CHEM 1311A FINAL EXAM PART 1B November 30, 2001
Name ______
The exam consists of 20 multiple choice questions. Each is worth 5 points. Partial credit may be granted for work shown, either computational or logical.
Please circle your choice for the correct answer.
1. A buffer solution is prepared using H2S and HS- (Ka = 9.1 x 10-8). It has [H2S] = 0.15 M and [HS-] = 0.15 M . The resulting pH will be
a. 6.86 b. 7.04 c. 8.96 d. 6.94 e. none of these
2. 80 mL of 0.75 M hydrazoic acid (HN3; Ka = 1.9 x 10-5) is titrated with 0.10 M NaOH solution. The amount of NaOH solution needed to neutralize all HN3 is
a. 250 ml b. 375 ml c. 502 ml d. 600 ml e. none of these
3. An aqueous solution of 0.10 M Na2SO4 will
a. have a pH of 7 since Na2SO4 does not hydrolyze in water.
b. have a pH less than 7 due to the formation of HSO4-.
c. have a pH greater than 7 due to the formation of KOH.
d. have a pH less than 7 due to an increase in [H3O+].
e. None of these
Accepted writing saying OH- formed or c
K1
4. If the equilibrium is rewritten as: XeF6(g) Xe(g) + 3 F2(g)
K2
Xe(g) + 3 F2(g) XeF6(g) then K2 =
a. K13 b. K1-1 c. K1 d. K11/3 e. none of these
5. When equilibrium is described as dynamic, it means that
a. the concentrations of the products are changing.
b. the concentrations of the reactants are changing.
c. Forward and reverse reactions continue to occur.
d. The ratios of products and reactants are changing.
e. Both a and b.
6. If the reaction Xe(g) + 3 F2(g) XeF6(g) is at equilibrium and the temperature is suddenly increased, the response will be
a. a shift to the right b. a shift to the left c. no change
d. insufficient data e. none of these
7. The reaction HCOOH(aq) + H2O(l) H3O+(aq) + HCOO-(aq) has Ka = 1.8 x 10-4 @ 25oC. Using the following concentrations, calculate the reaction quotient and chose the direction the reaction will proceed.
[HCOOH] = 0.10 molar [HCOO-] = 2 x 10-2 molar [H3O+] = 1 x 10-2 molar
a. 1.6 x 10-3, left b. 2.0 x 10-3, left c. 2.0 x 10-3, right d. 1.6 x 10-3, right
e. none of these
8. The [OH-] of a solution prepared by mixing 450 mL of 0.10 M HBr with 500 mL of 0.10 M KOH is
a. 5.26 x 10-7 b. 5.26 x 10-3 c. 2.35 x 10-2 d. 2.75 x 10-3
e. none of these
9. Ka for NH4+ = 5.6 x 10-10; Kb for NH3 =
a. 1.8 x 10-5 b. 1.9 x 109 c. 1.8 x 105 d. 3.6 x 10-5
e. none of these
10. For the following reaction, if the volume of the reaction vessel is increased
3 NO(g) N2O(g) + NO2(g)
Which statement is true?
a. reaction shifts right major problem with answers here; C or D or
b. yield increases written explanation accepted.
c. reaction shifts left
d. yield decreases
e. both a and b
f. both a and d
11. The ion, HCO3- is
a. part of a Brønsted-Lowrey pair b. amphoteric
c. basic in some situations d. acidic in some situations
e. all of these
12. At equilibrium, the partial pressures for the following reaction are
3 Al2Cl6(g) 2 Al3Cl9
PAl2Cl6 = 1.00 atm and PAl3Cl9 = 1.02 x 10-2atm; the equilibrium constant is
a. 1.03 x 10-3 b. 1.52 x 10-3 c. 1.04 x 10-4 d. not enough data
e. none of these
13. Ka = 6.5 x 10-5 for benzoic acid . A 0.60 molar aqueous solution will have a pH of
a. 2.1 b. 3.9 c. 4.4 d. 6.5 e. none of these
actual pH = 2.2; partial credit if 2.2 written and 2.1 chosen as answer
14. Baking soda undergoes the following equilibrium when heated:
2 NaHCO3(s) Na2CO3(s) + CO2(g) + H2O(g)
The equilibrium expression is:
a. PCO2PH2O b. [NaHCO3]/[Na2CO3]PCO2PH2O
c. [Na2CO3]PCO2PH2O/[NaHCO3] d. 1/PCO2PH2O e. none of these
15. A buffer has 0.08 moles of weak acid (Ka = 1 x 10-4) and 0.08 moles of conjugate base. When strong acid is added to the solution
a. The strong acid will not react, but will dilute the solution and reduce the pH.
b. The strong acid will neutralize the weak acid.
c. The strong acid will react with the conjugate base to give weak acid.
d. Both b and c.
e. None of these
16. For the reaction
SO2Cl2(g) SO2(g) + Cl2(g)
K = 2.4 at 100oC. At equilibrium at 100oC the partial pressures of SO2 and Cl2 are both 0.58 atm. The partial pressure of SO2Cl2 is ___ atm.
a. 0.28 b. 0.14 c. 3.6 x 10-3 d. 1.4 x 10-4 e. none of these
17. For sulfuric acid, H2SO4, Ka1 = 1 x 102. This makes sulfuric acid
a. a strong acid with Ka2 > 1 x 102 b. a strong acid with Ka2 < 1 x 102
c. a weak acid with Ka2 > 1 x 102 d. a weak acid with Ka2 < 1 x 102 e. none of these
18.
volume of titrant (ml)
19. At the equivalence point in the titration curve of question 18, the amount of titrant used is
a. 50 ml b. 25 ml c. 30 ml d. 15 ml e. none of these
20. If a reaction in a sealed vessel is at equilibrium and the pressure is suddenly increased,
a. The reaction quotient decreases.
b. the equilibrium constant decreases.
c. the reaction quotient increases.
d. the equilibrium constant increases.
e. Insufficient data.