Electrochemistry

71. In the electroplating of nickel, 0.200 faraday of electrical charge is passed through a solution of NiSO4. What mass of nickel is deposited? (A) 2.94 g (B) 5.86 g (C) 11.7 g (D) 58.7 g (E) 294 g

B

71 ... Fe(OH)2 + ... O2 + ... H2O ... Fe(OH)3 If 1 mole of O2 oxidizes Fe(OH)2 according to the reaction represented above, how many moles of Fe(OH)3 can be formed? (A) 2 (B) 3 (C) 4 (D) 5 (E) 6

C

75. If a copper sample containing some zinc impurity is to be purified by electrolysis, the anode and the cathode must be which of the following? Anode Cathode A. Pure copper Pure zinc B. Pure zinc Pure copper C. Pure copper Impure copper sample D. Impure copper sample Pure copper E. Impure copper sample Pure zinc

D

29. Cu(s) + 2 Ag+ Cu2+ + 2 Ag(s) If the equilibrium constant for the reaction above is 3.7 x 1015, which of the following correctly describes the standard voltage, E°, and the standard free energy change, ∆G°, for this reaction? (A) E° is positive and ∆G° is negative. (B) E° is negative and ∆G° is positive. (C) E° and ∆G° are both positive. (D) E° and ∆G° are both negative. (E) E° and ∆G° are both zero

A

18. 2 H2O + 4 MnO4− + 3 ClO2− 4 MnO2 + 3 ClO4− + 4 OH− Which species acts as an oxidizing agent in the reaction represented above? (A) H2O (B) ClO4− (C) ClO2− (D) MnO2 (E) MnO4−

E

19. In which of the following species does sulfur have the same oxidation number as it does in H2SO4? (A) H2SO3 (B) S2O32− (C) S2− (D) S8 (E) SO2Cl2

E

20. .....Mg(s) + .....NO3− (aq) +.....H+(aq) ......Mg2+(aq) + ....NH4+(aq) + ....H2O(l) When the skeleton equation above is balanced and all coefficients reduced to their lowest whole-number terms, what is the coefficient for H+ ? (A) 4 (B) 6 (C) 8 (D) 9 (E) 10

E

46. If 0.060 faradays are passed through an electrolytic cell containing a solution of In3+ ions, the maximum number of moles of In that could be deposited at the cathode is... (A) 0.010 mole (B) 0.020 mole (C) 0.030 mole (D) 0.060 mole (E) 0.18 mole

B

65. Which of the following species CANNOT function as an oxidizing agent? (A) Cr2O72− (B) MnO4− (C) NO3− (D) S (E) I−

E

29. When an aqueous solution of NaOH is added to an aqueous solution of potassium dichromate, K2Cr2O7 the dichromate ion is converted to... (A) CrO42− (B) CrO2 (C) Cr3+ (D) Cr2O3(s) (E) Cr(OH)3(s)

A

61. When acidified K2Cr2O7 solution is added to Na2S solution, green Cr3+ ions and free S are formed. When acidified K2Cr2O7 solution is added to NaCl, no change occurs. Of the substances involved in these reactions, which is the best reducing agent? (A) K2Cr2O7 (B) Na2S (C) Cr3+ (D) S (E) NaCl

B

63. Which of the following expressions is correct for the maximum mass of copper, in grams, that cou1d be plated out by electrolyzing aqueous CuCl2 for 16 hours at a constant current of 3.0 amperes? (1 faraday = 96,500 coulombs) (A) [(16)(3,600)(3.0)(63.55)(2)] / (96,500) (B) [(16)(3,600)(3.0)(63.55)] / [(96,500)(2)] (C) [(16)(3,600)(3.0)(63.55)] / (96,500) (D) [(16)(60)(3.0)(96,500)(2)] / (63.55) (E) [(16)(60)(3.0)(96,500)] / [(63.55)(2)]

B

22. __ Cr2O72− + __ e− + __ H+ __ Cr3+ + __ H2O(l) When the equation for the half reaction above is balanced with the lowest whole-number coefficients, the coefficient for H2O is... (A) 2 (B) 4 (C) 6 (D) 7 (E) 14

D

M(s) + 3 Ag+(aq) 3 Ag(s) + M3+(aq) E = +2.46 V Ag+(aq) + e− Ag(s) E = +0.80 V 57. According to the information above, what is the standard reduction potential for the half-reaction M3+(aq) + 3 e− M(s)? (A) −1.66 V (B) −0.06 V (C) 0.06 V (D) 1.66 V (E) 3.26 V

A

Questions 34-35 refer to an electrolytic cell that involves the following half-reaction: AlF63− + 3 e− Al + 6F− 34. Which of the following occurs in the reaction? (A) AlF 63− is reduced at the cathode. (B) Al is oxidized at the anode. (C) Aluminum is converted from the −3 oxidation state to the 0 oxidation state. (D) F− acts as a reducing agent. (E) F− is reduced at the cathode.

A

14. Questions 14-17 The spontaneous reaction that occurs when the cell in the picture operates is as follows: 2Ag+ + Cd(s) 2 Ag(s) + Cd2+ (A) Voltage increases. (B) Voltage decreases but remains > zero. (C) Voltage becomes zero and remains at zero. (D) No change in voltage occurs. (E) Direction of voltage change cannot be predicted without additional information. 14. A 50-milliliter sample of a 2-molar Cd(NO3)2 solution is added to the left beaker.

B

14. Questions 14-17 The spontaneous reaction that occurs when the cell in the picture operates is as follows: 2Ag+ + Cd(s) 2 Ag(s) + Cd2+ (A) Voltage increases. (B) Voltage decreases but remains > zero. (C) Voltage becomes zero and remains at zero. (D) No change in voltage occurs. (E) Direction of voltage change cannot be predicted without additional information. 17. Current is allowed to flow for 5 minutes.

