CH186
Solubility Equilibrium Exam Questions
From Spring 2001 Semester
1)For each of the following, carry out the indicated calculations.
a.Calculate the molar solubility of zinc oxalate, ZnC2O4 (Ksp = 2.7 x 10-8).
b.Calculate the molar solubility of silver carbonate, Ag2CO3
(Ksp = 8.1 x 10-12). (CO32- = carbonate ion)
c.Calculate the approximate Ksp value for lanthanum iodate, La(IO3)3 (FW = 664 g/mol), if a 2.0 L solution saturated at 25C with La(IO3)3 yielded 0.916 g of La(IO3)3 upon evaporation. (IO3- = iodate ion)
2)A 3.0 L sample of industrial wastewater solution is known to contain 0.085 M Cd2+(aq). Because Cd2+ is toxic, it is desirable to remove this ion before disposal. If the pH of this solution is adjusted to 8.00 via addition of solid NaOH pellets, will a precipitate of “insoluble” Cd(OH)2 (Ksp = 2.5 x 10-14) fall out of solution? Prove your answer quantitatively by showing your calculations. (Assume no volume change.)
3)For each of the following “insoluble salts” state whether the solubility increases, decreases, or remains unchanged in aqueous solution upon the indicated change.
Saturated Solution of / Change / Solubility Change(increases, decreases, stays the same)
CaF2 / Addition of HNO3(aq)
NiCO3 / Addition of NiNO3(aq)
Co(OH)2 / pH increases
Cu(OH)2 / Addition of the Lewis base NH3
BaSO4 / Addition of Na2SO4
4)Tooth enamel consists of a mineral called hydroxyapatite, Ca10(PO4)6(OH)2. Briefly explain the chemistry behind the formation of tooth cavities.
Answers for Spring 2001 Solubility Equilibrium Exam Questions
1.a.1.6 x 10-4 M
b.1.3 x 10-4 M
c.6.1 x 10-12
2.IP = 8.5 x 10-14. IP > Ksp, so a precipitate of Cd(OH)2 does form.
3.
Saturated Solution of / Change / Solubility Change(increases, decreases, stays the same)
CaF2 / Addition of HNO3(aq) / Increases
NiCO3 / Addition of NiNO3(aq) / Decreases
Co(OH)2 / pH increases / Decreases
Cu(OH)2 / Addition of the Lewis base NH3 / Increases
BaSO4 / Addition of Na2SO4 / decreases
4.The chemical basis for tooth decay results from the enamel reacting with acids produced by bacteria that dwell in the mouth. Because it contains basic anions, the enamel becomes more soluble in the presence of these acids due to neutralization. As a result, cavities develop where the tooth enamel dissolves away off of the surface of the tooth. The major chemical reaction that leads to tooth decay is:
Ca10(PO4)6(OH)2(s) + 8H+(aq) 10Ca2+(aq) + 6HPO42-(aq) + 2H2O(l)
CH186
Solubility Equilibrium Exam Questions
From Spring 2001 Semester
1)A saturated solution of lanthanum fluoride, LaF3, has a F- ion concentration that is approximately equal to 2.8 x 10-5 M. Calculate the solubility product, Ksp, for this ionic compound.
2)Calculate the solubility in g/L for nickel(II) hydroxide, Ni(OH)2 (mol. wt. = 92.70 g/mol), if its solubility product, Ksp, is 6.0 x 10-16.
3)Working in Dr. Wisenheimers’s lab one day, Karla Chemie adjusted the pH of a test solution containing 0.020 M Mg2+ ion to 10.00 by addition of a small amount of base. Assuming a negligible change in volume, did a precipitate of insoluble magnesium hydroxide, Mg(OH)2 (Ksp = 5.6 x 10-12), form in Karla’s solution?
4)Predict whether the solubility of lead fluoride, PbF2, will increase, decrease, or stay about the same on addition of each of the following reagents to the saturated solution:
HNO3
NaNO3
KF
Pb(NO3)2
Answers for Fall 1999 Solubility Equilibrium Exam Questions
1.2.0 x 10-19
2.4.9 x 10-4 g/L
3.IP = 2.0 x 10-10, IP > Ksp, so a precipitate did form
4.increase
no change
decrease
decrease
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