Chapter 18: Electrochemistry
1. Given the following reaction in acidic media:
Fe2+ + Cr2O72– → Fe3+ + Cr3+
answer the following question: The coefficient for water in the balanced reaction is:
A)
1
B)
3
C)
5
D)
7
E)
none of these
2. For the reaction of sodium bromide with chlorine gas to form sodium chloride and bromine,
the appropriate half-reactions are (ox = oxidation and re = reduction):
A)
ox: Cl2 + 2e– → 2Cl–; re: 2Br– → Br2 + 2e–
B)
ox: 2Br– → Br2 + 2e–; re: Cl2 + 2e– → 2Cl–
C)
ox: Cl + e– → Cl–; re: Br → Br– + e–
D)
ox: Br + 2e– → Br2–; re: 2Cl– → Cl2 + 2e–
E)
ox: 2Na+ + 2e– → 2Na; re: 2Cl– → Cl2 + 2e–
3. How many electrons are transferred in the following reaction when it is balanced in acidic
solution? SO32–(aq) + MnO4–(aq) → SO42–(aq) + Mn2+(aq)
A)
6
B)
2
C)
10
D)
5
E)
3
4. Ammonium metavandate reacts with sulfur dioxide in acidic solution as follows (hydrogen
ions and H2O omitted):
xVO3– + ySO2 → xVO2+ + ySO42–
The ratio x : y is
A)
1 : 1
B)
1 : 2
C)
2 : 1
D)
1 : 3
E)
3 : 1
The following reaction occurs in aqueous acid solution:
NO3– + I– → IO3– + NO2
5. In the balanced equation the coefficient of NO3– is:
A)
2
B)
3
C)
4
D)
5
E)
6
6. In the balanced equation the coefficient of water is:
A)
1
B)
2
C)
3
D)
4
E)
5
7. When the equation Cl2 → Cl– + ClO3– (basic solution) is balanced using the smallest whole-
number coefficients, the coefficient of OH– is:
A)
1
B)
12
C)
3
D)
4
E)
6
8. The following reaction occurs in basic solution:
F2 + H2O → O2 + F–
When the equation is balanced, the sum of the coefficients is:
A)
10
B)
11
C)
12
D)
13
E)
none of these
9. When the equation for the following reaction in basic solution is balanced, what is the sum
of the coefficients?
MnO2 + HO2– → MnO4–
A)
11
B)
31
C)
14
D)
9
E)
18
10. The reaction below occurs in basic solution. In the balanced equation, what is the sum of the
coefficients?
Zn + NO3– → Zn(OH)42– + NH3
A)
12
B)
15
C)
19
D)
23
E)
27
11. The following reaction occurs in basic solution: Ag+ + Cu → Ag + Cu2+ When the equation
is balanced, the sum of the coefficients is:
A)
4
B)
5
C)
6
D)
7
E)
none of the above
12. When the following reaction is balanced in acidic solution, what is the coefficient of I2?
IO3– + I– → I2
A)
1
B)
2
C)
3
D)
4
E)
none of these
13. Balance the following oxidation–reduction reaction using the half-reaction method.
Cr2O72– + I2 → Cr3+ + IO3–
In the balanced equation, the coefficient of water is:
A)
4
B)
17
C)
11
D)
7
E)
6
14. For the redox reaction 2Fe2+ + Cl2 → 2Fe3+ + 2Cl– which of the following are the correct
half-reactions?
I.
Cl2 + 2e– → 2Cl–
II.
Cl → Cl– + e–
III.
Cl2 → 2Cl– + 2e–
IV.
Fe2+ → Fe3+ + e–
V.
Fe2+ + e– → Fe3+
A)
I and IV
B)
I and V
C)
II and IV
D)
II and V
E)
III and IV
15. What is the oxidation state of Hg in Hg2Cl2?
A)
+2
B)
–1
C)
–2
D)
+1
E)
0
16. How many electrons are transferred in the following reaction?
2ClO3– + 12H+ + 10I– → 5I2 + Cl2 + 6H2O
A)
12
B)
5
C)
2
D)
30
E)
10
17. How many electrons are transferred in the following reaction?
A)
0
B)
1
C)
2
D)
4
E)
not enough information given
18. When the equation for the following reaction in basic solution is balanced, what is the sum
of the coefficients?
MnO4–(aq) + CN–(aq) → MnO2(s) + CNO–(aq)
A)
13
B)
8
C)
10
D)
20
E)
11
19. The following unbalanced equation represents a reaction that occurs in basic solution:
MnO42– + C2O42– → MnO2 + CO32–
How many moles of MnO42– are required to produce 1 mole of CO32–?
A)
4
B)
3
C)
2
D)
1
E)
none of these
20. The following questions refer to a galvanic cell that utilizes the following reaction
(unbalanced):
(AuCl4)–(aq) + Cu(s) → Au(s) + Cl–(aq) + Cu2+(aq)
Determine the number of electrons transferred during the reaction (when balanced).
