Chem 1B
Chapter 16 Exercises
Solubility and Complex Equilibria
1.
Determine the solubility in (i) in mol/L, and (ii) in gram/L of each of the following salts:
(a) AgCl, Ksp = 1.6 x 10-10
(Answer: (i) 1.3 x 10-5 mol/L; (ii) 1.8 x 10-3 g/L)
(b) AgBr, Ksp = 5.0 x 10-13
(Answer: (i) 7.1 x 10-7 mol/L; (ii) 8.2 x 10-5 g/L)
(c) Ag2CrO4, Ksp = 9.0 x 10-12
(Answer: (i) 1.3 x 10-4 mol/L; (ii) 4.3 x 10-2 g/L)
2.
The solubility of calcium hydroxide, Ca(OH)2, in water at 25oC is 0.51 g/L. Determine the solubility
product constant (Ksp) for calcium hydroxide.
(Answer: solubility = 6.9 x 10-3 mol/L; Ksp = 1.3 x 10-6)
3.
A saturated solution of magnesium hydroxide, Mg(OH)2, has a pH = 10.42. What is the solubility of
Mg(OH)2 in mol/L? Determine the Ksp of magnesium hydroxide.
(Answer: 1.3 x 10-4 mol/L; Ksp = 9.1 x 10-12)
4.
A solution containing 0.010 M AgNO3 and 0.050 M Pb(NO3)2 is titrated with 0.050 M NaCl solution.
(a) At what concentration of Cl- AgCl begins to precipitate? PbCl2 begins to precipitate?
(b) Determine the concentration Ag+ in solution when the precipitation of PbCl2 begins.
(Answer: (a) [Cl-] = 1.6 x 10-8 M AgCl begins to ppt; (b) [Cl-] = 1.8 x 10-2 M, PbCl2 begins to ppt)
(b) If [Cl-] = 1.8 x 10-2 M, [Ag+] = 8.9 x 10-9 M)
5.
20.0 mL of 0.10 M Pb(NO3)2 solution is mixed (reacted) with 30.0 mL of 0.10 M NaCl solution. (a)
Will precipitate of PbCl2 form? (b) Determine the concentration of Pb2+ that is in equilibrium with
solid PbCl2 (Ksp = 1.6 x 10-5).
(Answer: (a) Qsp = 1.4 x 10-4 > Ksp,  ppt will form; (b) [Pb2+] = 0.010 M)
6.
Determine the solubility of AgCl (Ksp = 1.6 x 10-10) and PbCl2 (Ksp = 1.6 x 10-5), respectively, in
0.010 M NaCl solution. (Answer: AgCl = 1.6 x 10-8 mol/L; PbCl2 = 0.016 mol/L)
7.
Which of the following compounds the solubility is influenced by the pH of the solution?
Write chemical equations to show how pH will increase (or decrease) their solubility.
(a) PbCl2
(Solubility not affected by pH)
(b) PbCO3
(Solubility increases as pH decreases: PbCO3(s) ⇄ Pb2+(aq) + CO32-(aq)
CO32-(aq) + H3O+(aq) ⇄ HCO3- + H2O)
(c) CaF2
(Solubility increases as pH decreases: CaF2(s) ⇄ Ca2+(aq) + 2F-(aq)
H3O+(aq) + F-(aq) ⇄ HF + H2O)
Chem 1B
Chapter 16 Exercises
(d) Ag3PO4
(Solubility increases as pH decreases: Ag3PO4(s) ⇄ 3Ag+(aq) + PO43-(aq)
PO43-(aq) + H3O+(aq) ⇄ HPO42-(aq) + H2O)
(e) AgBr
(Solubility not influenced by pH)
8.
What is the solubility (in mol/L) of Mg(OH)2 (Ksp = 8.9 x 10-12) in a solution buffered at pH = 9.50?
(Answer: 8.9 x 10-3 mol/L)
9.
What is the solubility of silver chloride (Ksp = 1.6 x 10-10) in water and in 3.0 M NH3 solution,
respectively? [Ag+(aq) + 2NH3(aq) ⇄ Ag(NH3)2+(aq), Kf = 1.7 x 107]
(Answer: 1.3 x 10-5 mol/L in water; 0.14 mol/L in 3.0 M NH3)
10.
The solubility of which of these compounds will be greatly influenced by the formation of complex
ion (i) with NH3? (ii) with OH-? Show the equation of complex ion formation.
(a) Cr(OH)3
(Dissolves in excess OH- due to formation of Cr(OH)4- complex ion)
(b) Fe(OH)3
(Not soluble in NH3 solution; solubility decreases in excess OH-)
(c) Cu(OH)2
(Dissolves in NH3 solution due to formation of complex ion Cu(NH3)42+;
solubility decreases in excess OH-)
(d) Zn(OH)2
(Dissolves in excess OH- due to formation of complex ion Zn(OH)42- and in NH3
due to formation of complex ion Zn(NH3)62+)
(e) AgOH
(Dissolves in NH3 due to formation of complex ion Ag(NH3)2+;
Solubility decreases in excess OH-)
(f) Pb(OH)2
(Dissolves in excess OH- due to formation of complex ion Pb(OH)42-;
Not soluble in NH3)
11.
A solution contains Ag+ and Ba2+ ions. What reagents would you use to separate and extract the two
cations from the solution. Explain your choice of the reagents and the process involved.
(Answer: Add NaCl: AgCl will form ppt but BaCl2 is soluble; then add H2SO4 to ppt BaSO4)
12.
A solution contains 0.0010 M AgNO3 and 0.010 M Pb(NO3)2. Both cations may be precipitated out
from the solution by adding dilute sodium chloride or hydrochloric acid. (a) Which compound will
precipitate out first, AgCl or PbCl2? Explain. (b) What is the concentration of Ag+ when PbCl2 begins
to precipitate? (c) What is the concentration of Pb2+ when AgCl begins to precipitate? (AgCl, Ksp =
1.6 x 10-10; PbCl2, Ksp = 1.6 x 10-5)
(Answer: (a) AgCl (lower Ksp); (b) AgCl ppt when [Cl-] = 1.6 x 10-7 M; PbCl2 ppt when [Cl-] = 0.040
M; (b) When PbCl2 begins to form at [Cl-] = 0.040 M, [Ag+] = 4.0 x 10-9 M; (c) When AgCl begins to
form at [Cl-] = 1.6 x 10-7 M, [Pb2+] = 0.010 M (the original amount of Pb2+ remains in solution)
13.
In a qualitative experiment, you are given a solution that contains a mixture of the following cations:
Ag+, Ba2+, Cr3+, Fe3+, and Cu2+. Draw a flow chart to show how these cations are separated.
(Available reagents to use: 0.1 M NaCl, 0.1 M Na2SO4, 6 M HNO3, 6 M NaOH, 6 M NH3, and)