I. Multiple Choice (90 points) Select the best response for each of the following and record on the Scantron. Do not erase; erasures may result in a misgrading of your response.
1. Consider the following system at a dynamic equilibrium:
CH4(g) + 2 O2(g) <--> CO2(g) + 2 H2O(l) DH° = –890 kJ
An increase in the partial pressure of CO2(g) causes all of the following to exist once equilibrium is re-established except
a. the temperature has increased
b. the partial pressure of CH4(g) has increased
c. the partial pressure of CO2(g) has increased
d. the partial pressure of O2(g) has increased
e. the amount of H2O(l) has decreased2. All of the following are conjugate acid-base pairs except
a. CO32-/HCO3-
b. NH3/NH4+
c. C5H5NH+/C5H5N
d. H3O+/OH-
e. HNO3/NO3-3. Consider the reaction: 2 SO2(g) + O2(g) <--> 2 SO3(g). If A moles of SO2 and B moles of O2 are placed into a 1.00 L reaction vessel and x moles of SO3 are present at equilibrium, what is the equilibrium expression for the reaction?
a. Kc = (formulas not available)
b. Kc =
c. Kc =
d. Kc =
e. Kc =4. Exactly 0.400 mol each of carbon monoxide gas, chlorine gas, and carbonyl chloride gas are sealed into a 0.770 L reaction vessel. Kc = 7.52 at 919 °C for CO(g) + Cl2(g) <--> COCl2(g)
Which of the following statements is true regarding the conditions of the system?
a. The system is at equilibrium.
b. The reaction quotient, Qc, is greater than Kc and the reaction proceeds right to reach equilibrium.
c. The reaction quotient, Qc, is greater than Kc and the reaction proceeds left to reach equilibrium.
d. The reaction quotient, Qc, is less than Kc and the reaction proceeds right to reach equilibrium.
e. The reaction quotient, Qc, is less than Kc and the reaction proceeds left to reach equilibrium.5. Which of the following salts has the greatest molar solubility (most soluble) in an aqueous solution?
a. AgI, Ksp = 8.5 x 10-17
b. AgCl, Ksp = 1.8 x 10-10
c. PbCO3, Ksp = 3.3 x 10-14
d. HgI2, Ksp = 2.8 x 10-29
e. BaSO4, Ksp = 8.7 x 10-116. What species (exclusive of water) are present in a saturated solution of Ca3(PO4)2 solution? Ca3(PO4)2 is a slightly soluble salt.
a. Ca3(PO4)2(aq) and Ca2+(aq)
b. Ca2+(aq) and PO43-(aq) in a 1:1 mole ratio
c. Ca2+(aq) and PO43-(aq) in a 2:3 mole ratio
d. Ca3(PO4)2(aq), Ca2+(aq), PO43-(aq)
e. Ca2+(aq) and PO43-(aq) in a 3:2 mole ratio7. All of the following substances contain only ions in dilute aqueous solutions except
a. AgNO3
b. CH3NH2
c. KOH
d. HCl
e. H2SO48. Consider the following system at a dynamic equilibrium:
Cl2(g) + H2O(g) <--> 2 HCl(g) + O2(g)
All of the following stresses on the system results in an increase in the equilibrium concentration of O2(g) except
a. decrease the partial pressure of HCl(g)
b. increase the partial pressure of Cl2(g)
c. increase the volume of the reaction vessel
d. increase the Kc by a temperature adjustment
e. all increase the partial pressure of O2(g)9. Which of the following solutions has a pH nearest to 7.00 at 25°C?
a. 0.010 M Ba(OH)2
b. 0.010 M KOH
c. 0.010 M HClO
d. 0.010 M HCl
e. 0.010 M H2SO410. Lanthanum(III) iodate, La(IO3)3, has a Ksp of 6.1 x 10-12 at 25°C. What is the correct mass action expression to use for determining the solubility of lanthanum(III) iodate? Assume "x" to equal the solubility of lanthanum(III) iodate.
a. Ksp = 3x3
b. Ksp = 27x4
c. Ksp = x2
d. Ksp = 3x4
e. none of the above11. The pH of a citric acid solution is 4.2. Which of the following expressions is true at 25°C?
a. pH = pOH = 4.2
b. [OH-] = 9.8
c. [H3O+] = 6.3 x 10-5 mol/L
d. [H3O+] = 1.6 x 104 mol/L
e. none of the above12. At 222°C, the equilibrium partial pressure of NH3 is 0.40 atm, of N2 is 0.20 atm, and of H2 is 0.60 atm.
