Chem1120pretest2Summeri2015

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Chem1120pretest2Summeri2015 Multiple Choice Identify the choice that best completes the statement or answers the question. 1. When the system A + B C + D is at equilibrium, a. the forward reaction has stopped. b. the reverse reaction has stopped. c. both the forward and the reverse reactions have stopped. d. neither the forward nor the reverse reaction has stopped. e. the sum of the concentrations of A and B must equal the sum of the concentrations of C and D. 2. Consider the gas phase system below at a high temperature. The form of the expression for the equilibrium constant, K c,. 4NH 3 + 5O 2 4NO + 6H 2 O a. cannot be determined without rate data b. c. is d. e. is is is 3. For a reversible reaction with a one-step mechanism, A B, the rate of the forward reaction is rate f = 3.2 10 6 s 1 [A] and the rate of the reverse reaction is rate r = 4.6 10 4 s 1 [B]. What is the value of K c for this reaction? a. 2.5 10 11 b. 7.0 10 9 c. 7.0 10 3 d. 1.4 10 2 e. 1.5 10 9 4. At equilibrium, the following amounts are found at a certain temperature in a 3.0-liter container: 2.0 mole of Cl 2, 0.80 mol of H 2 O (steam), 0.0030 mol of HCl, and 0.0045 mol of O 2. Evaluate K c at that temperature. 2Cl 2 (g) + 2H 2 O(g) 4HCl(g) + O 2 (g) a. 4.7 10 14 b. 8.4 10 7 c. 1.4 10 13 d. 2.2 10 13

e. 7.1 10 12 5. The equilibrium constant for the following gas phase reaction is 0.50 at 600 C. A mixture of HCHO, H 2, and CO is introduced into a flask at 600 C. After a short time, analysis of a small amount of the reaction mixture shows the concentrations to be [HCHO] = 1.5 M, [H 2 ] = 0.5 M, and [CO] = 1.0 M. Which of the following statements about this reaction mixture is true? HCHO H 2 + CO a. The reaction mixture is at equilibrium. b. The reaction mixture is not at equilibrium, but no further reaction will occur. c. The reaction mixture is not at equilibrium, but will move toward equilibrium by forming more HCHO. d. The reaction mixture is not at equilibrium, but will move toward equilibrium by using up more HCHO. e. The forward rate of this reaction is the same as the reverse rate. 6. The equilibrium constant, K c, is 0.022 at 25 C for the reaction below. What is the concentration of PCl 5 at equilibrium if a reaction is initiated with 0.80 mole of PCl 5 in a 1.00-liter container? PCl 5 (g) PCl 3 (g) + Cl 2 (g) a. 0.080 M b. 0.12 M c. 0.54 M d. 0.68 M e. 0.76 M 7. For the following system at equilibrium, H 2 (g) + CO 2 (g) H 2 O(g) + CO(g) the addition of H 2 (g) would cause (according to LeChatelier's principle) a. only more H 2 O(g) to form. b. only more CO(g) to form. c. more H 2 O(g) and CO(g) to form. d. only more CO 2 (g) to form. e. no change in amounts of products or reactants. 8. Suppose we let the reaction below come to equilibrium. Then we decrease the total pressure, by increasing the volume of the container. What will be the effect on the net amount of SO 3 (g) present? 2SO 2 (g) + O 2 (g) 2SO 3 (g) a. It increases. b. It decreases. c. It does not change. d. The question cannot be answered without knowing the value of K. e. The question cannot be answered without knowing the value of H 0. 9. For the gas phase reaction below, H 0 = 1.6 10 2 kj for the forward reaction. SO 2 + O 2 SO 3 In order to increase the yield of SO 3, the reaction should be run a. at high P, high T.

