Chemistry: The Central Science, 13e (Brown et al.)
Chapter 20 Electrochemistry
20.1 Multiple-Choice
1) Which element is reduced in the reaction below?
Fe(CO)5 (l) + 2HI (g) → Fe(CO)4I2 (s) + CO (g) + H2 (g)
A) Fe
B) C
C) O
D) H
E) I
2) Which element is reduced in the reaction below?
Fe2+ + H+ + Cr2O72- → Fe3+ + Cr3+ + H2O
A) Fe
B) Cr
C) O
D) H
3) Which element is reduced in the reaction below?
I– + MnO4– + H+ → I2 + MnO2 + H2O
A) I
B) Mn
C) O
D) H
4) Which of the following reactions is a redox reaction?
(a) K2CrO4 + BaCl2 → BaCrO4 + 2KCl
(b) Pb22+ + 2Br– → PbBr
(c) Cu + S → CuS
A) (a) only
B) (b) only
C) (c) only
D) (a) and (c)
E) (b) and (c)
5) Which one of the following reactions is a redox reaction?
A) NaOH + HCl → NaCl + H2O
B) Pb2+ + 2Cl– → PbCl2
C) AgNO3 + HCl → HNO3 + AgCl
D) None of the above is a redox reaction.
6) Which substance is the oxidizing agent in the following reaction?
Fe2S3 + 12HNO3 → 2Fe(NO3)3 + 3S + 6NO2 + 6H2O
A) HNO3
B) S
C) NO2
D) Fe2S3
E) H2O
3
7) What is the coefficient of the permanganate ion when the following equation is balanced?
MnO4– + Br– → Mn2+ + Br2 (acidic solution)
A) 1
B) 2
C) 3
D) 5
E) 4
8) What is the coefficient of the dichromate ion when the following equation is balanced?
Fe2+ + Cr2O72- → Fe3+ + Cr3+ (acidic solution)
A) 1
B) 2
C) 3
D) 5
E) 6
9) What is the coefficient of Fe3+ when the following equation is balanced?
CN– + Fe3+ → CNO– + Fe2+ (basic solution)
A) 1
B) 2
C) 3
D) 4
E) 5
10) Which transformation could take place at the anode of an electrochemical cell?
A) Cr2O72- → Cr2+
B) F2 to F–
C) O2 to H2O
D) HAsO2 to As
E) None of the above could take place at the anode.
11) 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 source of ions to react at the anode and cathode
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 means for electrons to travel from the cathode to the anode
12) Which transformation could take place at the anode of an electrochemical cell?
A) NO → NO3–
B) CO2 → C2O42-
C) VO2+ → VO2+
D) H2AsO4 → H3AsO3
E) O2 → H2O2
13) Which transformation could take place at the cathode of an electrochemical cell?
A) MnO2 → MnO4–
B) Br2 → BrO3–
C) NO → HNO2
D) HSO4– → H2SO3
E) Mn2+ → MnO4–
Table 20.1
Half Reaction E°(V)
F2 (g) + 2e– → 2F– (aq) +2.87
Cl2 (g) + 2e– → 2Cl– (aq) +1.359
Br2 (l) + 2e– → 2Br– (aq) +1.065
O2 (g) + 4H+ (aq) + 4e– → 2H2O (l) +1.23
Ag+ + e– → Ag (s) +0.799
Fe3+ (aq) + e– → Fe2+ (aq) +0.771
I2 (s) + 2e– → 2I– (aq) +0.536
Cu2+ + 2e– → Cu (s) +0.34
2H+ + 2e– → H2 (g) 0
Pb2+ + 2e– → Pb (s) -0.126
Ni2+ + 2e– → Ni (s) -0.28
Li+ + e– → Li (s) -3.05
14) Which of the halogens in Table 20.1 is the strongest oxidizing agent?
A) Cl2
B) Br2
C) F2
D) I2
E) All of the halogens have equal strength as oxidizing agents.
15) Which one of the following types of elements is most likely to be a good oxidizing agent?
A) alkali metals
B) lanthanides
C) alkaline earth elements
D) transition elements
E) halogens
16) Which one of the following is the best oxidizing agent?
A) H2
B) Na
C) O2
D) Li
E) Ca
17) Which of the following reactions will occur spontaneously as written?
A) Sn4+ (aq) + Fe3+ (aq) → Sn2+ (aq) + Fe2+ (aq)
B) 3Fe (s) + 2Cr3+ (aq) → 2Cr (s) + 3Fe2+ (aq)
C) Sn4+ (aq) + Fe2+ (aq) → Sn2+ (aq) + Fe (s)
D) 3Sn4+ (aq) + 2Cr (s) → 2Cr3+ (aq) + 3Sn2+ (aq)
E) 3Fe2+ (aq) → Fe (s) + 2Fe3+ (aq)
18) Which of the following reactions will occur spontaneously as written?
A) 3Fe2+ (aq) + Cr3+ (aq) → Cr (s) + 3Fe3+ (aq)
B) 2Cr3+ (aq) + 3Sn2+ (aq) → 3Sn4+ (aq) + 2Cr (s)
C) Sn4+ (aq) + Fe2+ (s) → Sn2+ (aq) + Fe (s)
D) Sn2+ (aq) + Fe2+ (s) → Sn4+ (aq) + Fe3+ (aq)
E) 2Cr (s) + 3Fe2+ (s) → 3Fe (s) + 2Cr3+ (aq)
19) 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 pH in the cathode compartment
B) lowering the pH in the cathode compartment
C) increasing the [Sn2+] in the anode compartment
D) increasing the pressure of hydrogen gas in the cathode compartment
E) Any of the above will change the measure cell potential.