2 NH3(g) <--> N2(g) + 3 H2(g)
By means of a "cold trap" ammonia gas is removed until its equilibrium partial pressure is 0.10 atm. As a consequence of this change,
a. the position of equilibrium shifts to the right
b. the position of equilibrium will be unaffected
c. the DHrxn for the reaction as written must be negative
d. the value of the equilibrium constant will increase
e. the partial pressure of H2 will decrease13. Which of the following bases has the highest pH?
a. 0.010 M NaOH
b. 0.010 M NH2OH, Kb = 1.1 x 10-8
c. 0.010 M N2H4, Kb = 1.7 x 10-6
d. 0.010 M C5H5H, Kb = 1.8 x 10-9
e. since all are bases, none have a pH value14. What true statement can be made regarding a 0.0100 M HCN (hydrocyanic acid) solution at equilibrium?
a. the pH of the solution is < 2
b. the pH of the solution = 2
c. the species in highest concentration is H3O+
d. [CN-] = [H3O+]
e. [H3O+] = 0.010 mol/L15. What is the pH of blood?
a. 1.5
b. 3.98 x 10-8
c. 6.6
d. 7.0
e. 7.416. Consider the gaseous equilibrium, HQv(g) + Rx(g) <--> HRx(g) + Qv(g). If equal molar concentrations of all substances are placed in a reaction vessel and the equilibrium constant Kc<<1, then which of the following statements is true?
a. the equilibrium partial pressure of HQv > HRx
b. HRx is a weak proton donor
c. the equilibrium partial pressure of Rx is negligible
d. Rx is a strong proton acceptor
e. the equilibrium partial pressure of HRx << Qv
II. Exercises. (75 points) All work must be shown clearly and legibly in order to receive credit. Answers, without a logical presentation, will receive only 10% credit.
1. (15 points) The equilibrium constant, Kc, is 3.0 at a given temperature for
NOCl2(g) <--> NO(g) + Cl2(g)
A 1.32 mol sample of NOCl2(g) is placed into a 3.00 L reaction vessel and heated until equilibrium is established. What is the equilibrium molar concentration of NOCl2(g) ?
[NOCl2] = 0.050 mol/L2. (20 points) A chemical reaction of mixture of 0.200 mol SO2(g) and 0.400 mol O2(g) is placed into a 4.00 L reaction vessel. The reaction mixture is heated to a temperature at which the equilibrium concentration of SO2(g) is determined to be 0.0300 mol/L.
2 SO2(g) + O2(g) <--> 2 SO3(g)
a. (10 pts) What are the equilibrium molar concentrations of O2(g) and SO3(g) ?
[O2] = 0.090 mol/L
[SO3] = 0.020 mol/L
b. (10 pts) What is Kc for the reaction at this temperature?
Kc = 4.943. (15 points) A 0.00700 mol amount of HI is dissolved to form 250 mL of an aqueous solution. a. (10 pts) What is the pH of the resulting solution?
pH = 1.55
b. (5 pts) What is the percent ionization of HI in solution?
100% (strong acid)4. (25 points) A 0.00700 mol amount of HIO is dissolved to form 250 mL of an aqueous solution. Ka for HIO is 2.3 x 10-11
a. (10 pts) What is the pH of the resulting solution?
pH = 6.10
b. (5 pts) What is the percent ionization of HIO in solution?
2.87 x 10-3 %
c. (10 pts) The above (Exercise 4) solution is diluted to 7.00 L. What now is the percent ionization of HIO in solution?
1.52 x 10-2 %