Chemistry 12 – Solubility Equilibrium Unit Test



Chemistry 12 – Solubility Equilibrium Unit Test / 71 marks

Multiple Choice Section: Choose the best answer. (16 marks)

1. Molecular solutions do not conduct electricity because they contain:

a) molecules only

b) cations and anions

c) molecules and anions

d) molecules and cations

2. To determine the solubility of a solute in water, a solution must be prepared that is:

a) saturated

b) unsaturated

c) concentrated

d) supersaturated

3. From the list of salts below, how many are considered soluble at 25°C?

CuCl2 CaSO4 PbS Ag3PO4

a) none

b) one

c) two

d) three

4. Consider the following equilibrium:

NH4Cl (s) (( NH4+ (aq) + Cl- (aq) ΔH = positive

Which of the following will increase the solubility of ammonium chloride?

a) stirring the solution

b) adding water

c) adding NH4Cl

d) heating the solution

5. Na2SO4 solution is slowly added to a solution which contains 0.10 M Ba2+ and 0.10 M Pb2+. Which of the following statements describes the result of the addition of Na2SO4?

a) BaSO4 precipitates first because it is more soluble.

b) PbSO4 precipitates first because it is more soluble.

c) BaSO4 precipitates first because it is less soluble.

d) PbSO4 precipitates first because it is less soluble.

6. Identify the most soluble sulphide.

a) HgS Ksp = 1.6 x 10-54

b) PbS Ksp = 7.0 x 10-29

c) FeS Ksp = 3.7 x 10-19

d) MnS Ksp = 2.3 x 10-13

7. Four samples of a solution were analyzed and the following data were collected:

Anion added Observation

S2- nothing

SO42- precipitate

OH- nothing

CO32- precipitate

Which one of the following Group II cations is found in the unknown solution?

a) Mg2+

b) Ca2+

c) Sr2+

d) Ba2+

8. The [OH-] is measured to be 3.3 x 10-3 mol/L in a 100 mL sample of a saturated solution of Al(OH)3. What is the solubility of Al(OH)3?

a) 1.1 x 10-4 mol/L

b) 3.3 x 10-4 mol/L

c) 1.1 x 10-3 mol/L

d) 3.3 x 10-3 mol/L

9. Which of the following salts has the lowest solubility?

a) Copper (I) chloride

b) Ammonium sulphide

c) Potassium hydroxide

d) Mercury (II) sulphate

10. The mixture that could produce a precipitate of two compounds is:

a) HgSO4 and FeCl2

b) AgNO3 and MgCl2

c) K2CO3 and CuSO4

d) ZnSO4 and Ba(OH)2

11. In a saturated solution of zinc hydroxide, at 40°C, the [Zn2+] = 1.8 x 10-5 M. What is

the Ksp of the compound?

a) 5.8 x 10-15

b) 2.3 x 10-14

c) 1.8 x 10-14

d) 6.5 x 10-10

12. When equal volumes of 0.060 M AgNO3 and 0.00090 M Ba(BrO3)2 are mixed, the trial

ion product is:

a) Less than Ksp and a precipitate forms.

b) Greater than Ksp and a precipitate forms.

c) Less than Ksp and no precipitate forms.

d) Greater than Ksp and no precipitate forms.

13. What is the maximum amount of sodium sulphate that will dissolve in 1.0 L of 0.10 M

Pb(NO3)2 without forming a precipitate?

a) 1.8 x 10-8 mol

b) 1.8 x 10-7 mol

c) 1.3 x 10-4 mol

d) 1.0 x 10-1 mol

14. Which one of the following equilibrium systems is described by a Ksp?

a) CaCO3 (s) (( CaO (s) + CO2 (g)

b) CaCO3 (s) (( Ca2+ (aq) + CO32- (aq)

c) Ca2+ (aq) + CO32- (aq) (( CaCO3 (s)

d) Ca(OH)2 (aq) + H2CO3 (aq) (( CaCO3 (s) + 2H2O (l)

