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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
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 =
B) ΔG =
C) ΔG = -nFE
D) ΔG = -nRTF
E) ΔG =
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
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.
3 Cu (s) + 2 MnO4- (aq) + 8H+ (aq) → 3 Cu2+ (aq) + 2 MnO2 (s) + 4 H2O (l)
A) -24.3
B) +259
C) -259
D) +776
E) –776
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) What is the oxidation number of bromine in the HBrO molecule?
A) +1
B) +2
C) 0
D) -1
E) -2
2) What is the oxidation number of nitrogen in the NH2OH molecule?
A) -1
B) -2
C) -3
D) 0
E) +1
3) What is the oxidation number of sulfur in the S2O32– ion?
A) +2
B) +1
C) 0
D) -1
E) -2
4) Which substance is the oxidizing agent in the reaction below?
Fe(CO)5 (l) + 2HI (g) → Fe(CO)4I2 (s) + CO (g) + H2 (g)
A) HI
B) Fe(CO)5
C) Fe(CO)4I2
D) CO
E) H2
5) Which element is reduced in the reaction below?
Fe2+ + H+ + Cr2O72- → Fe3+ + Cr3+ + H2O
A) Cr
B) Fe
C) H
D) O
6) Which element is oxidized in the reaction below?
I- + MnO4- + H+ → I2 + MnO2 + cO
A) I
B) Mn
C) O
D) H
7) Which element is reduced in the following reaction?
Fe2S3 + 12HNO3 → 2Fe(NO3)3 + 3S + 6NO2 + 6H2O
A) N
B) S
C) H
D) O
E) NO2
8) What is the oxidation number of phosphorous in the PH3 molecule?
A) -3
B) -4
C) -5
D) +1
E) 0
9) What is the correct coefficient for the electrons in the following half-reaction:
Ni6+ + ___e– → Ni
A) 6
B) 1
C) 2
D) 3
E) 5
10) In the galvanic cell using the redox reaction below, the reduction half-reaction is ________.
Zn (s) + Cu2+ (aq) → Zn2+ (aq) + Cu (s)
A) Cu2+ + 2e– → Cu
B) Zn → Zn2+ + 2e–
C) Cu2+ → Cu + 2e–
D) Zn + 2e– → Zn2+
11) In the electrochemical cell using the redox reaction below, the cathode half-reaction is ________.
2H+ (s) + Sn (s) → Sn2+ (aq) + H2 (g)
A) 2H+ + 2e– → H2
B) Sn → Sn2+ + 2e–
C) 2H+ → H2 + 2e–
D) Sn + 2e– → Sn2+
E) Sn + 2e– → H2
12) In the electrochemical cell using the redox reaction below, the oxidation half reaction is ________.
Sn4+ (aq) + Fe (s) → Sn2+ (aq) + Fe2+ (aq)
A) Sn4+ + 2e– → Sn2+
B) Fe → Fe2+ + 2e–
C) Sn4+ → Sn2+ + 2e–
D) Fe + 2e– → Fe2+
E) Fe + 2e– → Sn2+
13) 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 0.53 V. The concentration of H+ in the cathode
compartment is ________ M.
A) 1.3 × 10-4
B) 1.7 × 10-8
C) 1.1 × 10-2
D) 7.7 × 103
E) 1.3 × 10-11
14) 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 0.0100 M and 1.55 M, respectively. The
cell emf is ________ V.
A) 0.216
B) 0.130
C) 0.00143
D) 34.4
E) 0.228
26
15) The standard cell potential (E° cell) for the reaction below is +0.63 V. The cell potential for this reaction
is ________ V when [ Zn2+] = 3.0 M and [Pb2+] = 2.0 × 10-4 M.
Pb2+ (aq) + Zn (s) → Zn2+ (aq) + Pb (s)
A) 0.51
B) 0.86
C) 0.40
D) 0.75
E) 0.63
16) 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+] = 3.0 M.
