19) The balanced half-reaction in which sulfate ion is reduced to sulfite ion is a __________ process.
A) four-electron
B) one-electron
C) two-electron
D) three-electron
E) six-electron
20) The electrode at which oxidation occurs is called the __________.
A) oxidizing agent
B) cathode
C) reducing agent
D) anode
E) voltaic cell
21) 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) MnO4– (aq) + 8H+ (aq) + 5e– → Mn2+ (aq) + 4H2O (l)
B) 2MnO4– (aq) + 12H+ (aq) + 6e– → 2Mn2+ (aq) + 3H2O (l)
C) Fe (s) → Fe3+ (aq) + 3e–
D) Fe (s) → Fe2+ (aq) + 2e–
E) Fe2+ (aq) → Fe3+ (aq) + e–
22) The half-reaction occurring at the cathode in the balanced reaction shown below is __________.
3MnO4– (aq) + 24H+ (aq) + 5Fe (s) → 3Mn2+ (aq) + 5Fe3+ (aq) + 12H2O (l)
A) MnO4– (aq) + 8H+ (aq) + 5e– → Mn2+ (aq) + 4H2O (l)
B) 2MnO4– (aq) + 12H+ (aq) + 6e– → 2Mn2+ (aq) + 3H2O (l)
C) Fe (s) → Fe3+ (aq) + 3e–
D) Fe (s) → Fe2+ (aq) + 2e–
E) Fe2+ (aq) → Fe3+ (aq) + e–
23) In a voltaic cell, electrons flow from the __________ to the __________.
A) salt bride, anode
B) anode, salt bridge
C) cathode, anode
D) salt bridge, cathode
E) anode, cathode
24) The reduction half reaction occurring in the standard hydrogen electrode is __________.
A) H2 (g, 1 atm) → 2H+ (aq, 1M) + 2e–
B) 2H+ (aq) + 2OH– → H2O (l)
C) O2 (g) + 4H+ (aq) + 4e– → 2H2O (l)
D) 2H+ (aq, 1M) + 2e– → H2 (g, 1 atm)
E) 2H+ (aq, 1M) + Cl2 (aq) → 2HCl (aq)
25) 1V = __________.
A) 1 amp ∙ s
B) 1 J/s
C) 96485 C
D) 1 J/C
E) 1 C/J
26) The more __________ the value of E°red, the greater the driving force for reduction.
A) positive
B) negative
C) exothermic
D) endothermic
E) extensive
Table 20.2
27) The standard cell potential (E°cell) for the voltaic cell based on the reaction below is __________ V.
Sn2+ (aq) + 2Fe3+ (aq) → 2Fe2+ (aq) + Sn4+ (aq)
A) +0.46
B) +0.617
C) +1.39
D) -0.46
E) +1.21
28) 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) -1.45
B) +2.99
C) +1.51
D) +3.05
E) +1.57
29) The standard cell potential (E°cell) for the voltaic cell based on the reaction below is __________ V.
2Cr (s) + 3Fe2+ (aq) → 3Fe (s) + 2Cr3+ (aq)
A) +0.30
B) +2.80
C) +3.10
D) +0.83
E) -0.16
18
30) The standard cell potential (E°cell) for the voltaic cell based on the reaction below is __________ V.
3Sn4+ (aq) + 2Cr (s) → 2Cr3+ (aq) + 3Sn2+ (aq)
A) +1.94
B) +0.89
C) +2.53
D) -0.59
E) -1.02
31) The relationship between the change in Gibbs free energy and the emf of an electrochemical cell is
given by __________.
A) ΔG =
–nF
E
B) ΔG =
-E
nF
C) ΔG = -nFE
D) ΔG = -nRTF
E) ΔG =
–nF
32) The standard cell potential (E°cell) of the reaction below is +0.126 V. The value of ΔG° for the
reaction is __________ kJ/mol.
Pb (s) + 2H+ (aq) → Pb2+ (aq) + H2 (g)
A) -24.3
B) +24.3
C) -12.6
D) +12.6
E) -50.8
19
33) The standard cell potential (E°cell) of the reaction below is –0.55 V. The value of ΔG° for the
reaction is __________ J/mol.
