Chem 1311A Exam I a Fall 2001 s2
CHEM 1311A EXAM I B FALL 2001
Name ______
The exam consists of 25 multiple choice questions. Each is worth 4 points. Partial credit may be granted for work shown, either computational or logical.
1. The reaction 2 NO(g) + Br2(g) 2 NOBr(g) has K = 116.6 @ 25oC. Using the following partial pressures, calculate the reaction quotient and chose the direction the reaction will proceed.
PNO = 0.400 atm PBr2 = 0.105 atm PNOBr = 0.969
a. 21.3, left b. 55.9, left c. 213, right d. 55.9, right
e. none of these
2. Two buffer solutions are prepared using H2S and HS- (pKa = 7.04). The first has [H2S] = 0.26 M and [HS-] = 0.18 M with a pH of 6.88 The second has [H2S] = 0.13 M and [HS-] = 0.09 M. Its pH is
a. 7.04 b. 6.88 c. 8.96 d. 6.94 e. none of these
K1
3. If the equilibrium PCl3(g) + Cl2(g) PCl5(g) is rewritten as:
K2
1/3PCl3(g) + 1/3Cl2(g) 1/3PCl5(g) then K2 =
a. K13 b. K11/3 c. K1 d. K12 e. none of these
4. If the reaction 2 SO2(g) + O2(g) 2 SO3(g) is at equilibrium and PSO2 is suddenly decreased, the response will be
a. a shift to the right b. a shift to the left c. no change
d. unpredictable e. none of these
5. The pH of a solution prepared by mixing 40 mL of 0.10 M HBr with 50 mL of 0.10 M KOH is
a. 12.05 b. 12.75 c. 13.35 d. 13.95 e. none of these
6. Which of the following is a Brønsted-Lowrey acid-base pair?
a. H2CO3 ; CO32- b. HSO4- ; SO42- c. HCl ; NaOH d. H3PO4 ; HPO42-
e. none of these
7. Ammonia and carbon dioxide react to form ammonium carbamate with the following equilibrium:
2 NH3(g) + CO2(g) NH4OCONH2(s)
If a stoichiometric sample of the gasses is sealed in a vessel and allowed to equilibrate with the resulting solid at 25oC, the total pressure is 0.115 atm. The equilibrium constant at 25oC will be
a. 44.4 x 102 b. 33.3 x 102 c. 62.2 x 102 d. not enough data
e. none of these
8. If the pH of a 1.00 M solution of benzoic acid is 2.44, the Ka =
a. 1.3 x 10-5 b. 1.3 x 10-2 c. 2.3 x 10-2 d. 2.3 x 10-5 e. none of these
9. A solution of 0.600 mol of formic acid (Ka = 1.8 x 10-4) and 0.500 mol sodium formate in 500 mL of water is prepared. The equilibrium H3O+ concentration is
a. 1.35 x 10-4 b. 1.35 x 10-6 c. 2.16 x 10-4 d. 2.40 x 10-5
e. none of these
10. 50 mL of 0.50 M hydrazoic acid (HN3; Ka = 1.9 x 10-5) is titrated with 0.10 M NaOH solution. The pH before any base is added is
a. 5.72 b. 6.86 c. 2.51 d. 2.86 e. none of these
11. The following reaction is exothermic:
3 NO(g) N2O(g) + NO2(g)
Which statement is true?
a. as temperature is increased, reaction shifts right
b. as pressure is increased, reaction shifts left
c. as temperature is increased, reaction shifts left
d. as volume is increased, reaction shifts right
e. none of the above
12. The equilibrium expression for the following reaction:
H2O(l) + Cl2(g) + C(s) COCl2(g) + H2(g)
is
a. PCl2 / PCOCl2PH2 b. PCOCl2PH2/PCl2
c. PCOCl2PH2/ [C][H2O]PCl2 d. [C][H2O]PCl2 / PCOCl2PH2 e. none of these
13. A solution of 0.05 M NaF will
a. have a pH less than 7 due to the formation of HF.
b. have a pH of 7 since NaF does not react with water.
c. have a pH greater than 7 due to the formation of HF.
d. have a pH less than 7 due to an increase in [H3O+].
e. None of these
14. 0.01 moles of strong acid is added to a buffer of 0.10 moles of weak acid (Ka = 1 x 10-4) and 0.08 moles of conjugate base. The resulting solution will have
a. 0.09 moles of weak acid and 0.09 moles of conjugate base.
b. 0.11 moles of weak acid and 0.09 moles of conjugate base.
c. 0.11 moles of weak acid and 0.07 moles of conjugate base.
d. 0.01 moles of strong acid and 0.09 moles of weak acid.
e. None of these
15. A saturated solution of benzoic acid in water has a concentration of 0.016 M. At the same temperature a saturated solution of benzoic acid in diethyl ether has a concentration of 5.41 M. The partition coefficient for the reaction
benzoic acid (ether) benzoic acid (aq)
is
a. 2.96 x 10-3 b. 5.91 x 10-3 c. 440 d. 320 e. none of these
16. For the reaction
CO(g) + Cl2(g) COCl2(g)
K = 0.20 at 600oC. At equilibrium at 600oC the partial pressures of CO and COCl2 are 0.025 and 1.8 x 10-5 respectively. The partial pressure of Cl2 is
a. 3.1 x 10-3 b. 1.44 x 10-4 c. 3.6 x 10-3 d. 2.5 x 10-2 e. none of these
17. For carbonic acid, H2CO3, Ka2 = 4.8 x 10-11. Therefore, Ka1 is
a. 2.4 x 10-11 b. less than 4.8 x 10-11 c. greater than 4.8 x 10-11 d. 4.3 x 10-2
e. none of these
18.
This curve represents a titration of a
a. strong acid with a strong base.
b. strong base with a strong acid.
c. weak acid with a strong base.
d. weak base with a strong acid.
e. strong base with a salt.
19. On the curve in question 18 the point where pH » pKa of the starting material is labeled
a. A b. B c. C d. D e. E
20. As equilibrium in a chemical reaction is approached,
a. the rate of the forward reaction approaches zero.
b. the rates of both the forward and the reverse reactions approach the same value
c. the rate of the reverse reaction approaches zero.
d. Both a and c are correct.
e. None of these
21. The value of the equilibrium constant for a particular chemical reaction is dependent upon
a. the initial amounts of reactants.
b. the final pressure of the reaction vessel.
c. the temperature of the reaction vessel.
d. a, b, and c
e. none of these
22. Which of the following ions can be considered amphoteric?
a. F- b. H+ c. PO43- d. HCO3- e. none of these
23. Which of the following Ka values belong to the weakest acid?
a. 6.6 x 10-4 b. 4.6 x 10-4 c. 9.1 x 10-8 d. 3.0 x 10-8
e. there is insufficient data
24. When considering the titration in problem 19, the most appropriate indicator would be ___ with its color changing over the pH range ____.
a. Thymol blue; 8.0 – 9.6 b. alizarin yellow; 10.1 - 12.0
c. methyl red; 4.8 – 6.0 d. cresol red; 7.0 – 8.8
e. phenolphthalein; 8.2 – 10.0
25. HCl, HBr, and HI are all strong acids while HF is a weak acid. This can be explained by:
a. The HF bond is more ionic than the others.
b. HCl, HBr, and HI all effectively dissociate 100% in water.
c. The high electronegativity of F inhibits the dissociation of HF in water.
d. Both b and c.
e. None of the above