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Form a 1 NAME: General Chemistry 116 Exam 2 Summer 2005 Announcement: If you complete chemskill for a previous chemistry 116, you do not have to redo it. Each question is worth 5 points. 1. 35 ml of 0.061 molar Zn(NO 3 ) 2 and 20 ml of KOH solution of ph 9 are mixed. Answer two questions. Zn(NO 3 ) 2, KOH and KNO 3 are freely soluble. Ksp for Zn(OH) 2 is 4.0 x 10-17 a. Will Zn(OH) 2 precipitate? a. yes b. no b. What is Q? a. 8.55 x 10-19 b. 2.62 x 10-4 c. 1.83 d. 5.15 x 10-10 e. 5.83 x 10-7 J f. 1.85 x 10-20 g. 1.22 x 10-10 h. 2.19 x 10-6 2. This question has two parts. a. For which of these processes will the entropy change of the system be negative? a. Iodine crystals sublime b. liquid ethanol vaporizes c. Benzene freezes d. NaCl is dissolves in water b. consider the reaction A + B -------- C S sys = -100 J/mol K ; Which is true? S suur = 125 J/mol K a. The reaction is spontaneous b. The reaction is spontaneous in the opposite direction c. The reaction is at equilibrium
Form a 2 3. This question has two parts. a. Consider the following equilibrium, contained in a sealed flask. N 2 (g) + O 2 (g) = 2NO(g) If we add more O 2, will the equilibrium shift to the right or left? a. no change b. left c. right b. Consider the following equilibrium, contained in a sealed flask. Hg(s) = Hg(g) If we increase the pressure at constant temperature, will the equilibrium shift to the right or left? a. no change b. left c. right 4. Consider the following equilibrium at 25 degrees C: 2POCl 3 (g) = 2PCl 3 (g) + O 2 (g) H = 508 kj If we increase the temperature at constant pressure, which of the following will occur? a. The reaction will shift to the left; Kp will decrease b. The reaction will shift to the right; Kp will decrease c. The reaction will shift to the left; Kp will increase d. The reaction will shift to the right; Kp will increase
Form a 3 5. Consider the following reaction H 2 (g) + CO 2 (g) = H 2 O(g) + CO(g) (Note: all species are in gas phase) The K a is 4.2 at 1650 degrees C. We start with 0.35 molar H 2 and 0.35 molar CO 2. What is the equilibrium concentration of H 2? a. 1.8 x 10-5 M b. 1.8 x 10-3 M c. 6.2 M d. 4.0 x 10-1 M e. 6.0 x 10-10 M f. 0.11 M g. 9.4 x 10-6 M h. 0. 032 M i. 0.0078 j. 0.98 6. Consider this reaction at 721 K. H 2 (g) + I 2 (g) = 2HI(g) If we start with 1.00 M H 2 and 2.00 Molar I 2, what is the equilibrium concentration of HI? K a = 50.5 a. 3.80 M b. 1.57 x 10-2 M c. 7.83 x 10-1 M d. 3.50 x 10-4 M e. 1.04 x 10-2 M f. 8.67 x 10-6 M g. 1.870 M h. 7.12 x 10-2 M i. 0.604 M j. 2.72 M k. 4.11 M 7. Which of the following is an acid/conjugate base pair? (Which of the following an acid and its own conjugate base?) a. H 2 SO 4 / SO 4 2- c. NH 4 + / NH2 - b. H 3 O + / OH - d. CH 3 COONa / CH 3 COO - e. NaOH / OH - f. HPO 4 2- / PO 4 3-8. Predict whether the equilibrium constant for the following reaction is greater than or smaller than or equal to 1.0. Refer to the table of acid and base strengths at the back of the exam. HF(aq) + HCOO - (aq) = F - (aq) + HCOOH(aq) a. equal to 1.0 b. less than 1.0 c. greater than 1.0
Form a 4 9. A solution has [OH - ] concentration equal to 3.61 x 10-10. What is the ph? a. 6.49 b. 7.27 c. 9.03 d. 2.19 e. 8.26 f. 1.88 g. 4.56 h. 13.1 10. The ph of a 0.100 molar formic acid (HCOOH) solution is 2.38 at 25 degrees C. Calculate the Ka at this temperature. HCOOH(aq) = H + (aq) + HCOO - (aq) a. 7.95 x 10-2 b. 1.80 x 10-4 c. 8.96 x 10-5 d. 1.48 x 10-1 e. 7.33 x 10-4 f. 6.75 x 10-3 g. 3.16 x 10-6 h. 1.28 x 10-6 11. Which statement is true? a. If a solution has a poh of 12.0, there are more H + ions in this solution then there are in pure water. b. If the poh of a solution is 3, the solution is acidic. c. HF is a weak acid, therefore 0.010 molar solution of HF will have 0.010 moles of H + in solution. d. a ph 12.0 solution of NaOH has a higher concentration of H + than a ph 10.0 solution of NaOH e. If a solution has a ph of 12.0, there are less OH - ions in this solution then there are in pure water. 12. What is the concentration of C 2 O 4 2- in a 0.20 M solution of oxalic acid? C 2 H 2 O 4 = C 2 HO 4 - + H + K a1 = 6.5 x 10-2 C 2 HO 4 - = C 2 O 4 2- + H + K a2 = 6.1 x 10-5 a. 6.7 x 10-8 M b. 0.0031 M c. 6.1 x 10-5 M d. 9.0 x 10-6 M e. 8.5 x 10-2 M f. 5.6 x 10-4 M g. 7.3 x 10-7 M h. 1.0 x 10-6 M
