s) Pb2+(aq) + 2 F–(aq)
0.0200
-x +x +2x
Ksp = [Pb2+] [F–]2 = 3.7 x 10–8 M3
Ksp = (x) (0.0200 + 2x)2 = 3.7 x 10–8 M3
x = 9.2 x 10–5 Mx = 0.023 g in one liter
04/18/23
Group Activity
Why is the molar solubility oflead(II) fluoride different in a solution
containing sodium fluoride?
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Group Activity
PbF2(s) Pb2+(aq) + 2 F–(aq)
Why is the molar solubility of lead(II) fluoridedifferent in a solution containing sodium fluoride?
Explain in terms of Le Châtelier’s Principle
04/18/23
Selective Precipitation
A solution contains0.100 M cadmium ion
0.050 M iron(III) ion
0.200 M nickel(II) ion
If sodium hydroxide is slowly added to
the solution
What precipitates will form?In what order will the precipitates form?
04/18/23
Selective Precipitation Strategy
Determine the hydroxide ion concentrationneeded to precipitate each metal.
Determine the order in which thosehydroxide ion concentrations will be reached.
0.100 M cadmium ion
0.050 M iron(III) ion
0.200 M nickel(II) ion
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Hydroxide Ion Concentration Neededto Precipitate 0.100 M Cd2+
Cd(OH)2(s) Cd2+(aq) + 2 OH–(aq)
[Cd2+] [OH–]2 = Ksp
[0.100] [OH–]2 = 2.0 x 10–14 M3
[OH–] =2.0 x 10–14 M3
[0.100]
1/2
[OH–] = 4.5 x 10–7 M
04/18/23
Hydroxide Ion Concentration Neededto Precipitate
• 0.100 M Cd2+
• [OH–] = 4.5 x 10–7 M• 0.050 M Fe3+
• [OH–] = 1.1 x 10–12 M• 0.200 M Ni2+
• [OH–] = 2.8 x 10–8 M
As the solution is slowly made basic,which precipitates first?
10–5
10–6
10–7
10–8
10–9
10–10
10–11
10–12
10–13
10–14
[OH–]
Cd(OH)2
Fe(OH)3
Ni(OH)2Bas
ic
04/18/23
Selective Precipitation
At what pH will the last metal ion
begin to precipitate?
9876543210
pH
7.65
When the cadmium ion begins to
precipitate how much of the iron(III)
ion is still in solution?
10–5
10–6
10–7
10–8
10–9
10–10
10–11
10–12
10–13
10–14
[OH–]
Cd(OH)2
Ni(OH)2
Fe(OH)3
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Selective Precipitation
• 0.100 M cadmium ion begins to precipitate when the hydroxide ion concentration is 4.5 x 10–7 M.
• What is the maximum iron(III) ion concentration under these conditions?
04/18/23
Selective Precipitation
Fe(OH)3(s) Fe3+(aq) + 3 OH–(aq)
[Fe3+] [OH–]3 = Ksp
[Fe3+] (4.5 x 10–7 M)3 = 6.0 x 10–38 M4
[Fe3+] =6.0 x 10–38 M4
(4.5 x 10–7 M )3
[Fe3+] = 6.6 x 10–19 M
04/18/23
Determination ofMolar Solubility and Ksp
• The Handbook of Chemistry and Physics indicates that the solubility of zinc fluoride (FW 103.37) is 1.62 grams per 100 mL of water.• What is the molar solubility of zinc
fluoride?• What is the solubility product of zinc
fluoride?
04/18/23
Zinc FluorideMolar Solubility
1.62 g /100 mL water
16.2 g /1000 mL water
16.2 g /1000 mL solution
16.2 g /103.37 g·mol–1 = 0.157 mol ZnF2
The molar solubility of zinc fluoride is 0.157 M.
04/18/23
Zinc FluorideSolubility Product
ZnF2(s) Zn2+(aq) + 2 F–(aq)
Ksp = [Zn2+] [F–]2
Ksp = (0.157 M) (2 x 0.157 M)2
Two moles of fluoride ionform for every zinc ion.
Ksp = (0.157 M) (0.314 M)2
Ksp = 1.54 x 10–2 M3