MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.

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1 Chemistry 1C-Dr. Larson Chapter 20 Review Questions MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) is reduced in the following reaction: Cr2O S2O H + 2Cr3+ + 3S4O H2O A) S4O6 2- B) Cr2O7 2- C) Cr3+ D) S2O3 2- E) H + 2) Which substance is serving as the reducing agent in the following reaction? 14H + + Cr2O Ni 3Ni2+ + 2Cr3+ + 7H2O A) Ni B) H2O C) Cr2O7 2- D) Ni2+ E) H + 3) electrons appear in the following half-reaction when it is balanced. S4O6 2-2S2O3 2- A) 2 B) 4 C) 3 D) 1 E) 6 4) The balanced half-reaction in which dichromate ion is reduced to chromium(iii) ion is a process. A) three-electron B) six-electron C) twelve-electron D) four-electron E) two-electron 5) The half-reaction occurring at the anode in the balanced reaction shown below is. 3MnO4 - (aq) + 24H + (aq) + 5Fe (s) 3Mn2+ (aq) + 5Fe3+ (aq) + 12H2O (l) A) 2MnO4 - (aq) + 12H + (aq) + 6e - 2Mn2+ (aq) + 3H2O (l) B) Fe2+ (aq) Fe3+ (aq) + e - C) MnO4 - (aq) + 8H + (aq) + 5e - Mn2+ (aq) + 4H2O (l) D) Fe (s) Fe3+ (aq) + 3e - E) Fe (s) Fe2+ (aq) + 2e - 1

2 6) In a voltaic cell, electrons flow from the to the. A) anode, salt bridge B) cathode, anode C) anode, cathode D) salt bridge, cathode E) salt bride, anode 7) 1V =. A) 1 amp s B) 1 J/C C) C D) 1 J/s E) 1 C/J 8) The more the value of E red, the greater the driving force for reduction. A) negative B) extensive C) endothermic D) exothermic E) positive Table 20.2 Half-reaction E (V) Cr3+ (aq) + 3e - Cr (s) Fe2+ (aq) + 2e - Fe (s) Fe3+ (aq) + e - Fe2+ (s) Sn4+ (aq) + 2e - Sn2+ (aq) ) The standard cell potential (E cell) for the voltaic cell based on the reaction below is V. Cr (s) + 3Fe3+ (aq) 3Fe2+ (aq) + Cr3+ (aq) A) B) C) D) E) ) The standard cell potential (E cell) of the reaction below is V. The value of ΔG for the reaction is kj/mol. Pb (s) + 2H + (aq) Pb2+ (aq) + H2 (g) A) -24 B) +24 C) -12 D) +12 E) ) Galvanized iron is iron coated with. A) phosphate. B) magnesium. C) iron oxide. D) zinc. E) chromium. 2

3 12) Corrosion of iron is retarded by. A) high ph conditions B) the presence of salts C) low ph conditions D) both the presence of salts and high ph conditions E) both the presence of salts and low ph conditions 13) How many minutes will it take to plate out 2.19 g of chromium metal from a solution of Cr3+ using a current of 35.2 amps in an electrolyte cell? A) 5.77 B) 17.3 C) 1.92 D) 346 E) ) How many grams of CuS are obtained by passing a current of 12 A through a solution of CuSO4 for 15 minutes? A) 3.6 B) 1.8 C) 14 D) 7.1 E) ) Which of the following reactions is a redox reaction? (a) K2CrO4 + BaCl2 BaCrO4 + 2KCl (b) Pb Br - PbBr (c) Cu + S CuS A) (a) only B) (b) only C) (c) only D) (b) and (c) E) (a) and (c) 16) Which transformation could take place at the anode of an electrochemical cell? A) F2 tof - B) Cr2O7 2- Cr2+ C) O2 to H2O D) HAsO2 to As E) None of the above could take place at the anode. 17) The purpose of the salt bridge in an electrochemical cell is to. A) maintain electrical neutrality in the half-cells via migration of ions. B) provide a means for electrons to travel from the cathode to the anode. C) provide oxygen to facilitate oxidation at the anode. D) provide a means for electrons to travel from the anode to the cathode. E) provide a source of ions to react at the anode and cathode. 3

