Chem1120pretest2Summeri2016

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1 Chem1120pretest2Summeri2016 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. Given the following reaction and its equilibrium constant at a certain temperature: N 2 (g) + 3H 2 (g) 2NH 3 (g) K c = Calculate the numerical value of the equilibrium constant for the following reaction at the same temperature. a b c d e NH 3 (g) N 2 (g) + H 2 (g) 3. 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 4. For a reversible reaction with a one-step mechanism, A B, the rate of the forward reaction is rate f = s 1 [A] and the rate of the reverse reaction is rate r = s 1 [B]. What is the value of K c for this reaction? a

2 b c d e Which of the following statements about the reaction quotient, Q, is false? a. The value of Q can be used to predict equilibrium concentrations. b. It has the same expression as K c. c. Its value is calculated using nonequilibrium concentrations. d. If Q > K c, the reaction must move to equilibrium by forming more reactants. e. If Q < K c, the reaction must move to equilibrium by forming more products. 6. 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), mol of HCl, and mol of O 2. Evaluate K c at that temperature. 2Cl 2 (g) + 2H 2 O(g) 4HCl(g) + O 2 (g) a b c d e 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. 8. The equilibrium constant, K c, is 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 M b M c M d M e M 9. 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.

3 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. 10. 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 For the gas phase reaction below, H 0 = 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. 12. Ammonium carbamate decomposes into NH 3 and CO 2 when heated. NH 4 (NH 2 CO 2 )(s) 2NH 3 (g) + CO 2 (g) If 25.0 g of ammonium carbamate is placed in an empty chamber and heated to 100 C, what are the equilibrium concentrations of NH 3 and CO 2? K c = 58.3 at 100 C. a. [NH 3 ] = 2.44 M; [CO 2 ] = 4.88 M b. [NH 3 ] = 4.88 M; [CO 2 ] = 2.44 M c. [NH 3 ] = 29.2 M; [CO 2 ] = 14.6 M d. [NH 3 ] = 15.3 M; [CO 2 ] = 7.64 M e. [NH 3 ] = 10.8 M; [CO 2 ] = 5.40 M 13. 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 14. For the following system, the equilibrium constant at 445 C is If a reaction is initiated with the following initial concentrations, [H 2 ] = M, [I 2 ] = M, and [HI] = 0, what will be the equilibrium concentration of HI? H 2 (g) + I 2 (g) 2HI(g) a M b M

4 c M d M e M 15. A reaction begins with mole of A and mole of B in a 2.00-L container at a certain temperature. What will be the equilibrium concentration of C? A(g) + B(g) C(g) K c = 23.5 a M b M c M d M e M Chapter 18 Values The following values will be useful for the problems in this chapter. Acid K Substance or Species K HF K a = NH 3 K b = HNO 2 K a = (CH 3 ) 3 N K b = CH 3 COOH K a = [Co(OH 2 ) 6 ] 2+ K a = HOCl K a = [Fe(OH 2 ) 6 ] 2+ K a = HOBr K a = [Fe(OH 2 ) 6 ] 3+ K a = HOCN K a = [Be(OH 2 ) 4 ] 2+ K a = HCN K a = [Cu(OH 2 ) 4 ] 2+ K a = H 2 SO 4 K a1 = very large HBO 2 K a = K a2 = (COOH) 2 K a1 = H 2 CO 3 K a1 = K a2 = 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 = CH 3 NH 2 K b = What is the concentration of H 3 O + ions in a solution in which ph = 4.32? a M b M c M

5 d M e M 18. What is the ph of 400. ml of solution containing gram of HNO 3? a b c d e The ph of a 0.10 M solution of a monoprotic acid is What is the value of the ionization constant of the acid? a b c d e Calculate the ph of 0.10 M HCN solution. K a = a b c d e 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 II III IV V The anion of which acid is the weakest base? a. I b. II c. III d. IV e. V 22. What is the percent ionization for a M solution of pyridine? K b = a. 0.12% b. 1.6% c. 2.8% d % e. 0.67% 23. Calculate the ph of a M solution of hydroxylamine, NH 2 OH. K b =

6 a b c d e 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 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 26. What is the value of the (base) hydrolysis constant for NaNO 2, sodium nitrite? K a = for HNO 2. a b c d e Calculate the ph of 0.10 M solution of NaBO 2. a b c d e Which of the following relationships in incorrect? Assume 25 C. a. ph + poh = b. [OH ] = 10 poh c. pk W = log K W d. [OH ] [H 3 O + ] = e. ph = log [H 3 O + ] 29. Calculate the concentrations of H 3 O + and OH ions in a 0.25 M HClO 4 solution. a. [H 3 O + ] = 0.25 M; [OH ] = 0.25 M b. [H 3 O + ] = 0.25 M; [OH ] = 4.0 M c. [H 3 O + ] = 0.25 M; [OH ] = M d. [H 3 O + ] = 0.50 M; [OH ] = M e. [H 3 O + ] = M; [OH ] = M 30. Calculate the ph of a solution in which [OH ] = M. a. 0.40

