Chemistry 1312, Exam 1
Spring, 1999

1. All of the following can be considered Brønsted bases except
a. H₂O
b. NH₃
c. HCO₃^-
d. CO₃^2-
e. all can function as a Brønsted base

2. All of the following are conjugate acid-base pairs except
a. CO₃^2-/H₂CO₃
b. NH₃/NH₄⁺
c. C₅H₅NH⁺/C₅H₅N
d. O^2-/OH^-
e. HNO₃/NO₃^-

3. K_c = 0.29 at a given temperature for 2 SO₂(g) + O₂(g) <--> 2 SO₃(g)
An experimental analysis for a 1.0-L reaction system showed the presence of 0.22 mol SO₂, 0.11 mol O₂, and 0.22 mol SO₃. Which of the following statements can be stated, based upon the analysis?
a. the chemical system is at equilibrium
b. additional SO₂ will form to reach equilibrium
c. the partial pressure of SO₃ will increase
d. the total pressure of the system will decrease
e. additional SO₃ will form to reach equilibrium

4. Calcium phosphate, Ca₃(PO₄)₂, is a slightly soluble salt, K_sp = 1.3 x 10^-32. To determine the molar solubility of Ca₃(PO₄)₂, which of the following would need to be determined?
a. the molar concentration of Ca²⁺ at equilibrium
b. the molar concentration of PO₄^3- at equilibrium
c. 1/2 the molar concentration of Ca²⁺ at equilibrium
d. 1/2 the molar concentration of PO₄^3- at equilibrium
e. none of the above

5. Lanthanum hydroxide, La(OH)₃, is a slightly soluble salt, K_sp = 1.0 x 10^-19. Which equilibrium constant expression should be used to determine the molar concentration of La3+ in a saturated La(OH)₃ solution where x = [La³⁺]?
a. K_sp = x²
b. K_sp = 9x³
c. K_sp = 27x⁴
d. K_sp = 4x⁴
e. K_sp = 108x⁵

6. Consider the dynamic equilibrium, N₂(g) + 3 H₂(g)<--> 2 NH₃(g),
DH = -92.1 kJ
All of the following favor the formation of ammonia, except
a. increasing the partial pressure of N₂
b. increasing the partial pressure of H₂
c. decreasing the volume of the reaction vessel
d. increasing the temperature of the reaction system
e. all favor the formation of NH₃

7. The K_sp for calcium hydroxide, Ca(OH)₂, is 1.6 x 10^-6. If 0.010 mol OH^- is added to 1.0-L of solution, what must be the [Ca²⁺] for a precipitate form, i.e, to form a saturated solution (dynamic equilibrium)?
a. 0.010 mol/L
b. 1.6 x 10^-2 mol/L
c. 1.6 x 10^-4 mol/L
d. 0.63 mol/L
e. none of the above

8. Which silver salt is the most soluble (has the largest molar solubility)?
a. AgCl, K_sp = 1.6 x 10^-10
b. AgBr, K_sp = 7.7 x 10^-13
c. AgI, K_sp = 1.5 x 10^-16
d. AgOH, K_sp = 1.5 x 10^-8
e. Ag₂S, K_sp = 6.3 x 10^-51

9. If for the reaction system, 2 CO(g) + O₂(g) -->  2 CO₂(g), equal concentrations of CO and O₂ were initially placed into a reaction vessel, which of the following statements is true?
a. the equilibrium concentration of O₂ will equal twice that for CO
b. the rate of decomposition of CO equals that for O₂
c. the rate of decomposition of O₂ equals the rate of formation of CO₂
d. the concentration of CO decreases to zero and the concentration of CO₂ increases to 2 mol/L
e. the equilibrium concentration of CO will equal that of O₂

10. All of the following equilibria are affected by changes in the volume of the vessel (i.e., a change in the internal pressure of the system) except
a. 2 CO(g) + O₂(g)<-->  2 CO₂(g)
b. N₂(g) + 3 H₂(g) <-->  2 NH₃(g)
c. Na₂CO₃•10H₂O(s) <-->  Na₂CO₃(s) + 10 H₂O(g)
d. CH₄(g) + 2 O₂(g)<--> CO₂(g) + 2 H₂O(l)
e. S(s) + O₂(g) <-->  SO₂(g)

11. All of the following changes could be made to increase the moles of NH3 in the equilibrium system, (an endothermic reaction) NH₄HS(s)<-->   NH₃(g) + H₂S(g), except
a. increase the amount of NH₄HS
b. increase the temperature of the system
c. decrease the amount of H₂S
d. increase the volume of the reaction vessel
e. all of the changes will increase the moles of NH₃

