Chemistry 112 Name Exam III Form A Section November 13,

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1 Chemistry 112 Name Exam III Form A Section November 13, IMPORTANT: On the scantron (answer sheet), you MUST clearly fill your name, your student number, section number, and test form (white cover = test form A; yellow cover = test form B). Use a #2 pencil. CHEMISTRY 112 EXAM 3 NOVERMBER 13, 2012 FORM A 1. The enthalpy of fusion of the metal tungsten is 35.4 kj/mol and the entropy of fusion is 9.61 J/mol-K. What is the melting point of tungsten, in degrees Celsius? A C B C C. 271 C D C E C 2. Given that the value of K a for NH 4 + is 5.6 x at 298 K, what is the Gibbs free energy of the acid hydrolysis reaction when [NH 4 + ] = 0.4 M, [NH 3] =0.2 M and [H + ]= M at the same temperature? There are 25 questions on this exam. Check that you have done all of the problems and filled in the first 25 bubbles on the scantron. The maximum score on this exam is 25 points. Your score will be reported in percent (max 100%). Exam policy Hints Calculators with text-programmable memory are not allowed. Relevant data and formulas, including the periodic table, are attached at the end of this exam. Your grade will be based only on what is on the scantron form. The answer key will be posted on the web after the exam (on the Exam Schedule page). You must turn in your cover sheet with your scantron answer form. As you read the question, underline or circle key words to highlight them for yourself. Avoid errors from "mis-reading" the question. Pay attention to units and magnitudes (decimal places) of numbers obtained from calculations. There is no penalty for guessing. A kj/mol B kj/mol C kj/mol D kj/mol E kj/mol 3. Dr. Gordon has constructed a voltaic cell in his secret laboratory using a 5.0 g Ni electrode in a solution with an initial concentration of 0.01 M Ni(NO 3) 2, and another 5.0 g Ni electrode in a solution with an initial concentration of 1.5 M Ni(NO 3) 2. Which statement is FALSE? A. The standard cell potential E is 0 V. B. The cell potential E cell will initially be V. C. The dilute solution acts as the anode and the concentrated solution acts as the cathode. D. The concentration of Ni 2+ ions in the dilute solution will increase as time passes. E. Replacing the 5.0 g Ni electrode in the dilute solution with a 10.0 g Ni electrode will increase the initial cell potential.

2 4. NaCN is added to a solution of 0.9 M FeCl 3 to form the soluble metal complex Fe(CN) 6 3. If the final concentration of CN is 0.5 M at equilibrium, what is the equilibrium concentration of uncomplexed Fe 3+ ions? The K f of Fe(CN) 6 3 is 1.0 x A. 5.8 x B. 1.8 x C. 9.4 x D. 4.5 x E. 1.4 x An electrochemical cell consisting of the reaction shown below is measured to have a voltage of V at 298K. What is the standard reduction potential of Au 3+? 2 Zn (s) + 2 Au 3+ (aq) 2 Zn 2+ (aq) + 3 Au (s) A V B V C V D V E V 5. The overall reaction shown below takes place in a lead acid battery. What substance is acting as the oxidizing agent? 8. Which statement regarding the following voltaic cell is true? 2 PbO 2 (s) + Pb (s) + 2 SO 4 (aq) + 4 H + (aq) 2 PbSO 4 (s) + 2H 2O (l) A. PbO 2 (s) B. Pb (s) 2 C. SO 4 (aq) D. H + (aq) E. H 2O (l) Cu 1M Cu(NO 3 ) 2 NaNO 3 1M FeCl 2 Fe 6. Which of the following salts exhibits the solubility dependence upon ph that is shown in the graph? A. Ca 3(PO 4) 2 B. Zn(OH) 2 C. MnCO 3 A. The Fe electrode is the cathode. B. The E cell is V. C. The Cu electrode will gain in mass as time passes. D. Both Na + and NO 3 ions will move towards the FeCl 2 solution. E. The cell is nonspontaneous as it is drawn. D. KClO 3 E. LaF ph