4 18) Which transformation could take place at the cathode of an electrochemical cell? A) Br2 BrO3 - B) NO HNO2 C) HSO4 - H2SO3 D) MnO2 MnO4 - E) Mn2+ MnO4-19) Which one of the following types of elements is most likely to be a good oxidizing agent? A) halogens B) alkaline earth elements C) lanthanides D) transition elements E) alkali metals 20) Which one of the following is the best oxidizing agent? A) Na B) H2 C) O2 D) Ca E) Li Table 20.1 Half Reaction E (V) F2 (g) + 2e - 2F - (aq) Cl2 (g) + 2e - 2Cl - (aq) Br2 (l) + 2e - 2Br - (aq) O2 (g) + 4H + (aq) + 4e - 2H2O (l) Ag + + e - Ag (s) Fe3+ (aq) + e - Fe2+ (aq) I2 (s) + 2e - 2I - (aq) Cu2+ + 2e - Cu (s) H + + 2e - H2 (g) 0 Pb2+ + 2e - Pb (s) Ni2+ + 2e - Ni (s) Li + + e - Li (s) ) Using Table 20.1, which substance can oxidize I - (aq) to I2 (s)? A) Cu2+ (aq) B) Br - (aq) C) Ag (s) D) Br2 (l) E) Ni2+ (aq) 4

5 Table 20.2 Half-reaction E (V) Cr3+ (aq) + 3e - Cr (s) Fe2+ (aq) + 2e - Fe (s) Fe3+ (aq) + e - Fe2+ (s) Sn4+ (aq) + 2e - Sn2+ (aq) ) Which of the following reactions will occur spontaneously as written? A) 3Sn4+ (aq) + 2Cr (s) 2Cr3+ (aq) + 3Sn2+ (aq) B) 3Fe2+ (aq) Fe (s) + 2Fe3+ (aq) C) Sn4+ (aq) + Fe3+ (aq) Sn2+ (aq) + Fe2+ (aq) D) Sn4+ (aq) + Fe2+ (aq) Sn2+ (aq) + Fe (s) E) 3Fe (s) + 2Cr3+ (aq) 2Cr (s) + 3Fe2+ (aq) 23) Consider an electrochemical cell based on the reaction: 2H + (aq) + Sn (s) Sn2+ (aq) + H2 (g) Which of the following actions would change the measured cell potential? A) increasing the [Sn2+] in the anode compartment B) increasing the pressure of hydrogen gas in the cathode compartment C) lowering the ph in the cathode compartment D) increasing the ph in the cathode compartment E) Any of the above will change the measure cell potential. 24) Consider an electrochemical cell based on the reaction: 2H + (aq) + Sn (s) Sn2+ (aq) + H2 (g) Which of the following actions would not change the measured cell potential? A) lowering the ph in the cathode compartment B) increasing the pressure of hydrogen gas in the cathode compartment C) addition of more tin metal to the anode compartment D) increasing the tin (II) ion concentration in the anode compartment E) Any of the above will change the measured cell potential. 5