12. Exactly 0.20 mol of carbon monoxide gas, 0.20 mol oxygen gas, and 0.40 mol carbon dioxide gas are sealed into a 2.00 L reaction vessel. K_c = 0.66 at 2000°C for 2 CO(g) + O₂(g) <-->  2 CO₂(g)
Which of the following statements is true regarding the conditions of the system?
a. The system is at equilibrium.
b. The reaction quotient, Q_c, is greater than K_c and the reaction proceeds right to reach equilibrium.
c. The reaction quotient, Q_c, is greater than K_c and the reaction proceeds left to reach equilibrium.
d. The reaction quotient, Q_c, is less than K_c and the reaction proceeds right to reach equilibrium.
e. The reaction quotient, Q_c, is less than K_c and the reaction proceeds left to reach equilibrium.

13. The pH of a solution affects its corrosiveness on certain metals. Which of the following solutions has the highest pH?
a. 0.010 M HCl
b. 0.010 M CH₃COOH
c. 0.010 M NH₃
d. 0.010 M KOH
e. all have the same pH

14. Which of the following acidic solutions has the highest pH?
a. 0.010 M HCl
b. 0.010 M HNO₂, K_a = 4.6 x 10^-4
c. 0.010 M C₆H₅COOH, K_a = 6.3 x 10^-5
d. 0.010 M CH₃COOH, K_a = 1.8 x 10^-5
e. 0.010 M HClO, K_a = 3.0 x 10^-8

15. Only one of the following statements is always true. Which one?
a. pH + pOH = pK_w
b. for neutral water: pH = pOH = 7.0
c. [H₃O+] + [OH-] = 1.0 x 10^-14
d. [H₃O+][OH-] = 1.0 x 10^-14
e. pH + pOH = 14

16. All of the following relationships are correct at 25°C, except
a. 0.010 M HNO₃, pH = 2.0
b. 0.010 M NaOH, pOH = 2.0
c. 0.010 M H₃PO₄, pH > 2
d. 0.010 M H₂SO₄, pH > 2
e. 0.010 M Ba(OH)₂, pH > 12

1. (21 points) The Ksp of Ni(OH)₂ is 6.5 x 10^-18.
a. (5 pts) Write the equilibrium equation for the dissolution of Ni(OH)₂.
Ni(OH)₂(s) <-->  Ni²⁺(aq)   +  2 OH^-(aq)
b. (10 pts) What is the molar solubility of Ni(OH)₂?
molar solubility = 1.2 x 10^-6 mol/L
c. (6 pts) What is the pH of a saturated Ni(OH)₂ solution?
pH = 8.37

2. (10 points) Write the appropriate Brønsted equation and then determine the pH and pOH of a 0.0040 M HBr solution.
HBr(g)  +  H₂O(l)   -->  H₃O⁺(aq)  +  Br^-(aq)
pH = 2.40; pOH = 11.60

3. (14 points) a. (5 pts) Write a Brønsted equation showing phenol, C₆H₅OH, to be an acid.
C₆H₅OH(aq)  +  H₂O(l)   <-->  H₃O⁺(aq)  +  C₆H₅O^-(aq)
b. (2 pts) What is the formula for the conjugate base of phenol? _________C₆H₅O^-_____________
c. (5 pts) Write a Brønsted equation showing nicotine, C₁₀H₁₄N, to be a base.
C₁₀H₁₄N(aq)  +  H₂O(l)   <--> C₁₀H₁₄NH⁺(aq)  +  OH^-(aq)
d. (2 pts) What is the formula of the conjugate acid of nicotine? ____________C₁₀H₁₄NH⁺__________

4. (20 points) A reaction mixture of 2.00 mol CO and 3.00 mol H₂ is sealed in a 1.00 L reaction vessel and heated to 1200K. At equilibrium, 0.50 mol of CH₄ was present in the reaction system:
CO(g) + 3 H₂(g) <-->  CH₄(g) + H₂O(g)
a. (10 pts) What are the equilibrium concentrations of all substances in the system?
[CO] = 1.50 mol/L; [H₂] = 1.50 mol/L; [CH₄] = 0.50 mol/L; [H₂O] = 0.50 mol/L
b. (10 pts) What is the equilibrium constant for the system at 1200K?
K_c = 0.0494

5. (20 points) For the reaction, SO₂(g) + Cl₂(g) <-->  SO₂Cl₂(g), K_c = 89.3 at 400K. A mixture of 0.10 mol SO₂ and 0.40 mol SO₂Cl₂ is sealed into a 200 mL reaction vessel and heated to 400K. What is the expected equilibrium concentration of SO₂Cl₂?
[SO₂Cl₂] = 1.96 mol/L