15. In an experiment, a student mixes equal volumes of 0.0020 M Pb2+ ions with 0.0040 M I-

ions. What is the trial ion product?

a) 4.0 x 10-9

b) 3.2 x 10-8

c) 1.3 x 10-7

d) 8.0 x 10-6

16. A 0.50 L solution of CuBr2 contains 0.30 mol Br- ions. What are the ionic

concentrations in the solution?

a) [Cu2+] = 0.15 M [Br-] = 0.30 M

b) [Cu2+] = 0.30 M [Br-] = 0.60 M

c) [Cu2+] = 0.60 M [Br-] = 0.60 M

d) [Cu2+] = 0.60 M [Br-] = 1.20 M

Written Section: Answer the following questions showing all your work! (55 marks)

1. Write an equation that describes the equilibrium present in a saturated solution of Cu3PO4. (1 mark)

2. 53 g of Na2CO3 are dissolved in sufficient water to make 5.0 L of solution.

a) Write the equation for the dissolution of Na2CO3 into its aqueous ions. (1 mark)

b) Calculate the concentration of each ion in solution. (3 marks)

c) Describe the change in entropy as the Na2CO3 dissolves. (1 mark)

3. Write an equilibrium equation and a Ksp expression for only those salts that have low solubility: (5 marks)

a) Cu2S

b) PbI2

c) Al2(SO4)3

4. A 1.0 M solution of sodium sulphide is added to a 1.0 M solution of copper (II) chloride resulting in the formation of a precipitate.

a) Write the formula of the precipitate. (1 mark)

b) Write the formula equation for the reaction. (1 mark)

c) Write the net ionic equation for the reaction. (1 mark)

5. Calculate the concentration of each ion in the following saturated solutions: (12 marks)

a) Al(OH)3 Ksp = 3.0 x 10-33

b) Pb(IO3)2 Ksp = 3.7 x 10-13

6. A suspension of barium sulphate is used to improve the quality of X-rays in the digestive system. If the patient is required to drink 0.400 L of this suspension, calculate the actual mass in grams of the dissolved BaSO4. (5 marks)

7. Calculate the Ksp for Mg(OH)2 if the solubility of Mg(OH)2 is 7.6 mg/L. (5 marks)

8. What maximum [F-] exists in a solution in which the [Sr2+] = 4.4 x 10-3 M? (4 marks)

9. Show by calculation if a precipitate forms when 10.0 mL of 0.010 M AgNO3 are mixed with an equal volume of 0.10 M Na2CO3. (5 marks)

10. A solution may contain Ba2+ and/or Al3+ ions. Describe a procedure to confirm the presence or absence of these ions. (4 marks)

11. A 25.0 mL sample of saturated PbCl2 solution is titrated to the endpoint with 48.1 mL of 0.015 M AgNO3 solution. Calculate the Ksp of PbCl2. (6 marks)

Multiple Choice Answers:

1. a 5. c 9. a 13. b

2. a 6. d 10. d 14. b

3. b 7. c 11. b 15. a

4. d 8. c 12. c 16. b

Written Answers:

1. Cu3PO4 (s) (( 3Cu+ (aq) + PO43- (aq)

2. a) Na2CO3(s) ( 2Na+ (aq) + CO32- (aq)

b) Molar Mass Na2CO3 = 106.0 g / mol.

[Na2CO3] = 53 g x (1 mol / 106.0 g) x (1 / 5.0 L) = 0.10 M

[Na+] = 2 x 0.10 M = 0.20 M

[CO32-] = 0.10 M

c) Entropy increases as ions are formed.