b. at high P, low T. c. at low P, high T. d. at low P, low T. e. at high P, but is independent of T. 10. A Brønsted-Lowry acid is defined as a. a. species that donates a proton b. species that accepts a proton c. species that accepts a share in an electron pair d. species that makes available a share in an electron pair e. species that produces H + ions in aqueous solution Chapter 18 Values The following values will be useful for the problems in this chapter. Acid K Substance or Species K HF K a = 7.2 10 4 NH 3 K b = 1.8 10 5 HNO 2 K a = 4.5 10 4 (CH 3 ) 3 N K b = 7.4 10 5 CH 3 COOH K a = 1.8 10 5 [Co(OH 2 ) 6 ] 2+ K a = 5.0 10 10 HOCl K a = 3.5 10 8 [Fe(OH 2 ) 6 ] 2+ K a = 3.0 10 10 HOBr K a = 2.5 10 9 [Fe(OH 2 ) 6 ] 3+ K a = 4.0 10 3 HOCN K a = 3.5 10 4 [Be(OH 2 ) 4 ] 2+ K a = 1.0 10 5 HCN K a = 4.0 10 10 [Cu(OH 2 ) 4 ] 2+ K a = 1.0 10 8 H 2 SO 4 K a1 = very large HBO 2 K a = 6.0 10 10 K a2 = 1.2 10 2 (COOH) 2 K a1 = 5.9 10 2 H 2 CO 3 K a1 = 4.2 10 7 K a2 = 6.4 10 5 11. Of the following, which acids are weak acids? I. HBr II. HF III. HNO 3 IV. HNO 2 V. H 2 CO 3 VI. H 3 PO 4 a. I, II, and III b. II, IV, V, and VI c. I, II, and V d. IV, V, and VI e. another combination K a2 = 4.8 10 11 CH 3 NH 2 K b = 5.0 10 4 12. What is the concentration of H 3 O + ions in a solution in which ph = 4.32? a. 4.8 10 5 M b. 6.2 10 4 M c. 5.1 10 4 M d. 8.6 10 5 M e. 3.5 10 4 M

13. What is the ph of 400. ml of solution containing 0.0112 gram of HNO 3? a. 4.15 b. 3.35 c. 10.65 d. 3.75 e. 2.95 14. The ph of a 0.10 M solution of a monoprotic acid is 2.85. What is the value of the ionization constant of the acid? a. 6.3 10 5 b. 3.8 10 6 c. 2.0 10 5 d. 4.0 10 8 e. 7.2 10 6 15. Calculate the ph of 0.10 M HCN solution. K a = 4.0 10 10 a. 6.75 b. 5.20 c. 8.42 d. 9.52 e. 10.4 16. Assume that five weak acids, identified only by numbers (I, II, III, IV, and V), have the following ionization constants. Acid Ionization Constant (K a value) I. 1.0 10 3 II. 3.0 10 5 III. 2.6 10 7 IV. 4.0 10 9 V. 7.3 10 11 The anion of which acid is the weakest base? a. I b. II c. III d. IV e. V 17. What is the percent ionization for a 1.0 10 3 M solution of pyridine? K b = 1.5 10 9 a. 0.12% b. 1.6% c. 2.8% d. 0.045% e. 0.67% 18. Calculate the ph of a 0.050 M solution of hydroxylamine, NH 2 OH. K b = 6.6 10 9 a. 9.91 b. 9.48 c. 9.26

d. 10.56 e. 8.61 19. Which response list the species present in the highest concentration in a solution of 0.20 M H 3 PO 4? a. H 3 PO 4, H 2 PO 2 4, HPO 4 b. H 2 PO 4, HPO 2 3 4, PO 4 c. H 3 PO 4, H 3 O +, OH d. HPO 2 4, PO 3 4, OH e. H 3 PO 4, H 2 PO 4, H 3 O + 20. Which one of the following salts produces neutral solutions when it is dissolved in water? a. NaCN b. NaOCl c. NaF d. NaBr e. NaCH 3 COO 21. What is the value of the (base) hydrolysis constant for NaNO 2, sodium nitrite? K a = 4.5 10 4 for HNO 2. a. 4.5 10 4 b. 2.2 10 11 c. 4.5 10 18 d. 4.5 10 10 e. 2.1 10 9 22. Calculate the ph of 0.10 M solution of NaBO 2. a. 9.84 b. 12.89 c. 10.48 d. 11.11 e. 2.89 Chapter 19 Values The following equilibrium constants will be useful for the problems in this chapter. Substance Constant Substance Constant HCO 2 H K a = 1.8 10 4 H 2 CO 3 K 1 = 4.2 10 7 HNO 2 K a = 4.5 10 4 K 2 = 4.8 10 11 HOCl K a = 3.5 10 8 (COOH) 2 K 1 = 5.9 10 2 HF K a = 7.2 10 4 K 2 = 6.4 10 5 HCN K a = 4.0 10 10 CH 3 COOH K a = 1.8 10 5 H 2 SO 4 K 1 = very large HOCN K a = 3.5 10 4 K 2 = 1.2 10 2 C 6 H 5 NH 2 K b = 4.2 10 10 HOBr K a = 2.5 10 9 NH 3 K b = 1.8 10 5 23. A(n) solution contains a conjugate acid-base pair with both the acid and the base in reasonable concentrations. a. saturated b. electrolytic c. buffer