A)
2
B)
3
C)
4
D)
6
E)
9
Consider a galvanic cell based in the reaction Fe2+ + Cr2O72– → Fe3+ + Cr3+ in acidic
solution.
21. What is the coefficient of Fe3+ in the balanced equation?
A)
6
B)
2
C)
3
D)
4
E)
none of these
22. Calculate the voltage of the standard cell carrying out this reaction.
A)
0
B)
0.21 V
C)
–0.21 V
D)
0.56 V
E)
–0.56 V
23. Which energy conversion shown below takes place in a galvanic cell?
A)
electrical to chemical
B)
chemical to electrical
C)
mechanical to chemical
D)
chemical to mechanical
E)
mechanical to electrical
24. Which of the following reactions is possible at the anode of a galvanic cell?
A)
Zn → Zn2+ + 2e–
B)
Zn2+ + 2e– → Zn
C)
Zn2+ + Cu → Zn + Cu2+
D)
Zn + Cu2+ → Zn2+ + Cu
E)
two of these
25. Which of the following is true for the cell shown here? Zn(s) | Zn2+(aq) Cr3+(aq) | Cr(s)
A)
The electrons flow from the cathode to the anode.
B)
The electrons flow from the zinc to the chromium.
C)
The electrons flow from the chromium to the zinc.
D)
The chromium is oxidized.
E)
The zinc is reduced.
26. The anode in a voltaic cell and in an electrolytic cell is
A)
positive in both cells
B)
the site of oxidation and of reduction, respectively
C)
the site of reduction and of oxidation, respectively
D)
the site of oxidation in both cells
E)
the site of reduction in both cells
27. Which statement is always true of the cathode in an electrochemical cell?
A)
It is considered the “negative” electrode.
B)
It is considered the “positive” electrode.
C)
Reduction occurs here.
D)
Metal is plated out here.
E)
Negative ions flow toward the cathode.
28. A strip of copper is placed in a 1 M solution of copper nitrate and a strip of silver is placed
in a 1 M solution of silver nitrate. The two metal strips are connected to a voltmeter by wires
and a salt bridge connects the solutions. The following standard reduction potentials apply:
Ag+(aq) + e– → Ag(s)
= +0.80 V
Cu2+(aq) + 2e– → Cu(s)
= +0.34 V
Which of the following statements is false?
A)
Electrons flow in the external circuit from the copper electrode to the silver
electrode.
B)
The silver electrode increases in mass as the cell operates.
C)
There is a net general movement of silver ions through the salt bridge to the copper
half-cell.
D)
Negative ions pass through the salt bridge from the silver half-cell to the copper
half-cell.
E)
Some positive copper ions pass through the salt bridge from the copper half-cell to
the silver half-cell.
29. You are told that metal X is a better reducing agent than metal Y. This must mean that:
A)
X+ is a better oxidizing agent than Y+.
B)
X+ is a better reducing agent than Y+.
C)
Y is a better oxidizing agent than X.
D)
Y+ is a better reducing agent than X+.
E)
Y+ is a better oxidizing agent than X+.
30. Which of the following species cannot function as an oxidizing agent?
A)
S(s)
B)
NO3–(aq)
C)
Cr2O72–(aq)
D)
I–(aq)
E)
MnO4–(aq)
31. Which of the following is the strongest oxidizing agent?
MnO4– + 4H+ + 3e– → MnO2 + 2H2O
= 1.68 V
I2 + 2e– → 2I–
= 0.54 V
Zn2+ + 2e– → Zn
= –0.76 V
A)
MnO4–
B)
I2
C)
Zn2+
D)
Zn
E)
MnO2
32. Which metal, Al or Ni could reduce Zn2+ to Zn(s) if placed in a Zn2+(aq) solution?
Zn2+ + 2e– → Zn
= –0.76 V
Al3+ + 3e– → Al
= –1.66 V
Ni2+ + 2e– → Ni
= –0.23 V
A)
Al
B)
Ni
C)
Both Al and Ni would work.
D)
Neither Al nor Ni would work.
E)
Cannot be determined.
33. Which of the following is the best reducing agent?
Cl2 + 2e– → 2Cl–
= 1.36 V
Mg2+ + 2e– → Mg
= –2.37 V
2H+ + 2e– → H2
= 0.00 V
A)
Cl2
B)
H2
C)
Mg
D)
Mg2+
E)
Cl–
34. Consider the galvanic cell shown below (the contents of each half-cell are written beneath
each compartment):
0.50 M Br2 0.20 M Cr3+
0.10 M Br–
The standard reduction potentials are as follows:
Cr3+(aq) + 3e– → Cr(s)
= –0.727 V
Br2(aq) + 2e– → 2Br–(aq)
= +1.090 V
What is
for this cell?
