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Name:...... ........ Date:..... ......
South Carolina State University
300 COLLEGE STREET, NORTHEAST
O RANGEBURG, SOUTH CAROLINA 29117-
(803) 536-8513 and 536-
DEPARTMENT OF BIOLOGICAL AND PHYSICAL SCIENCEA FAX: (803) 536-4685 &536-
Multiple Choice: Identify the letter of the choice that best completes the statement or answers the question.
____ 1. In any electrochemical cell, the cathode is always __________. a. the positive electrode b. the negative electrode c. the electrode at which some species gains electrons d. the electrode at which some species loses electrons e. the electrode at which oxidation occurs
____ 2. The half-reaction that occurs at the cathode during the electrolysis of molten sodium bromide is __________. a. 2Br-^ → Br 2 + 2e- b. (^) Br 2 + 2e-^ → 2Br- c. Na+^ + e-^ → Na d. (^) Na → Na+^ + e- e. 2H 2 O + 2e-^ → 2OH-^ + H 2
____ 3. The electrolysis of molten lithium hydride using inert electrodes produces metallic lithium and gaseous hydrogen. What is the overall cell reaction? a. (^) LiH → Li + H 2 b. (^) LiH + H 2 O → Li + H 2 + OH- c. LiH + H+^ → Li + H 2 d. (^) LiOH + OH-^ → Li + H 2 + O 2 e. 2LiH → 2Li + H 2
____ 4. If 1 faraday of electricity is passed through an electrolytic cell containing a solution of a metal salt, the metal may be reduced and deposited at the cathode. Below are given the masses of metals that would be deposited from different salt solutions. Which one is incorrect? a. 107.9 g Ag from AgCl b. 31.8 g Cu from CuSO 4 c. 63.6 g Cu from CuCl d. 65.7 g Au from AuCl 3 e. 26.0 g Cr from Cr 2 (SO 4 ) 3
____ 5. How many coulombs of charge pass through a cell if 2.40 amperes of current are passed through the cell for 85. minutes? a. (^) 2.04 × 102 C b. (^) 1.33 × 10 -1^ C c. (^) 1.22 × 104 C d. 2.12 × 103 C e. 3.40 C
____ 6. How many faradays ( F ) are passed through a cell if 6.25 amperes of current are passed through the cell for 1. hours? a. 4.19 F b. 2.86 F c. 251 F d. 0.350 F e. 5.83 x 10-3^ F
____ 7. An aqueous copper(II) sulfate solution is electrolyzed for 45 minutes. A 3.2 ampere current is used. What mass of copper is produced? a. 0.95 g b. 1.9 g c. 2.8 g d. 4.6 g e. 5.5 g
____ 8. How long would a constant current of 4.5 amperes be required to flow in order to plate out 15 g of chromium from a chromium(III) sulfate solution? a. 268 hr b. 309 hr c. 5.15 hr d. 23.2 hr e. 1.72 hr
____ 9. How many mL of chlorine gas can be obtained at STP by the electrolysis of molten NaCl using a 0.500 ampere current for 25.0 minutes? a. 87.0 mL b. 48.7 mL c. 348 mL d. 174 mL e. 3.89 mL
____ 10. A cell is constructed by immersing a strip of lead in a 1.0 M Pb(NO 3 ) 2 solution and a strip of silver in a 1.0 M AgNO 3 solution. The circuit is completed by a wire and a salt bridge. As the cell operates, the strip of silver gains mass (only silver), and the concentration of silver ions in the solution around the silver strip decreases, while the strip of lead loses mass, and the concentration of lead ions increases in the solution around the lead strip. Which equation represents the reaction that occurs at the negative electrode in the above cell? a. Pb2+^ + 2e-^ → Pb b. Pb → Pb2+^ + 2e- c. Ag+^ + e-^ → Ag d. Ag → Ag+^ + e- e. none of the above
____ 11. Which of the following is the strongest oxidizing agent? a. Mg2+ b. Mg c. F 2 d. F- e. H+
____ 12. Which of the following describes the net reaction that occurs in the cell,
Cd|Cd2+(1 M )||Cu2+(1 M )|Cu? a. (^) Cu + Cd2+^ → Cu2+^ + Cd b. Cu + Cd → Cu2+^ + Cd2+ c. (^) Cu2+^ + Cd2+^ → Cu + Cd d. (^) Cu2+^ + Cd → Cu + Cd2+ e. (^) 2Cu + Cd2+^ → 2Cu+^ + Cd
____ 13. A voltaic cell is constructed by immersing a strip of copper metal in 1.0 M CuSO 4 solution and a strip of aluminum in 0.50 M Al 2 (SO 4 ) 3 solution. A wire and a salt bridge complete the circuit. The aluminum strip loses mass, and the concentration of aluminum ions in the solution increases. The copper electrode gains mass, and the concentration of copper ions decreases. What is the cell potential? a. +1.28 V b. +2.00 V c. +2.34 V d. +2.50 V e. +3.66 V
____ 20. A concentration cell is constructed by placing identical iron electrodes in two Fe2+^ solutions. The potential of this cell is observed to be 0.047 V. If the more concentrated Fe2+^ solution is 0.10 M , what is the concentration of the other Fe2+^ solution? a. (^) 1.5 × 10 -2^ M b. (^) 2.8 × 10 -5^ M c. (^) 3.5 × 10 -4^ M d. (^) 9.2 × 10 -2^ M e. (^) 2.6 × 10 -3^ M
____ 21. What is ∆ G^0 at 25°C for the reaction below? ( F = 96,500 J/V•mol e-)
Cu2+^ + Cd → Cu + Cd2+ a. -71.1 kJ b. -143 kJ c. 597 kJ d. 193 kJ e. +71.1 kJ
____ 22. The standard reduction potentials for the half-reactions Ag+(aq) + e-^ → Ag(s) and AgCl(s) + e-^ → Ag(s) + Cl-(aq) are 0.7994 and 0.222 volt, respectively. Calculate K sp for AgCl at 25°C. ( F = 96,500 J/V•mol e-^ and R = 8. J/mol•K) a. (^) 4.7 × 10 - b. (^) 3.2 × 10 - c. (^) 6.2 × 10 - d. (^) 4.3 × 10 - e. (^) 1.7 × 10 -
____ 23. Given the standard electrode potentials below, calculate K c at 25°C for the following reaction. ( F = 96, J/V•mol e-^ and R = 8.314 J/mol•K)
2Fe3+(aq) + 2I-(aq) → 2Fe2+(aq) + I 2 (s) E^0 Fe3+(aq) + e-^ → Fe2+(aq) +0.771 V I 2 (s) + 2e-^ → 2I-(aq) +0.535 V
a. (^) 1.6 × 1012 b. (^) 1.1 × 10 - c. (^) 1.0 × 10 - d. (^) 9.6 × 107 e. (^) 9.7 × 103
____ 24. The equilibrium constant, at 25°C, for the reaction below is 1.99 × 1020. What is E^0 for this reaction?
NO 3 -^ + 3H+^ + Cu → Cu2+^ + HNO 2 + H 2 O a. 0.090 V b. 0.60 V c. 0.88 V d. 1.05 V e. 0.21 V