d. titrated e. equivalence 24. Calculate the ph of a solution that is 0.15 M in HOCl and 0.25 M in NaOCl. a. 7.23 b. 8.28 c. 8.06 d. 7.68 e. 9.10 25. What is the [H 3 O + ] of a solution that is 0.010 M in aqueous NH 3 and 0.030 M in NH 4 NO 3? a. 7.2 10 6 M b. 6.0 10 6 M c. 1.7 10 9 M d. 1.4 10 9 M e. 1.2 10 9 M 26. Which one of the following combinations cannot produce a buffer solution? a. HNO 2 and NaNO 2 b. HCN and NaCN c. HClO 4 and NaClO 4 d. NH 3 and (NH 4 ) 2 SO 4 e. NH 3 and NH 4 Br 27. What is the ph of a solution that is 0.15 M in HOCl and 0.25 M NaOCl after 0.050 mol HCl/L has been bubbled into the solution? a. 7.46 b. 6.15 c. 6.98 d. 7.23 e. 7.93 28. What ratio of NaOCN/HOCN will produce a buffer with ph = 3.10? a. 0.50 b. 1.1 c. 0.44 d. 2.3 e. 1.4 29. How many grams of KNO 2 must be added to 5.00 liters of 0.67 M HNO 2 solution to produce a buffer with ph = 3.15? Assume no change in volume. a. 181 g b. 3.15 g c. 270 g d. 53.6 g e. 315 g 30. Which titration curve could describe the titration of a solution of HCl by addition of a solution of KOH?

a. b. c. d. e. 31. Consider the titration of a weak acid with a strong base. Which of the following statements is incorrect? a. The solution is buffered before the equivalence point. b. The equivalence point would be greater than ph = 7.0. c. At the equivalence point, only water and a basic salt are present. d. KOH added to formic acid is an example of this. e. Methyl orange (ph color range 3.1 4.4) could be a suitable indicator. 32. Which acid / base pair would produce an acidic equivalence point? a. HCl / RbOH b. HCl / NH 3 c. CH 3 COOH / KOH d. H 2 SO 4 / Ca(OH) 2 e. HNO 3 / Ba(OH) 2

Chem1120pretest2Summeri2015 Answer Section MULTIPLE CHOICE 1. ANS: D PTS: 1 TOP: Chapter 17 Basic Concepts 2. ANS: E PTS: 1 TOP: The Equilibrium Constant 3. ANS: C PTS: 1 TOP: The Equilibrium Constant 4. ANS: A PTS: 1 TOP: The Equilibrium Constant 5. ANS: D PTS: 1 TOP: The Reaction Quotient 6. ANS: D PTS: 1 TOP: Uses of the Equilibrium Constant, Kc 7. ANS: C PTS: 1 TOP: Disturbing a System in Equilibrium: Predictions 8. ANS: B PTS: 1 TOP: Disturbing a System in Equilibrium: Predictions 9. ANS: B PTS: 1 TOP: Disturbing a System in Equilibrium: Predictions 10. ANS: A PTS: 1 TOP: The Brønsted-Lowry Theory 11. ANS: B PTS: 1 TOP: Review of Strong Electrolytes 12. ANS: A PTS: 1 TOP: The ph and poh Scales 13. ANS: B PTS: 1 TOP: The ph and poh Scales 14. ANS: C PTS: 1 15. ANS: B PTS: 1 16. ANS: A PTS: 1 17. ANS: A PTS: 1 18. ANS: C PTS: 1 19. ANS: E PTS: 1 TOP: Polyprotic Acids 20. ANS: D PTS: 1 TOP: Salts of Strong Bases and Strong Acids 21. ANS: B PTS: 1 TOP: Salts of Strong Bases and Weak Acids 22. ANS: D PTS: 1 TOP: Salts of Strong Bases and Weak Acids 23. ANS: C PTS: 1 TOP: The Common Ion Effect and Buffer Solutions 24. ANS: D PTS: 1 TOP: The Common Ion Effect and Buffer Solutions 25. ANS: C PTS: 1 TOP: The Common Ion Effect and Buffer Solutions 26. ANS: C PTS: 1 TOP: Buffering Action 27. ANS: A PTS: 1 TOP: Buffering Action 28. ANS: C PTS: 1 TOP: Preparation of Buffer Solutions 29. ANS: A PTS: 1 TOP: Preparation of Buffer Solutions 30. ANS: B PTS: 1 TOP: Strong Acid/Strong Base Titration Curves 31. ANS: E PTS: 1 TOP: Weak Acid/Strong Base and Weak Base/Strong Acid Titration Curves 32. ANS: B PTS: 1 TOP: Weak Acid/Strong Base and Weak Base/Strong Acid Titration Curves

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