6 25) Cathodic protection of a metal pipe against corrosion usually entails A) attaching an active metal to make the pipe the anode in an electrochemical cell. B) coating the pipe with another metal whose standard reduction potential is less negative than that of the pipe. C) attaching a dry cell to reduce any metal ions which might be formed. D) coating the pipe with a fluoropolymer to act as a source of fluoride ion (since the latter is so hard to oxidize). E) attaching an active metal to make the pipe the cathode in an electrochemical cell. 26) One of the differences between a voltaic cell and an electrolytic cell is that in an electrolytic cell. A) electrons flow toward the anode B) a nonspontaneous reaction is forced to occur C) O2 gas is produced at the cathode D) oxidation occurs at the cathode E) an electric current is produced by a chemical reaction 27) The standard cell potential (E ) of a voltaic cell constructed using the cell reaction below is 0.76 V: Zn (s) + 2H + (aq) Zn2+ (aq) + H2 (g) With PH2 = 1.0 atm and [Zn 2+] = 1.0 M, the cell potential is 0.66 V. The concentration of H + in the cathode compartment is M. A) B) C) D) E) ) A voltaic cell is constructed with two silver-silver chloride electrodes, where the half-reaction is AgCl (s) + e - Ag (s) + Cl - (aq) E = V The concentrations of chloride ion in the two compartments are M and 2.22 M, respectively. The cell emf is V. A) B) C) 22.2 D) E) ) The standard emf for the cell using the overall cell reaction below is V: 2Al (s) + 3I2 (s) 2Al3+ (aq) + 6I - (aq) The emf generated by the cell when [Al3+] = M and [I - ] = 0.15 M is V. A) 2.39 B) 2.20 C) 2.23 D) 2.30 E)

7 30) The town of Natrium, West Virginia, derives its name from the sodium produced in the electrolysis of molten sodium chloride (NaCl) mined from ancient salt deposits. The number of kilowatt-hours of electricity required to produce 4.60 kg of metallic sodium from the electrolysis of molten NaCl(s) is when the applied emf is 4.50 V. A) B) 24.1 C) 12.1 D) E) ) The electrolysis of molten AlCl3 for 3.25 hr with an electrical current of 15.0 A produces g of aluminum metal. A) 16.4 B) 147 C) 49.1 D) E) SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question. 32) In the formula ΔG = -nfe, F is the. 33) The dependence of cell emf on concentration is expressed in the. 34) A voltaic cell can be constructed of the same species as long as the are different. 35) The potential (E) to move K + from the extracellular fluid to the intracellular fluid necessitates work. The sign for this potential is. 36) The major product of a hydrogen fuel cell is. 37) When iron is coated with a thin layer of zinc to protect against corrosion, the iron is said to be. 38) The quantity of charge passing a point in a circuit in one second when the current is one ampere is called a. TRUE/FALSE. Write T if the statement is true and F if the statement is false. 39) The standard reduction potential, E o red, is proportional to the stoichiometric coefficient. 40) In a half reaction the amount of a substance that is reduced or oxidized is directly proportional to the number of electrons generated in the cell. 41) The standard reduction potential of X is 1.23 V and that of Y is V therefore X is oxidized by Y. 42) A positive number for maximum useful work in a spontaneous process (voltaic cell) indicates that the cell will perform work on its surroundings. 7

8 Answer Key Testname: CHAPTER 20 QUIZ 1) B Page Ref: Sec ) A Page Ref: Sec ) A Page Ref: Sec ) B Page Ref: Sec ) D 6) C 7) B 8) E 9) B 10) A Page Ref: Sec ) D Page Ref: Sec ) A Page Ref: Sec ) A 14) A 15) C Page Ref: Sec ) E 17) A 18) C 19) A 20) C 21) D 22) A Page Ref: Sec ) E 8

9 Answer Key Testname: CHAPTER 20 QUIZ 24) C 25) E Page Ref: Sec ) B 27) A 28) B 29) D 30) B 31) A 32) Faraday constant or the charge on one mole of electrons Page Ref: Sec ) Nernst equation Page Ref: Sec ) concentrations Page Ref: Sec ) negative Page Ref: Sec ) water Page Ref: Sec ) galvanized Page Ref: Sec ) coulomb Page Ref: Sec ) FALSE Page Ref: Sec ) TRUE Page Ref: Sec ) FALSE Page Ref: Sec ) FALSE Page Ref: Sec