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Chem 126 Common 2 March 7, 2008 Dr. Ellis

NONE OF THE MULTIPLE CHOICE PROBLEMS REQUIRES EXTENSIVE OR TIME COMSUMING CALCULATIONS. IF YOUR METHOD REQUIRES EXTENSTIVE CALCULATIONS IT IS EITHER WRONG OR HARDER THAN WHAT IS REQUIRED. 1. What is the equilibrium constant for the reaction: 2 ( ) ( ) 3C(g)+D(s)A s B g+ ⇌ , given that in a 5.00 L

container A = 0.35 moles, B = 0.20 moles, C = 0.25 moles, and D = 0.21 moles at equilibrium?

(a) 0.13 M2 (b) 0.027 M2 (c) 1.25 M2 (d) 0.39 M2 (e) 0.0031 M2

2. Some silicon dioxide, water, silane (SiH4), and oxygen are at equilibrium in a sealed container at a particular

temperature: ( ) ( ) ( ) ( )2 2 4 22 2 0SiO s H O g SiH g O g H+ + ∆ >⇌ In which of the following cases does the reaction NOT proceed to right to reestablish equilibrium?

(a) Some silicon dioxide is added. (b) Some water vapor is added. (c) Some oxygen is removed. (d) The temperature is increased. (e) The volume of the container is increased.

3. All of the following compounds are soluble in water and are strong electrolytes except

(a) NaI. (b) PbI2. (c) Ca(CH3COO)2. (d) NH4CH3COO. (e) MgCl2.

4. The concentration of an HCl solution is 0.25 M. What is the pH?

(a) -1.38 (b) -0.60 (c) 0 (d) 0.60 (e) 1.38

5. 5.60 g of HI is dissolved in enough water to make a 0.200 L solution. What is the pH?

(a) -0.75 (b) -1.45 (c) 1.52 (d) 0.75 (e) 0.66

6. Calculate the pH of a 4.43 x 10-5 M barium hydroxide, Ba(OH)2, solution.

(a) 4.05 (b) 9.95 (c) 4.35 (d) 9.65 (e) none of the above

Chem 126 Common 2 March 7, 2008 Dr. Ellis

7. The pOH of a NaOH solution is 4.77. What is the concentration of the OH- ion?

(a) 0.00848 M (b) 5.89x10-10 M (c) 3.40 x 10-5 M (d) 0.00424 M (e) 1.70x10-5 M

8. What is the pH of a solution formed by mixing 35.0 mL of 0.66 M HNO3 and 115 mL of 0.250 M KOH?

(a) 1.42 (b) 12.69 (c) 12.58 (d) 13.21 (e) none of the above

9. A solution consists of 0.75 M phenol (C6H5OH, a weak acid, with Ka = 1.0 x10-10 M) and 0.040 M HNO3.

What is the pH?

(a) 1.40 (b) 0.125 (c) 0.10 (d) 1.30 (e) none of the above 10. A 3.6x10-4 M aqueous solution of a weak acid, HB, has a pH of 6.03. Calculate Ka, the acid-dissociation

constant, for HB. (HB is some unknown weak acid. Its actual composition is irrelevant for solving the problem.)

(a) 2.6x10-3 M

(b) 5.7x10-7 M

(c) 6.0x10-5 M

(d) 2.4x10-9 M

(e) none of the above

11. Which of the following solutions is neutral?

(a) CH3NH2(aq) (b) CsI(aq) (c) KCH3COO(aq) (d) HCOOH(aq) (e) FeCl3(aq)

Chem 126 Common 2 March 7, 2008 Dr. Ellis

12. For the reaction: ( ) ( ) ( ) ( )3 3 4 3aq aq aq + aqNH CH COOH NH CH COO+ −+ " , what is the conjugate base?

(a) NH3 (b) CH3COOH (c) NH4+ (d) CH3COO- (e) OH-

13. Which of the following solutions has the highest solubility for iron (III) hydroxide?

(a) pure water

(b) water buffered to a pH of 2

(c) water buffered to a pH of 5

(d) water buffered to a pH of 10

(e) water buffered to a pH of 12

14. What is the concentration of a 5.00 L HBr solution if 30.0 mL of it is completely neutralized by 95.7 mL

0.25 M NaOH? (a) 0.798 M

(b) 0.754 M

(c) 0.250 M

(d) 0.190 M

(e) 0.0479 M

15. In which of the following reactions does the underlined compound act as a Lewis base?

( ) ( ) ( ) ( )

( ) ( ) ( ) ( )

( ) ( )

4

4

3 2

2 3 3

3 33 3

.

.

. where the N is bonded to the Ga

I NH aq H O l NH aq OH aq

II NH aq H O l NH aq H O aq

III NH Ga OH NH Ga OH

+ −

+ +

+ +

+ +

+

⇌

⇌

⇌

(a) only I (b) only II (c) only III (d) II and III (e) I, II, and III

16. Calculate the pH of a solution that is 0.21 M in HF and 1.43 M KF.

(HF: Ka = 6.76 x 10-4 M) (a) 0.68 (b) 1.92 (c) 4.00 (d) 3.17 (e) 2.34

Chem 126 Spring 2007 Common 2 March 9 Dr. Ellis

PROBLEMS (12 points each; 36 total) I. The Ka for Chlorous acid, HClO2, is 1.15 x 10-2 M.

(a) (4 PT) What is the [H+] for a 0.85 M solution of this acid? Show work, including an ICE table. Use method of successive approximation for full credit. ( ) ( ) ( )2 2HClO aq H aq ClO aq+ −+⇌

(b) (4 PT) What is the percent dissociation of chlorous acid?

(c) (4 PT) What happens to the percent dissociation as the solution of chlorous acid is diluted by the addition of water? Why? (Circle correct choice and give reason.)

-It decrease because ______________________________________________________

-It stays the same because _____________________________________________________

-It increases because _____________________________________________________

Chem 126 Spring 2007 Common 2 March 9 Dr. Ellis

II. Separation of ions by precipitation. A solution contains 0.30 M AgNO3 and 0.50 M Ca(ClO4)2.

Sodium carbonate will be added to the solution. The Ksp for silver carbonate is 8.5 x 10-12 M3. The Ksp

for calcium carbonate is 5 x 10-9 M2.

(a) (2 PT) Write the equation for the dissolution of Ag2CO3, (Include (s) and (aq) and charge on ions)

(b) (2 PT) Write the solubility product expression for the dissolution of silver carbonate (Ksp = ?):

(c) (2 PT) At what carbonate concentration does silver carbonate start to precipitate?

(d) (2 PT) At what carbonate concentration does calcium carbonate start to precipitate? Hint, first do

steps (a) and (b) above.

(e) (2 PT) As the carbonate ion concentration increases, what compound is the first to precipitate? Why?

(f) (2 PT) For the compound which precipitates first, what is the concentration of its remaining ions

when the second compound begins to precipitate?

Chem 126 Spring 2007 Common 2 March 9 Dr. Ellis

III (a) (6 PT) What is the pH of a 0.444 M potassium cyanide, KCN, solution? For HCN, the Ka is 4.79 x 10-10 M. Include (i) writing the reaction (the net ionic reaction, that is, what takes place when KCN is added to water), (ii) finding the value of its equilibrium constant (Kb), and (iii) setting up the ICE table. (b) (6 PT) What is the solubility of copper (II) phosphate in a 0.35 M solution of Cu(NO3)2. The Ksp is 1.4 x 10-37 M5. Include (i) writing the reaction for the dissolution of copper (II) phosphate, (ii) setting up an ICE table, and (iii) writing the solubility product expression (Ksp = ?).