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Practice Exam 3

# Practice Exam 3 - CHM2046 Exam 3 April 7 2005 Bubble in A B...

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CHM2046 Exam 3 April 7, 2005 Bubble in A, B or C as the test form code at the top right of your answer sheet. Also, be sure to bubble in your Section Number on your answer sheet. pH = -log[H 3 O + ] ΔG˚ = -RT lnK pK a = -log[K a ] ΔG˚ = -nF E˚ cell ΔG = ΔG˚ + RT lnQ E cell = E˚ cell - (0.0592 / n) log Q F = 9.65 x 10 4 J/V mol e - (or C/mol e - ) R = 8.31 J/K mol VERSION A 1. Consider the two half-reactions below: Fe 3+ (aq) + e - → Fe 2+ (aq) E˚ = 0.77 V Ce 4+ (aq) + e - → Ce 3+ (aq) E˚ = 1.61 V The spontaneous reaction obtained from these half-reactions is: a. Fe 2+ (aq) + Ce 3+ (aq) → Fe 3+ (aq) + Ce 4+ (aq) b. Fe 3+ (aq) + Ce 3+ (aq) → Fe 2+ (aq) + Ce 4+ (aq) c. Fe 3+ (aq) + Ce 4+ (aq) → Fe 2+ (aq) + Ce 3+ (aq) d. cannot be determined without ΔG˚ e. Fe 2+ (aq) + Ce 4+ (aq) → Fe 3+ (aq) + Ce 3+ (aq) 2. What is E˚ cell for the voltaic cell with cell reaction Fe (s) + Cl 2 (g) → Fe 2+ (aq) + 2 Cl - (aq) 3. For the voltaic cell Ni (s) | Ni 2+ (aq) || H 2 O 2 (aq), H + (aq) | graphite the cell reaction is: a. Ni 2+ (aq) + H 2 O 2 (aq) + 2 H + → Ni (s) + 2 H 2 O (l) b. Ni (s) + H 2 O 2 (aq) → 2 H + (aq) + H 2 O (l) + Ni 2+ (aq) c. Ni (s) + 2 H + (aq) + H 2 O (l) → Ni 2+ (aq) + 2 H 2 O 2 (l) d. H 2 O 2 (aq) + 2 H + (aq) + Ni (s) → Ni 2+ (aq) + 2 H 2 O (l) e. Ni 2+ (aq) + 2 H + (aq) → Ni (s) + 2 H 2 O 2 (l) 4. What spontaneous reaction will occur in a voltaic cell constructed using the following two half-reactions? Cr 3+ (aq) + 3 e - → Cr (s) E˚ = -0.74 V Fe 2+ (aq) + 2 e - → Fe (s) E˚ = -0.44 V

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5. For the voltaic (galvanic) cell made up of the Fe (s)/Fe 2+ (aq, 1.0 M) and Zn (s) / Zn 2+ (aq, 1.0 M) half-cells, given that Fe 2+ (aq) + 2 e - → Fe (s) E˚ = -0.44 V Zn 2+ (aq) + 2e - → Zn (s) E˚ = -0.76 V Which of the following statements is true?
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