Form a 5 13. Refer to the following equilbria and equilibrium constants and answer the following two questions: NH 4 + (aq) + H2 O = NH 3 (aq) + H 3 O + (aq) K a = 5.6 x 10-10 - HNO 2 (aq) + H 2 O = NO 2 (aq) + H3 O + (aq) K a = 4.5 x 10-4 a. Is an aqueous solution of NH 4 Cl (ammonium chloride) acidic, basic or neutral? a. acidic b. neutral c. basic b. Is an aqueous solution of NH 4 NO 2 (ammonium nitrite) acidic, basic or neutral? a. acidic b. neutral c. basic 14. Calculate the ph at the equivalence point when 40.0 mls of 0.100 M benzoic acid is titrated with 40 mls 0.100 M NaOH. HC 7 H 5 O 2 (aq) = H + (aq) + C 7 H 5 O 2 - (aq) Ka = 6.3 x 10-5 a. 9.17 b. 3.22 c. 4.97 d. 10.1 e. 8.45 f. 9.00 g. 7.96 h. 6.07 15. What is the ph of a buffer that is 0.15 molar in lactic acid (HC 3 H 5 O 3 ) and 0.085 M in sodium lactate (C 3 H 5 O 3 - )? HC 3 H 5 O 3 (aq) = C 3 H 5 O 3 - (aq) + H + (aq) Ka = 1.4 x 10-4 a. 3.60 b. 7.29 c. 2.11 d. 1.59 e. 2.80 f. 8. 03 g. 5.04 h. 6.04
Form a 6 16. Calculate the ph when 45 mls of 0.100 M NaOH is added to 50.0 mls of 0.100 M CH 3 COOH (acetic acid) solution. CH 3 COOH(aq) = CH 3 COO - (aq) + H + (aq) K a = 1.8 x 10-5 a. 4.12 b. 8.21 c. 2.97 d. 5.69 e. 9.15 f. 5.06 g. 4.87 h. 6.42 17. Calculate the solubility of Zn(OH) 2 in grams per liter. K sp = 4.5 x 10-17 Zn(OH) 2 = 99.39 g/mol a. 3.30 x 10-3 g/l b. 9.35 x 10-4 g/l c. 3.99 x 10-7 g/l d. 6.71 x 10-6 g/l e. 2.91 x 10-2 g/l f. 1.84 x 10-7 g/l g. 4.61 x 10-1 g/l h. 2.20 x 10-4 g/l 18. The solubility of silver chromate was found experimentally to be 0.0435 grams per liter. Calculate the value for K sp. Ag 2 CrO 4 = 331.8 g/mol Ag 2 CrO 4 = 2Ag + + CrO 4 2- a. 5.75 x 10-5 b. 7.09 x 10-3 c. 1.96 x 10-7 d. 1.48 x 10-12 e. 1.33 x 10-9 f. 9.01 x 10-12 g. 4.32 x 10-11 h. 9.28 x 10-9 19. Refer to the following reaction. Cu(s) H 2 O(g) ---------------- CuO(s) + H 2 (g) H o = 84.5 and S o = - 48.7 J/mol K Which statement is true? a. The reaction is spontaneous only at high temperature. b. The reaction is spontaneous only at low temperature. c. The reaction is not spontaneous at any temperature. Reaction is spontaneous in the reverse direction at all temperatures. d. The reaction is spontaneous at every temperature.
Form a 7 Refer to the following equation and data and answer questions 20 and 21. N 2 H 4 (l) + 2H 2 O 2 (l) ---------- N 2 (g) + 4H 2 O(g) H rxn = -642.2 kj S o N 2 H 4 (l) = 121.2 J/mol K S o H 2 O(g) = 188.7 J/mol K S o N 2 (g) = 191.5 J/mol K S o H 2 O 2 (l) = 109.6 J/mol K 20. What is S o for the reaction at 25 degrees C? a. -6.78 x 10-2 J/mol K b. 1300 J/mol K c. 382.0 J/mol K d. 4.88 x 10 3 J/mol K e. -14.88 J/mol K f. 83.90 J/mol K g. 605.9 J/mol K h. -1.678 x 10 2 J/mol K 21. What is G o for the reaction at 25 degrees C? a. -119.6 kj b. -822.8 kj c. 224.1 kj d. -16.92 kj e. -230.9 kj f. 11.57 kj g. 458.4 kj h. -4047 kj
Form a 8 22. Consider the equilibrium 2SO 2 (g ) + O 2 (g) = 2SO 3 (g) K p for this reaction is 0.345 at 500K. At this temperature, the pressure of SO 2 is 0.165 atm and that of O 2 is 0.755atm. What is the pressure of SO 3 in the equilibrium mixture? a. 0.0842 atm b. 7.13 x 10-2 atm c. 29.8 atm d. 3.30 atm e. 0.752 atm f. 6.49 x 10-2 atm g. 3.02 x 10-1 atm h. 0.244 atm 23. Calculate the ph of a 0.20 M solution of HCN. Ka for HCN is 4.9 x 10-10. HCN(aq) = H + (aq) + CN - (aq) a. 7.45 b. 2.92 c. 3.90 d. 1.06 e. 1.20 f. 1.60 g. 8.18 h. 5.00