20) 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) addition of more tin metal to the anode compartment
C) increasing the tin (II) ion concentration in the anode compartment
D) increasing the pressure of hydrogen gas in the cathode compartment
E) Any of the above will change the measured cell potential.
21) What is the anode in an alkaline battery?
A) MnO2
B) KOH
C) Zn powder
D) Mn2O3
E) Pt
22) What is the cathode in an alkaline battery?
A) MnO2
B) KOH
C) Zn powder
D) Mn2O3
E) Pt
23) What is the cathode in the hydrogen fuel cell?
A) O2
B) KOH
C) Li
D) H2
E) Pt
24) In a lead-acid battery, the electrodes are consumed. In this battery, ________.
A) the anode is Pb
B) the anode is PbSO4
C) the anode is PbO2
D) the cathode is PbSO4
E) the cathode is Pb
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 an active metal to make the pipe the cathode in an electrochemical cell
D) attaching a dry cell to reduce any metal ions which might be formed
E) coating the pipe with a fluoropolymer to act as a source of fluoride ion (since the latter is so hard to
oxidize)
26) One of the differences between a voltaic cell and an electrolytic cell is that in an electrolytic cell,
________.
A) an electric current is produced by a chemical reaction
B) electrons flow toward the anode
C) a nonspontaneous reaction is forced to occur
D) O2 gas is produced at the cathode
E) oxidation occurs at the cathode
20.2 Bimodal Questions
1) The gain of electrons by an element is called ________.
A) reduction
B) oxidation
C) disproportionation
D) fractionation
E) sublimation
2) ________ is reduced in the following reaction:
Cr2O72- + 6S2O32- + 14H+ → 2Cr3+ + 3S4O62 + 7H2O
A) Cr6+
B) S2+
C) H+
D) O2-
E) S4O62-
3) ________ is oxidized in the following reaction:
Cr2O72- + 6S2O32- + 14H+ → 2Cr3+ + 3S4O62- + 7H2O
A) Cr6+
B) S2+
C) H+
D) O2-
E) S4O62-
4) ________ is the oxidizing agent in the reaction below.
Cr2O72- + 6S2O32- + 14H+ → 2Cr3+ + 3S4O62- + 7H2O
A) Cr2O72-
B) S2O32-
C) H+
D) Cr3+
E) S4O62-
5) ________ is the reducing agent in the reaction below.
Cr2O72- + 6S2O32- + 14H+ → 2Cr3+ + 3S4O62- + 7H2O
A) Cr2O72-
B) S2O32-
C) H+
D) Cr3+
E) S4O62-
6) Which substance is serving as the reducing agent in the following reaction?
14H+ + Cr2O72- + 3Ni → 3Ni2+ + 2Cr3+ + 7H2O
A) Ni
B) H+
C) Cr2O72-
D) H2O
E) Ni2+
7) Which substance is serving as the oxidizing agent in the following reaction?
14H+ + Cr2O72- + 3Ni → 3Ni2+ + 2Cr3+ + 7H2O
A) Ni
B) H+
C) Cr2O72-
D) H2O
E) Ni2+
8) Which substance is the reducing agent in the reaction below?
Pb + PbO2 + 2H2SO4 → 2PbSO4 + 2H2O
A) Pb
B) H2SO4
C) PbO2
D) PbSO4
E) H2O
9) Which substance is the oxidizing agent in the reaction below?
Pb + PbO2 + 2H2SO4 → 2PbSO4 + 2H2O
A) Pb
B) H2SO4
C) PbO2
D) PbSO4
E) H2O
10) What is the oxidation number of chromium in Cr2O72- ion?
A) +3
B) +12
C) +7
D) +6
E) +14
11) What is the oxidation number of potassium in KMnO4?
A) 0
B) +1
C) +2
D) -1
E) +3
12) What is the oxidation number of manganese in the MnO41– ion?
A) +1
B) +2
C) +5
D) +4
E) +7
13) What is the oxidation number of manganese in MnO2?
A) +3
B) +2
C) +1
D) +4
E) +7
14) What is the oxidation number of oxygen in H2O2?
A) -1
B) -2
C) +1
D) +2
E) -1/2
15) ________ electrons appear in the following half-reaction when it is balanced.
S4O62- → 2S2O32-
A) 6
B) 2
C) 4
D) 1
E) 3
16) The balanced half-reaction in which chlorine gas is reduced to the aqueous chloride ion is a ________
process.
A) one-electron
B) two-electron
C) four-electron
D) three-electron
E) six-electron
17) The balanced half-reaction in which dichromate ion is reduced to chromium metal is a ________
process.
A) two-electron
B) six-electron
C) three-electron
D) four-electron
E) twelve-electron
18) The balanced half-reaction in which dichromate ion is reduced to chromium (III) ion is a ________
process.
A) four-electron
B) twelve-electron
C) three-electron
D) six-electron
E) two-electron
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) + 5 → 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