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Name ______________________________ ID#_______________________ Section # ________ CH 1020 EXAM 3 Spring 2014 - Form A Fill in your name, CUID number and section on this test booklet. Fill in and bubble in your name, CUID number and section on the scantron form. For question #60 mark A. Mark the best answer using a #2 pencil and make clean erasures to insure proper scoring. Questions are worth four points each except as noted. Good Luck! 1. Nitrosyl bromide decomposes according to the following equation: 2NOBr(g) 2NO(g) + Br2(g) A 0.64 mol sample of NOBr was placed in a 1.0 L flask containing no NO or Br2. Upon reaching equilibrium, the flask contained 0.46 mol of NOBr. How many moles of NO and Br2, respectively, are in the flask at equilibrium? A. 0.18 mol, 0.18 mol B. 0.46 mol, 0.23 mol C. 0.18 mol, 0.090 mol D. 0.18 mol, 0.36 mol E. 0.46 mol, 0.46 mol 2. What are the signs of ?H, ?S, ?G for the boiling of water at a temperature of 50 °C. ?H ?S ?G A. B. + + + C. + + D. + E. + + 3. Identify the acid/base conjugate pair from the reaction below: HCO3(aq) + C5H5NH+(aq) ? H2CO3(aq) + C5H5N(aq) A. HCO3 & C5H5NH+ B. HCO3 & C5H5N C. C5H5NH+ & H2CO3 D. C5H5NH+ & C5H5N E. H2CO3 & C5H5N 4. The following curve represents a titration of ______ with ______. A. HCl, NaOH B. HF, NH3 C. HCl, NH3 D. HF, NaOH 5. Given the following cell, Al(s) | Al3+(aq) || Cd2+(aq) | Cd(s) What is the balanced overall (net) cell reaction? Al(s) + Cd2+(aq) ? Al3+(aq) + Cd(s) Al3+(aq) + Cd(s) ? Al(s) + Cd2+(aq) 2Al(s) + 3Cd2+(aq) ? 2Al3+(aq) + 3Cd(s) 2Al3+(aq) + 3Cd(s) ? 2Al(s) + 3Cd2+(aq) 3Al3+(aq) + 2Cd(s) ? 3Al(s) + 2Cd2+(aq) 6. Which solution will have the lowest pH? A. 0.10 M HCN D. 0.10 M H2CO3 B. 0.10 M HNO3 E. 0.10 M NaOH C. 0.10 M NaCl 7. For the following reaction at equilibrium, which one of the changes below would cause the Br2 concentration to increase? 2NOBr(g) 2NO(g) + Br2(g) ?H = +30 kJ A. Increase the temperature. B. Add more NO. C. Remove some NOBr. D. Compress the gas mixture into a smaller volume. 8. A buffer solution is represented in the diagram below. Which is the best representation of the buffer after the addition of some HCl? 428772127000A. C. B. D. 9. What is the pH of a 0.145 M propionic acid solution, CH3CH2COOH(aq)? (Ka(propionic acid) = 1.3 105) A. 0.00137 D. 2.86 B. 11.1 E. 4.87 C. 3.87 10. At what temperature would you expect dinitrogen pentoxide to sublime? N2O5(s) N2O5(g) N2O5(s) N2O5(g) Hf (kJmol1) 43.1 13.3 S (JK1mol1) 178.2 355.7 A. 104 C B. 0.32 C C. 45 C D. 54 C 11. Which is the weaker acid in each of the following pairs of acids? I. H2Te or HI II. H3PO4 or H3AsO4 A. H2Te; H3PO4 B. H2Te; H3AsO4 C. HI; H3PO4 D. HI; H3AsO4 E. cannot be determined 12. At 25 °C, ?G° for the reaction below is 5.97 kJ/mol. What is the equilibrium constant? 2HOCl(g) ? H2O(g) + Cl2O(g) A. 0.0898 B. 0.742 C. 1.00 D. 11.1 E. 1.49 103 13. What is the cell potential, Ecell, for the following galvanic cell at 25 C? A. 1.63 V D. 1.63 V B. 1.37 V E. 1.37 V C. 1.56 V 14. In which of these gas-phase equilibria is the yield of products increased by increasing the total pressure on the reaction mixture? A. CO(g) + H2O(g) CO2(g) + H2(g) B. PCl5(g) PCl3(g) + Cl2(g) C. 2NO(g) + Cl2(g) 2NOCl(g) D. H2(g) + I2(g) 2HI(g) 15. Which of the statements regarding the sublimation of carbon dioxide is true? CO2(s) CO2(g) A. G is more positive than H. B. H is more positive than G. C. G is exactly equal to H. D. S is negative. 