3. a) Cu2S (s) (( 2Cu+ + S2- Ksp = [Cu+]2 [S2-]

b) PbI2 (s) (( Pb2+ + 2I- Ksp = [Pb2+] [I-]2

c) Soluble (Therefore, no rxn)

4. a) CuS

b) Na2S (aq) + CuCl2 (aq) ( CuS (s) + 2NaCl (aq)

c) Cu2+ (aq) + S2- (aq) ( CuS (s)

5. a) Al(OH)3 (s) ( Al3+ + 3OH-

x 3x Let x = [Al3+] ; 3x = [OH-]

Ksp = [Al3+] [OH-]3 = x (27x3) = 27x4 = 3.0 x 10-33

x = 3.25 x 10-9 M

Therefore, [Al3+] = x = 3.3 x 10-9 M and [OH-] = 3x = 9.7 x 10-9 M.

b) Pb(IO3)2 (s) ( Pb2+ + 2IO3-

x 2x Let x = [Pb2+] ; 2x = [IO3-]

Ksp = [Pb2+] [IO3-]2 = x (4x2) = 4x3 = 3.7 x 10-13

x = 4.52 x 10-5 M

Therefore, [Pb2+] = x = 4.5 x 10-5 M and [IO3-] = 2x = 9.0 x 10-5 M.

6. BaSO4 (s) ( Ba2+ + SO42-

x x x Let x = solubility of BaSO4 = [Ba2+] = [SO42-]

Ksp = [Ba2+] [SO42-] = x2 = 1.1 x 10-10

x = 1.05 x 10-5 M

Molar mass BaSO4 = 233.4 g / mol

Mass BaSO4 = 1.05 x 10-5 mol / L x 0.400 L x (233.4 g / 1 mol) = 9.8 x 10-4 g.

7. Mg(OH)2 (s) ( Mg2+ + 2OH-

x x 2x Let x = solubility of Mg(OH)2 = [Mg2+]; 2x = [OH-]

Molar mass Mg(OH)2 = 58.3 g / mol

Mass Mg(OH)2 = 7.6 mg / L x (1 g / 1000 mg) x (1 mol / 58.3 g) = 1.30 x 10-4 M

[Mg2+] = x = 1.30 x 10-4 M

[OH-] = 2x = 2.61 x 10-4 M

Ksp = [Mg2+] [OH-]2 = (1.30 x 10-4 M) (2.61 x 10-4 M)2 = 8.8 x 10-12

8. SrF2 (s) (( Sr2+ + 2F-

Ksp = [Sr2+] [F-]2 = [4.4 x 10-3] [F-]2 = 4.3 x 10-9

[F-] = 9.9 x 10-4 M

9. Dilution calculations required!

[Ag+] = (10.0 mL x 0.010 M) / 20.0 mL = 0.0050 M

[CO32-] = (10.0 mL x 0.010 M) / 20.0 mL = 0.0050 M

Ag2CO3 (s) (( 2Ag+ + CO32-

Ksp = [Ag+]2 [CO32-] = 8.5 x 10-12

Q = [Ag+]2 [CO32-] = (0.0050)2 (0.0050) = 1.25 x 10-6

Q > Ksp (Therefore, a ppt forms!)

10. Multiple answers exist. A possible answer:

Step 1: Add Na2SO4 to ppt out Ba2+ as BaSO4. Filter if ppt forms.

Step 2: Add Na2SO3 to ppt out Al3+ as Al2(SO3)3. Filter if ppt forms.

11. Moles of Ag+ added = 0.0481 L x 0.015 mol / L = 0.000722 mol Ag+

Moles of Ag+ = moles of Cl- in solution

[Cl-] = (0.000722 mol) / 0.0250 L = 2.89 x 10-2 M

PbCl2 (s) (( Pb2+ + 2Cl-

[Pb2+] = 0.5 x [Cl-] = 0.5 x (2.89 x 10-2 M) = 1.44 x 10-2 M

Ksp = [Pb2+] [Cl-]2 = (1.44 x 10-2 M) (2.89 x 10-2 M)2 = 1.2 x 10-5

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