Zn (s) + Cu2+ (aq) → Cu (s) + Zn2+ (aq)
A) 1.42
B) 1.26
C) 0.94
D) 0.78
E) 1.10
17) 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 4.50 M and 1.11 × 10-2 M, respectively. The
cell emf is ________ V.
A) -1.88 × 10-3
B) -309
C) 0.0772
D) 0.154
E) -0.761
18) 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+] = 3.5 × 10-3 M and [I-] = 0.30 M is ________ V.
A) 2.20
B) 2.28
C) 2.12
D) 2.36
E) 2.23
19) 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+] = 0.100 M and [Zn2+] = 2.25 M is
A) 0.56
B) 0.50
C) 0.44
D) 0.40
E) 0.52
20) How many kilowatt-hours of electricity are used to produce 4.50 kg of magnesium in the electrolysis
of molten MgCl2 with an applied emf of 5.00 V?
A) 0.0201
B) 0.0496
C) 12.4
D) 49.6
E) 24.8
21) The most useful ore of aluminum is bauxite, in which Al is present as hydrated oxides, Al2O3 · xH2O.
The number of kilowatt-hours of electricity required to produce 3.00 kg of aluminum from electrolysis of
compounds from bauxite is ________ when the applied emf is 4.50 V.
A) 0.0249
B) 0.0402
C) 26.8
D) 13.4
E) 40.2
22) 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 4.50 kg of metallic sodium from the electrolysis of molten NaCl(s) is
________ when the applied emf is 5.00 V.
A) 26.2
B) 0.0381
C) 0.0262
D) 52.5
E) 13.1
23) The electrolysis of molten AlCl3 for 2.50 hr with an electrical current of 12.0 A produces ________ g of
aluminum metal.
A) 90.7
B) 0.373
C) 2.80 × 10-3
D) 10.1
E) 30.2
24) How many seconds are required to produce 5.00 g of aluminum metal from the electrolysis of molten
AlCl3 with an electrical current of 15.0 A?
A) 27.0
B) 9.00
C) 1.19E × 103
D) 2.90 × 105
E) 3.57 × 103
25) How many minutes will it take to plate out 2.19 g of chromium metal from a solution of Cr3+ using a
current of 19.5 amps in an electrolyte cell?
A) 10.4
B) 625
C) 208
D) 3.47
E) 31.2
26) What current (in A) is required to plate out 1.22 g of nickel from a solution of Ni2+ in 0.50 hour?
A) 65.4
B) 8.02 × 103
C) 2.22
D) 12.9
E) 4.46
27) How many grams of Ca metal are produced by the electrolysis of molten CaBr2 using a current of 30.0
amp for 8.0 hours?
A) 17.9
B) 359
C) 0.0622
D) 179
E) 89.7
30
28) How many grams of Cu are obtained by passing a current of 12 A through a solution of CuSO4 for
15 minutes?
A) 0.016
B) 3.6
C) 7.1
D) 14
E) 1.8
29) How many seconds are required to produce 1.0 g of silver metal by the electrolysis of a AgNO3
solution using a current of 60 amps?
A) 5.4 × 104
B) 3.2 × 103
C) 15
D) 3.7 × 10-5
E) 30
30) How many grams of copper will be plated out by a current of 2.3 A applied for 35 minutes to a 0.50 M
solution of copper (II) sulfate?
A) 1.6
B) 3.2
C) 1.8 × 10-2
D) 3.6 × 10-2
E) 0.019
31) How many minutes will it take to plate out 4.56 g of Ni metal from a solution of Ni2+ using a current
of 50.5 amps in an electrolytic cell?
A) 2.47
B) 4.95
C) 4.55
D) 148
E) 297
31
32) How many minutes will it take to plate out 16.22 g of Al metal from a solution of Al3+ using a current
of 14.6 amps in an electrolytic cell?
A) 53.0
B) 66.2
C) 153
D) 199
E) 11900
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) 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.
8) A positive number for maximum useful work in a spontaneous process (voltaic cell) indicates that the
cell will perform work on its surroundings.
