CHEMISTRY 102 EXAM 2 SECTIONS /10/2004

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1 2005 PECK Form C page1 CHEMISTRY 102 EXAM 2 SECTIONS /10/2004 NAME FORM C Directions: (1) Print your name. (2) Choose the best answer for the multiple choice questions (number 1-15). Transfer your multiple choice answers onto the scantron. Questions 1 15 are worth 6 points each (3) Answer the last two questions (numbers 16 & 17) directly on this exam. Those 2 questions are worth 5 points each and will be graded based upon what you write below each question. 1. Which of the statements concerning equilibrium is not true? (a) A system that is disturbed from an equilibrium condition responds in a manner to restore equilibrium. (b) Equilibrium in molecular systems is dynamic, with two opposing processes balancing one another. (c) The value of the equilibrium constant for a given reaction mixture is the same regardless of the direction from which equilibrium was attained. (d) A system moves spontaneously toward a state of equilibrium. (e) The equilibrium constant usually is independent of temperature. 2. Which one of the following substances is not a strong electrolyte? (a) NH 4 Cl (b) HClO 4 (c) HNO 3 (d) NH 3 (e) Mg(NO 3 ) 2 3. Consider the following reaction involving a solid. 2NH 4 NO 3 (s) 2NH 3 (g) + 2NO(g) + H 2 (g) + 2O 2 (g) The appropriate equilibrium constant expression would be: (a) K c = [NH 3 ][NO][H 2 ][O 2 ] (b) K c = [NH 3 ] 2 [NO] 2 [H 2 ][O 2 ] 2 (c) K c = [NH 3][NO][H 2 ][O 2 ] [NH 4 NO 3 ] (d) K c = [NH 3] 2 [NO] 2 [H 2 ][O 2 ] 2 [NH 4 NO 3 ] 2 (e) K c = [NH 3] 2 [NO] 2 [H 2 ][O 2 ] Under what condition is the H 3 O + concentration in water expected to be zero? (a) in a solution of a very strong acid (b) in a solution of a very strong base (c) in a solution of a very weak acid (d) in a solution of a very weak base (e) never

2 2005 PECK Form C page2 5. Which response includes all the true statements about a 0.10 M H 3 PO 4 solution and no false statements? I. The species present in highest concentration is nonionized H 3 PO 4. II. The species present in highest concentration is H 2 PO 2 4 ion. III. The species present in lowest concentration is H 2 PO 2 4 ion. IV. K 2 > K 3 (a) I and IV (b) II and IV (c) I and III (d) II and III (e) none of these 6. Trimethylamine ionizes as follows in water. What concentration of trimethylammonium ion, (CH 3 ) 3 NH +, is present in 9.0 x 10 2 M (CH 3 ) 3 N? K b = 7.4 x 10 5 (CH 3 ) 3 N + H 2 O (CH 3 ) 3 NH + + OH (a) 1.6 x 10 4 M (b) 5.2 x 10 3 M (c) 3.8 x 10 4 M (d) 2.6 x 10 3 M (e) 2.7 x 10 5 M 7. Calculate the ionization constant for a weak acid, HA, that is 2.3% ionized in M solution. (a) 4.2 x 10 5 (b) 3.9 x 10 5 (c) 2.2 x 10 2 (d) 4.7 x 10 3 (e) 8.2 x If mole of solid NaOH is added to 1.0 liter of M CH 3 COOH, what will the ph of the resulting solution be? Assume no volume change due to addition of NaOH. (a) 4.51 (b) 4.74 (c) 5.08 (d) 5.70 (e) Which salt is not derived from a strong acid and a strong soluble base? (a) BaCl 2 (b) Ca(NO 3 ) 2 (c) Li 2 SO 3 (d) CsBr (e) NaI 10. 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 x 10 3 II 3.0 x 10 5 III 2.6 x 10 7 IV 4.0 x 10 9 V 7.3 x A 0.10 M solution of which acid would have the highest ph (least acidic)? (a) I (b) II (c) III (d) IV (e) V

3 2005 PECK Form C page3 11. Which of the following salts will not yield an acidic solution when 0.01 M solutions are prepared? (a) NH 4 Cl (b) Al 2 (SO 4 ) 3 (c) FeSO 4 (d) Pb(NO 3 ) 2 (e) BeCl If the concentrations of the reactants and products in the following reaction are such that Q<K c in which direction will the reaction proceed in an attempt to establish equilibrium? A + 2B 2C + D (a) left to right (b) right to left (c) left to right only if the reaction is exothermic (d) left to right only if the reaction is endothermic (e) right to left only if the reaction is exothermic 13. For each of the following equilibria the value of K c is greater than 1. HClO + C 6 H 5 O ClO + C 6 H 5 OH HCOOH + ClO HCOO + HClO From these two equilibria, all the following conclusions can be drawn except:. (a) HCOOH is a stronger acid than HClO. (b) HClO is a stronger acid than C 6 H 5 OH. (c) C 6 H 5 O, ClO, and HCOO are Bronsted-Lowry bases (d) HClO is a strong acid. (e) ClO and HClO are a conjugate base and acid pair. 14. Which of the following equations can be used to solve for the thermodynamic (theoretical) equilibrium constant? (a) H f (reaction) = Σ n H f (products) - Σ n H f (reactants) (b) G = H - T S (c) G = G + RT ln Q (d) ln (K T2 /K T1 ) = H /R ((1/T 1 ) (1/T 2 )) (e) E = H - ( n)rt

4 2005 PECK Form C page4 15. The disproportion (auto-oxidation-reduction) of the XO ion to form XO 3 and X ions occurs in aqueous solution. If the rate expression for the reaction as written below is Rate =k [XO ], which of the following proposed mechanisms is consistent with this data? 3XO XO 3 + 2X (a) 2XO XO 2 + X XO + XO 2 XO 3 + X (slow) (b) XO X + O (slow) O + XO O 2 + X O 2 + X O 2 + X O 2 + XO XO 3 (c) XO O + X XO + O XO 2 (slow) XO + XO 2 XO 3 + X (d) XO O + X O + XO O 2 + X (slow) O 2 + XO XO 3 (e) 3XO XO 2 + X 2 O 2 (slow) X 2 O 2 XO + X XO + XO 2 XO 3 + X

5 2005 PECK Form C page5 NAME (print) (Signature) Seat # FORM C Separate this page from the rest of the exam. Answer questions 16 and 17 directly below each question. Draw a box around your answer. If you clearly show your set-up, you may receive partial credit even though your answer is wrong. Submit this page with the scantron as you leave the room. 16. (5pts) Calculate the ph of a solution prepared by mixing 50.0 ml of 0.10 M aqueous ammonia solution and 50.0 ml of water. 17. (5pts) Calculate the ph of a solution prepared by mixing 50.0 ml of 0.10 M aqueous ammonia solution and 50.0 ml of 0.10 M ammonium chloride solution. ANSWERS: 1 (E), 2 (D), 3 (B), 4 (E), 5 (A), 6 (D), 7 (A), 8 (B), 9 (C), 10 (E), 11 (D), 11 (D), 12 (A), 13 (D), 14 (C), 15 (B), 16 (10.98), 17 (9.26)