3 9. A voltaic cell is constructed based on the following unbalanced reaction. When the cell contains 6.0 grams I 2, 10.0 grams solid Cr, 0.3 M Cr 3+, and 0.2 M I at 298K, what is the cell voltage? I 2 (s) + Cr (s) I (aq) + Cr 3+ (aq) A V B V C V D V E V 11. To become a more efficient werewolf hunter Edward decides to have his dagger coated with silver. If he needs a coating of 2.5 grams of silver on his dagger, how long must he run a current of 0.85 amps through his dagger while submerged in a solution of 1.0 M AgNO 3? A minutes B. 294 minutes C minutes D minutes E minutes 12. Which one of the following reactions is NOT a redox reaction (does not involve oxidation and/or reduction)? 10. The hydrogen-oxygen fuel cell demonstrated in class uses the oxidation and reduction half reactions shown below. What is the maximum amount of work that the fuel cell could produce at 298 K with standard state conditions? H 2 (g) + 2 OH (aq) 2 H 2O (l) + 2 e O 2 (g) + 2 H 2O (l) + 4 e 4 OH (aq) A kj/mol B kj/mol C. 475 kj/mol D kj/mol E. 166 kj/mol E ox = V E red = V A. 2 Au(CN) 2 (aq) + Zn (s) Zn(CN) 4 2 (aq) + 2 Au (s) B. 2 C (s) + O 2 (g) 2 CO (g) C. Cu (s) Cu 2+ (aq) + 2 e D. CH 3OH (l) + O 2 (g) CO 2 (g) + H 2O (l) E. AgI (s) + 2 CN (aq) Ag(CN) 2 (aq) + I (aq) 13. What is the equilibrium constant for the disproportionation of Cu(I) at 298 K, as shown in the reaction below? A B x 10 6 C D x 10 5 E. 3.0 x Cu + (aq) Cu 2+ (aq) + Cu (s)

4 14. Which of the following are true for a voltaic cell at equilibrium? A. i only B. ii only C. iii only D. i and iii only E. i, ii and iii i. E cell = 0 ii. ΔG = 0 iii. Q = K 15. Which of the following solutions will form a solid precipitate of Ag 2SO 4? The K sp of Ag 2SO 4 is 1.5 x What is the equilibrium constant for the reaction of cyanide with silver iodide, as shown below? K sp (AgI) = 8.3 x 10 17, K f (Ag(CN) 2 ) = 1 x A 6.9 x B. 1.2 x C. 8.3 x 10 4 D. 1.5 x 10 5 E. 4.0 x 10 1 AgI (s) + 2 CN (aq) Ag(CN) 2 (aq) + I (aq) 18. The following unbalanced reaction takes place in a methanol fuel cell. What is the coefficient in front of water when the reaction is balanced in a low ph solution with whole number coefficients? A. 5 x 10 5 moles Na 2SO 4 added to 100 ml of 0.05 M AgNO 3 solution B. 5 x 10 3 moles Na 2SO 4 added to 100 ml of 0.05 M AgNO 3 solution C. 5 x 10 7 moles Na 2SO 4 added to 100 ml of 0.05 M AgNO 3 solution D. 1 x 10 6 moles Na 2SO 4 added to 100 ml of 0.05 M AgNO 3 solution E. All of the above mixtures will form a precipitate of Ag 2SO If the molar solubility of MnS is 4.47 x M at 298K, what is the K sp of MnS? A. 0 B. 1 C. 2 D. 3 E. 4 CH 3OH (l) + O 2 (g) CO 2 (g) + H 2O (l) A. 2 x B. 3.6 x C. 1 x D. 1.5 x 10 5 E. 1.8 x 10 11

5 19. Electrolysis is used commercially in the Hall Process for production of pure aluminum metal at high temperatures from Al 3+. The half reactions are shown below; the anodes are made from graphite and the cathode is aluminum. Which statement about this process is FALSE? C(s) + 2 O 2 (l) CO 2 (g) + 4e 3e + Al 3+ (molten cryolite) Al (l) A. The anode is the positive electrode, and the cathode is the negative electrode. B. The aluminum reduction process is spontaneous. C. The cell potential is negative. D. Reduction occurs at the cathode. E. Positive ions migrate to the cathode. 20. Why are secondary batteries such as the lead-acid battery and the nickel-metalhydride battery rechargeable, while alkaline dry cell batteries and regular alkaline flashlight batteries are not rechargeable? A. The electrolyte in the non-rechargeable batteries is not concentrated enough. B. Both the reactants and the products in the rechargeable batteries are in the solid state. C. The voltage in the non-rechargeable batteries is too low. D. The hydroxide ions in alkaline batteries interfere with the recharging process. E. An expensive catalyst would be required to charge alkaline batteries. 22. Which of the following is the strongest reducing agent? A. Cu + (aq) B. Cu (s) C. Fe 2+ (aq) D. H 2 (g) E. Br 2 (l) 23. What will be the initial product at the cathode in the electrolysis of aqueous lead sulfate, PbSO 4? A. Pb (s) 2 B. SO 3 (aq) C. H 2O (l) D. O 2 (g) E. H 2 (g) 21. Which situation will help prevent the corrosion of iron? A. The presence of concentrated salt water B. The presence of acidic water C. Attachment to a plate of solid copper D. Use of a platinum catalyst E. Coating with zinc metal 24. Which of the following will be able to spontaneously reduce Cd 2+? A. Ni 2+ B. F 2 C. Zn D. Pb E. Br 2 Go on to the last page

6 25. What is the concentration of free Ni 2+ ions in a saturated Ni(OH) 2 solution if the ph is buffered to remain at 8.4? The K sp of Ni(OH) 2 is 6.0 x A x 10 5 M B x M C x M D x 10 7 M E x M END OF TEST