7 b c d e What is the poh of a solution in which [H 3 O + ] = M? a b c d e Which of the following statements about measurement of ph is incorrect? a. The ph of a solution can be determined using a ph meter. b. The ph of a solution can be determined by the indicator method. c. A ph meter is more accurate than an indicator for determining the ph. d. Many indicators are strong acids or strong bases. e. Acid-base indicators have different colors in solutions of different ph. 33. Consider calculations of [H 3 O+] in each of the following solutions. Do not go through the calculations. For which calculation is it not reasonable to assume that "x" is much less than the initial concentration? The x represents concentration ionized. a M H 2 O 2 K a = b M HCN K a = c M H 2 S K a1 = , K a2 = d M NH 3 K b = e M (COOH) 2 K a1 = , K a2 = Calculate the ionization constant for a weak acid, HA, that is 1.60% ionized in M solution. a b c d e The ph of a weak monoprotic acid (HA) is If the ionization constant for this acid is , what is the concentration of the weak acid? a M b M c M d M e M 36. The ph of a M solution of a weak acid, HA, is Calculate the percent ionization of the acid in M solution. a % b % c. 0.32% d. 0.68% e. 1.6%

8 37. The hypothetical weak acid H 2 A ionizes as shown below. Calculate the [HA ] in 0.20 M H 2 A. H 2 A H + + HA K a1 = HA H + + A 2 K a2 = a M b M c M d M e M 38. When salts derived from acids and bases are dissolved in water, the resulting solution is always acidic. a. strong; strong b. strong; weak c. weak; strong d. weak; weak e. no way to determine without K a and K b 39. When solid NH 4 NO 3 is added to water, the ph. a. remains at 7 b. becomes greater than 7 c. becomes less than 7 d. is independent of the amount dissolved e. Can not be determined 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 = H 2 CO 3 K 1 = HNO 2 K a = K 2 = HOCl K a = (COOH) 2 K 1 = HF K a = K 2 = HCN K a = CH 3 COOH K a = H 2 SO 4 K 1 = very large HOCN K a = K 2 = C 6 H 5 NH 2 K b = HOBr K a = NH 3 K b = 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

9 Chem1120pretest2Summeri2016 Answer Section MULTIPLE CHOICE 1. ANS: D PTS: 1 TOP: Chapter 17 Basic Concepts 2. ANS: D PTS: 1 TOP: Variation of Kc with the Form of the Balanced Equation 3. ANS: E PTS: 1 TOP: The Equilibrium Constant 4. ANS: C PTS: 1 TOP: The Equilibrium Constant 5. ANS: A PTS: 1 TOP: The Reaction Quotient 6. ANS: A PTS: 1 TOP: The Equilibrium Constant 7. ANS: D PTS: 1 TOP: The Reaction Quotient 8. ANS: D PTS: 1 TOP: Uses of the Equilibrium Constant, Kc 9. ANS: C PTS: 1 TOP: Disturbing a System in Equilibrium: Predictions 10. ANS: B PTS: 1 TOP: Disturbing a System in Equilibrium: Predictions 11. ANS: B PTS: 1 TOP: Disturbing a System in Equilibrium: Predictions 12. ANS: B PTS: 1 TOP: Uses of the Equilibrium Constant, Kc 13. ANS: A PTS: 1 TOP: The Brønsted-Lowry Theory 14. ANS: D PTS: 1 TOP: Uses of the Equilibrium Constant, Kc 15. ANS: D PTS: 1 DIF: Harder Question TOP: Uses of the Equilibrium Constant, Kc 16. ANS: B PTS: 1 TOP: Review of Strong Electrolytes 17. ANS: A PTS: 1 TOP: The ph and poh Scales 18. ANS: B PTS: 1 TOP: The ph and poh Scales 19. ANS: C PTS: ANS: B PTS: ANS: A PTS: ANS: A PTS: ANS: C PTS: ANS: E PTS: 1 TOP: Polyprotic Acids 25. ANS: D PTS: 1 TOP: Salts of Strong Bases and Strong Acids 26. ANS: B PTS: 1 TOP: Salts of Strong Bases and Weak Acids 27. ANS: D PTS: 1 TOP: Salts of Strong Bases and Weak Acids 28. ANS: B PTS: 1 TOP: The Autoionization of Water 29. ANS: C PTS: 1 TOP: The Autoionization of Water 30. ANS: D PTS: 1 TOP: The ph and poh Scales 31. ANS: D PTS: 1 TOP: The ph and poh Scales 32. ANS: D PTS: 1 TOP: The ph and poh Scales 33. ANS: E PTS: ANS: E PTS: 1

10 35. ANS: D PTS: ANS: C PTS: ANS: E PTS: 1 TOP: Polyprotic Acids 38. ANS: B PTS: 1 TOP: Salts of Strong Bases and Weak Acids 39. ANS: C PTS: 1 TOP: Salts of Strong Bases and Weak Acids 40. ANS: B PTS: 1 TOP: Weak Acid/Strong Base and Weak Base/Strong Acid Titration Curves