B

20. What mass of Au is produced when 0.0500 mol of Au2S3 is reduced completely with excess H2? (A) 9.85 g (B) 19.7 g (C) 24.5 g (D) 39.4 g (E) 48.9 g

B

75. A direct-current power supply of low voltage (less than 10 volts) has lost the markings that indicate which output terminal is positive and which is negative. A chemist suggests that the power supply terminals be connected to a pair of platinum electrodes that dip into 0.1-molar KI solution. Which of the following correctly identifies the polarities of the power supply terminals? (A) A gas will be evolved only at the positive electrode. (B) A gas will be evolved only at the negative electrode. (C) A brown color will appear in the solution near the negative electrode. (D) A metal will be deposited on the positive electrode. (E) None of the methods above will identify the polarities of the power supply terminals.

B

14. Questions 14-17 The spontaneous reaction that occurs when the cell in the picture operates is as follows: 2Ag+ + Cd(s) 2 Ag(s) + Cd2+ (A) Voltage increases. (B) Voltage decreases but remains > zero. (C) Voltage becomes zero and remains at zero. (D) No change in voltage occurs. (E) Direction of voltage change cannot be predicted without additional information. 16. The salt bridge is replaced by a platinum wire.

C

36. Zn(s) + Cu2+ Zn2+ + Cu(s) An electrolytic cell based on the reaction represented above was constructed from zinc and copper half-cells. The observed voltage was found to be 1.00 volt instead of the standard cell potential, E°, of 1.10 volts. Which of the following could correctly account for this observation? (A) The copper electrode was larger than the zinc electrode. (B) The Zn2+ electrolyte was Zn(NO3)2, while the Cu2+ electrolyte was CuSO4. (C) The Zn2+ solution was more concentrated than the Cu2+ solution. (D) The solutions in the half-cells had different volumes. (E) The salt bridge contained KCl as the electrolyte.

C

42. . . . Li3N(s) + . . . H2O(l) . . . Li+(aq) + . . . OH− (aq) + . . . NH3(g) When the equation above is balanced and all coefficients reduced to lowest whole number terms, the coefficient for OH−(aq) is... (A) 1 (B) 2 (C) 3 (D) 4 (E) 6

C

79. 5 Fe2+ + MnO4− + 8 H+ ⇄ 5 Fe3+ + Mn2+ + 4 H2O In a titration experiment based on the equation above, 25.0 milliliters of an acidified Fe2+ solution requires 14.0 milliliters of standard 0.050-molar MnO4− solution to reach the equivalence point. The concentration of Fe2+ in the original solution is... (A) 0.0010 M (B) 0.0056 M (C) 0.028 M (D) 0.090 M (E) 0.14 M

C

14. Questions 14-17 The spontaneous reaction that occurs when the cell in the picture operates is as follows: 2Ag+ + Cd(s) 2 Ag(s) + Cd2+ (A) Voltage increases. (B) Voltage decreases but remains > zero. (C) Voltage becomes zero and remains at zero. (D) No change in voltage occurs. (E) Direction of voltage change cannot be predicted without additional information. 15. The silver electrode is made larger.

D

20. . . . Ag+ + . . . AsH3(g) + . . . OH− . . . Ag(s) + . . . H3AsO3(aq) + . . . H2O When the equation above is balanced with lowest whole-number coefficients, the coefficient for OH− is... (A) 2 (B) 4 (C) 5 (D) 6 (E) 7

D

34. ...CrO2− + ...OH− ... CrO42− + ... H2O + ... e− When the equation for the half-reaction above is balanced, what is the ratio of the coefficients OH− / CrO2− ? (A) 1:1 (B) 2:1 (C) 3:1 (D) 4:1 (E) 5:1

D

60. The standard reduction potentials for two half reactions are given above. The Nernst equation for a galvanic cell at 25° C in which Fe(s) reduces Ni2+ is the following: E = E° −0.059/2 log [Fe2+] / [Ni2+] What is the equilibrium constant for the reaction below? Fe(s) + Ni2+ Fe2+ + Ni(s) (A) 1.9 x 10−23 (B) 7.6 x 10−8 (C) 3.6 x 10+3 (D) 1.3 x 10+7 (E) 5.2 x 10+22

D

61. When a solution of potassium dichromate is added to an acidified solution of iron (II) sulfate, the products of the reaction are... (A) FeCr2O7(s) and H2O (B) FeCrO4(s) and H2O (C) Fe3+, CrO42−, and H2O (D) Fe3+, Cr3+, and H2O (E) Fe2(SO4)3(s), Cr3+ and H2O

D

H2Se(g) + 4 O2F2(g) SeF6(g) + 2 HF(g) + 4 O2(g) 30. Which of the following is true regarding the reaction represented above? (A) The oxidation number of O does not change. (B) The oxidation number of H changes from −1 to +1. (C) The oxidation number of F changes from +1 to −1. (D) The oxidation number of Se changes from −2 to +6. (E) It is a disproportionation reaction for F.

D

20. 6 I− + 2 MnO4− + 4 H2O(l) 3 I2(s) + 2 MnO2(s) + OH− Which of the following statements regarding the reaction represented by the equation above is correct? (A) Iodide ion is oxidized by hydroxide ion. (B) MnO4− is oxidized by iodide ion. (C) The oxidation number of manganese changes from +7 to +2. (D) The oxidation number of manganese remains the same. (E) The oxidation number of iodine changes from −1 to 0.

E