I2 (s) + 2Br– (aq) → 2I– (aq) + Br2 (l)
A) 0.54
B) 0.55
C) 5.5 × 10-6
D) 1.1 × 105
E) none of the above
34) The standard cell potential (E°cell) of the reaction below is –0.34 V. The value of ΔG° for the
reaction is __________ kJ/mol.
Cu (s) + 2H+ (aq) → Cu2+ (aq) + H2 (g)
A) -0.34
B) +66
C) -130
D) +130
E) none of the above
35) The standard cell potential (E°cell) of the reaction below is +1.34 V. The value of ΔG° for the
reaction is __________ kJ/mol.
3Cu (s) + 2MnO4– (aq) + 8H+ (aq) → 3Cu2+ (aq) + 2MnO2 (s) + 4H2O (l)
A) -24.3
B) +259
C) -259
D) +776
E) none of the above
36) The lead-containing reactant(s) consumed during recharging of a lead-acid battery is/are
__________.
A) Pb (s) only
B) PbO2 (s) only
C) PbSO4 (s) only
D) both PbO2 (s) and PbSO4 (s)
E) both Pb (s) and PbO2 (s)
37) Galvanized iron is iron coated with __________.
A) magnesium.
B) zinc.
C) chromium.
D) phosphate.
E) iron oxide.
38) Corrosion of iron is retarded by __________.
A) the presence of salts
B) high pH conditions
C) low pH conditions
D) both the presence of salts and high pH conditions
E) both the presence of salts and low pH conditions
20.3 Algorithmic Questions
1) 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 [Zn2+] = 1.0 M, the cell potential is 0.66 V. The concentration of H+ in the
cathode compartment is __________ M.
A) 2.0 × 10-2
B) 4.2 × 10-4
C) 1.4 × 10-1
D) 4.9 × 101
E) 1.0 × 10-12
21
2) A voltaic cell is constructed with two silver-silver chloride electrodes, where the half-reaction is
AgCl (s) + e– → Ag (s) + Cl– (aq) E° = +0.222 V
The concentrations of chloride ion in the two compartments are 0.0222 M and 2.22 M, respectively. The
cell emf is __________ V.
A) 0.212
B) 0.118
C) 0.00222
D) 22.2
E) 0.232
3) The standard cell potential (E°cell) for the reaction below is +0.63 V. The cell potential for this
reaction is __________ V when [Zn2+] = 3.5 M and [Pb2+] = 2.0 × 10-4 M.
Pb2+ (aq) + Zn (s) → Zn2+ (aq) + Pb (s)
A) 0.50
B) 0.84
C) 0.39
D) 0.76
E) 0.63
4) The standard cell potential (E°cell) for the reaction below is +1.10 V. The cell potential for this
reaction is __________ V when the concentration of [Cu2+] = 1.0 × 10-5 M and [Zn2+] = 3.5 M.
Zn (s) + Cu2+ (aq) → Cu (s) + Zn2+ (aq)
A) 1.42
B) 1.26
C) 0.94
D) 0.78
E) 1.10
22
5) A voltaic cell is constructed with two Zn2+-Zn electrodes, where the half-reaction is
Zn2+ + 2e– → Zn (s) E° = -0.763 V
The concentrations of zinc ion in the two compartments are 5.50 M and 1.11 × 10-2 M, respectively.
The cell emf is __________ V.
A) -1.54 × 10-3
B) -378
C) 0.0798
D) 0.160
E) -0.761
6) The standard emf for the cell using the overall cell reaction below is +2.20 V:
2Al (s) + 3I2 (s) → 2Al3+ (aq) + 6I– (aq)
The emf generated by the cell when [Al3+] = 4.5 × 10-3 M and [I–] = 0.15 M is ________ V.
A) 2.20
B) 2.32
C) 2.10
D) 2.39
E) 2.23
7) The standard emf for the cell using the overall cell reaction below is +0.48 V:
Zn (s) + Ni2+ (aq) → Zn2+ (aq) + Ni (s)
The emf generated by the cell when [Ni2+] = 2.50 M and [Zn2+] = 0.100 M is ________ V.
A) 0.40
B) 0.50
C) 0.52
D) 0.56
E) 0.44
8) How many kilowatt-hours of electricity are used to produce 3.00 kg of magnesium in the electrolysis
of molten MgCl2 with an applied emf of 4.50 V?