16. What is the Kw of pure water at 50.0 °C if the pH is 6.630? A. 1.0 1014 B. 2.34 107 C. 5.50 1014 D. 2.13 1014 E. There is not enough information to solve 17. Which of the following acids and their conjugate base would be best to form a buffer with a pH of 3.51? A. HC7H5O2 pKa = 4.19 B. HF pKa = 3.46 C. HClO pKa = 7.54 D. HCN pKa = 9.31 E. HClO2 pKa = 1.96 18. Which of the following reagents is capable of reducing I2(s) to I(aq)? A. Pb2+(aq) C. Cl2(g) B. Ag(s) D. Ni(s) 19. Consider a cell that employs the following overall reaction: 2Al(s) + 3I2(s) ? 2Al3+(aq) + 6I(aq) What is ?Gº for the cell? A. 636 kJ/mol B. 648 kJ/mol C. 216 kJ/mol D. 636 kJ/mol E. 1270 kJ/mol 20. Calculate the percent dissociation of a 0.075 M solution of propanoic acid, CH3CH2COOH (Ka = 1.3 105). A. 0.0173% B. 0.758% C. 1.32% D. 10.1% E. 57.7% 21. At a certain temperature the equilibrium constant, Kc, equals 0.11 for the following reaction: 2 ICl(g) I2(g) + Cl2(g) What is the equilibrium concentration of ICl if 0.25 mol of I2 and 0.25 mol of Cl2 are initially mixed in a 2.0 L flask? A. 0.093 M B. 0.075 M C. 0.19 M D. 0.15 M E. 0.054 M 22. The standard cell potential for the following reaction is +0.63 V. What is the cell potential for reaction at 25 C when [Zn2+] = 1.0 M and [Pb2+] = 2.0 x 104 M? Pb2+(aq) + Zn(s) ? Zn2+(aq) + Pb(s) A. 0.52 V B. 0.85 V C. 0.41 V D. 0.74 V E. 0.63 V 23. Consider the following gas phase reaction at 25 C for which G = 104.7 kJ: NO2(g) + N2O(g) 3NO(g) What may be said about G for this mixture if the initial concentrations are: [NO2(g)] = 0.150 M [N2O(g)] = 0.150 M [NO(g)] = 0.0100 M A. G is more positive than G. B. G is less positive than G. C. G = G and the reaction is nonspontaneous. D. G = 0 and the reaction has reached equilibrium. E. G < 0 and the reaction is spontaneous under these conditions. 24. Which of the following salts will form an acidic aqueous solution? A. KCN C. CH3NH3Br B. CaCl2 D. Na2SO4 25. A 0.0500 mol sample of KOH is added to a 1 L buffer solution which contains 0.700 mol hypochlorous acid (HOCl) and 0.245 mol sodium hypochlorite (NaOCl). What is the resulting pH of the solution? (Ka(HOCl) = 3.5 10?8) A. 6.871 B. 7.113 C. 7.800 D. 8.041 E. 7.042 26. Representations of three acids are shown below. Which statement is correct regarding the conjugate bases of these three acids? A. X is the strongest base while Y is the weakest base. B. X is the strongest base while Z is the weakest base. C. Y is the strongest base while Z is the weakest base. D. Y is the strongest base while X is the weakest base. E. Z is the strongest base while Y is the weakest base. 60. Mark Answer A. USEFUL INFORMATION 08128000 Ho = Hof (products) - Hof (reactants) Go = Gof (products) - Gof (reactants) So = So (products) - So (reactants) Go = Ho TSo G = Go + RT ln Q Go = RT ln K Go = nFE At 298 K: At 298 K: Ka · Kb = Kw = 1.00 1014 at 25 °C 1 V = 1 J/C 1 F = 96,500 C/mol e R = 8.314 J/K·mol = 0.08206 L·atm/ K·mol 011620500 Table 1. Standard Reduction Potentials at 25 C Reduction Half Reaction Eo Au+(aq) + e- ? Au(s) 1.69 V Au3+(aq) + 3e- ? Au(s) 1.50 V Au3+(aq) + 2e- ? Au+(aq) 1.40 V Cl2(g) + 2e- 2Cl(aq) 1.36 V Br2(l) + 2e- 2Br (aq) 1.07 V Ag+(aq) + e- ? Ag(s) 0.80 V I2(s) + 2e- 2I (aq) 0.54 V Cu+(aq) + e- Cu(s) 0.52 V Cu2+(aq) + 2e- Cu(s) 0.34 V Cu2+(aq) + 2e- Cu+(aq) 0.15 V 2H+(aq) + 2e- H2(g) 0.00 V Pb2+(aq) + 2e- Pb(s) 0.13 V Ni2+(aq) + 2e- Ni(s) 0.26 V Cd2+(aq) + 2e- Cd(s) 0.40 V Zn2+(aq) + 2e- Zn(s) 0.76 V Al3+(aq) + 3e- Al(s) 1.66 V