A) 0.0336
B) 0.0298
C) 7.4
D) 29.8
E) 14.9
9) The most useful ore of aluminum is bauxite, in which Al is present as hydrated oxides,
Al2O3 × H2O. The number of kilowatt-hours of electricity required to produce 4.00 kg of aluminum
from electrolysis of compounds from bauxite is __________ when the applied emf is 5.00 V.
A) 0.0168
B) 0.0596
C) 39.7
D) 19.9
E) 59.6
10) 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) 24.1
B) 0.0414
C) 0.0241
D) 48.3
E) 12.1
11) The electrolysis of molten AlCl3 for 3.25 hr with an electrical current of 15.0 A produces
__________ g of aluminum metal.
A) 147
B) 0.606
C) 4.55 × 10-3
D) 16.4
E) 49.1
12) How many seconds are required to produce 4.00 g of aluminum metal from the electrolysis of
molten AlCl3 with an electrical current of 12.0 A?
A) 27.0
B) 9.00
C) 1.19 × 103
D) 2.90 × 105
E) 3.57 × 103
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 39.5 amps in an electrolyte cell?
A) 5.14
B) 309
C) 103
D) 1.17
E) 15.4
14) What current (in A) is required to plate out 1.22 g of nickel from a solution of Ni2+ in 2.5 hour?
A) 65.4
B) 1.60 × 103
C) 0.446
D) 12.9
E) 0.891
15) How many grams of Ca metal are produced by the electrolysis of molten CaBr2 using a current of
30.0 amp for 9.0 hours?
A) 20.2
B) 404
C) 0.0622
D) 202
E) 101
25
16) How many grams of Cu are obtained by passing a current of 12 A through a solution of CuSO4 for
30 minutes?
A) 0.016
B) 7.1
C) 14
D) 28
E) 3.6
17) How many seconds are required to produce 1.0 g of silver metal by the electrolysis of a AgNO3
solution using a current of 5.0 amps?
A) 4.5 × 103
B) 3.2 × 103
C) 180
D) 3.7 × 10-5
E) 360
18) How many grams of copper will be plated out by a current of 2.3 A applied for 30 minutes to a 0.50
M solution of copper(II) sulfate?
A) 1.4
B) 2.7
C) 1.8 × 10-2
D) 3.6 × 10-2
E) 0.019
19) How many minutes will it take to plate out 4.56 g of Ni metal from a solution of Ni+2 using a
current of 55.5 amps in an electrolytic cell?
A) 2.25
B) 4.50
C) 4.55
D) 135
E) 270
20) How many minutes will it take to plate out 16.22 g of Al metal from a solution of Al+3 using a
current of 13.8 amps in an electrolytic cell?
A) 56.0
B) 70.0
C) 162
D) 210.
E) 12600
20.4 Short Answer
1) The most difficult species to reduce and the poorest oxidizing agent is __________.
2) At constant temperature and pressure the Gibbs free energy value is a measure of the __________ of
a process.
3) In the formula ΔG = -nFE, F is the __________.
4) The dependence of cell emf on concentration is expressed in the __________ equation.
5) The potential (E) to move K+ from the extracellular fluid to the intracellular fluid necessitates work.
The sign for this potential is __________.
6) The anode of the alkaline battery is powdered zinc in a gel that contacts __________.
7) The major product of a hydrogen fuel cell is __________.
8) When iron is coated with a thin layer of zinc to protect against corrosion, the iron is said to be
__________.
9) The quantity of charge passing a point in a circuit in one second when the current is one ampere is
called a __________.
10) Calculate the number of grams of aluminum produced in 30.0 minutes by electrolysis of AlCl3 at a
current of 12.0 A.
20.5 True/False Questions
1) The electrode where reduction occurs is called the anode.
2) In a voltaic cell electrons flow from the anode to the cathode.
3) When the cell potential is negative in a voltaic cell the cell reaction will not proceed spontaneously.
4) The standard reduction potential, E°red, is proportional to the stoichiometric coefficient.
5) The standard reduction potential of X is 1.23 V and that of Y is -0.44 V therefore X is oxidized by Y.
6) The lithium ion battery has more energy per unit mass than nickel-cadmium batteries.
7) Disadvantages of the methanol fuel cell compared to the hydrogen fuel cell are consumption of
catalyst and the production of a less environmentally safe product.
8) 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.
9) A positive number for maximum useful work in a spontaneous process (voltaic cell) indicates that the
cell will perform work on its surroundings.