A)
1.817 V
B)
0.363 V
C)
–0.363 V
D)
4.724 V
E)
1.316 V
35. Consider the galvanic cell shown below (the contents of each half-cell are written beneath
each compartment):
0.50 M Br2 0.20 M Cr3+
0.10 M Br–
The standard reduction potentials are as follows:
Cr3+(aq) + 3e– → Cr(s)
= -0.73 V
Br2(aq) + 2e– → 2Br–(aq)
= +1.09 V
Which of the following statements about this cell is false?
Pt Cr
Pt Cr
A)
This is a galvanic cell.
B)
Electrons flow from the Pt electrode to the Cr electrode.
C)
Reduction occurs at the Pt electrode.
D)
The cell is not at standard conditions.
E)
To complete the circuit, cations migrate into the left half-cell and anions migrate
into the right half-cell from the salt bridge.
36. Refer to the galvanic cell below (the contents of each half-cell are written beneath each
compartment):
0.10 M MnO4– 0.40 M Cr3+
0.20 M Mn2+ 0.30 M Cr2O72–
0.010 M H+ 0.010 M H+
The standard reduction potentials are as follows:
MnO4– + 8H+ + 5e– → Mn2+ + 4H2O,
= 1.506 V
Cr2O72– + 14H+ + 6e– → 2Cr3+ + 7H2O,
= 1.330 V
What is the value of
cell?
A)
–0.176
B)
2.836
C)
0.176
D)
0.676
E)
6.200
Refer to the galvanic cell below (the contents of each half-cell are written beneath each
compartment):
Pt Cr
0.10 M MnO4– 0.40 M Cr3+
0.20 M Mn2+ 0.30 M Cr2O72–
0.010 M H+ 0.010 M H+
The standard reduction potentials are as follows:
MnO4– + 8H+ + 5e– → Mn2+ + 4H2O,
° = 1.51 V
Cr2O72– + 14H+ + 6e– → 2Cr3+ + 7H2O,
° = 1.33 V
37. When current is allowed to flow, which species is oxidized?
A)
Cr2O72–
B)
Cr3+
C)
MnO4–
D)
Mn2+
E)
H+
38. When current is allowed to flow, which species is reduced?
A)
Cr2O72–
B)
Cr3+
C)
MnO4–
D)
Mn2+
E)
H+
39. What is the oxidation state of Cr in Cr2O72–?
A)
+7
B)
+6
C)
+12
D)
–1
E)
–2
Pt Cr
40. What is the value of Q, the reaction quotient, for this cell reaction?
A)
6.7 1040
B)
1.5 10–41
C)
1.5 10–4
D)
6.7 103
E)
none of these
41. In which direction do electrons flow in the external circuit?
A)
left to right
B)
right to left
C)
no current flows; the cell is at equilibrium
D)
cannot be determined.
E)
none of these
42. In the balanced cell reaction, what is the stoichiometric coefficient for H+?
A)
5
B)
6
C)
30
D)
22
E)
2
43. How many electrons are transferred in the balanced reaction (i.e., what will be the value of n
in the Nernst equation)?
A)
5
B)
6
C)
30
D)
22
E)
2
44. What is the cell potential at 25°C as read on the digital voltmeter?
A)
0.18 V
B)
2.58 V
C)
0.10 V
D)
0.59 V
E)
0.26 V
45. A cell is set up with copper and lead electrodes in contact with CuSO4(aq) and
Pb(NO3)2(aq), respectively, at 25°C. The standard reduction potentials are:
Pb2+ + 2e– → Pb
= –0.13 V
Cu2+ + 2e– → Cu
= +0.34 V
If the Pb2+ and Cu2+ are each 1.0 M, the potential of the cell, in volts, is:
A)
0.47 V
B)
0.92 V
C)
0.22 V
D)
0.58 V
E)
none of these
46. Consider an electrochemical cell with a zinc electrode immersed in 1.0 M Zn2+ and a silver
electrode immersed in 1.0 M Ag+.
Zn2+ + 2e– → Zn
= –0.755 V
Ag+ + e– → Ag
= 0.800 V
Calculate
for this cell.
A)
0.045 V
B)
–0.045 V
C)
1.555 V
D)
–1.555 V
E)
none of these
47. The galvanic cell described by Zn(s) | Zn2+(aq) | Cu2+(aq) | Cu(s) has a standard cell
potential of 1.101 volts. Given that Zn(s) → Zn2+(aq) + 2e– has an oxidation potential of
0.764 volts, determine the reduction potential for .
A)
1.865 V
B)
–1.865 V
C)
–0.337 V
D)
0.337 V
E)
none of these
48. The following question refers to a galvanic cell that utilizes the following reaction
(unbalanced):
(AuCl4)–(aq) + Cu(s) → Au(s) + Cl–(aq) + Cu2+(aq)
Given the following information, determine the standard cell potential:
Species
Standard Reduction Potential (V)
Au3+(aq)
1.4980
Cu2+(aq)
A)
1.1590 V
B)
1.8370 V
C)
3.8160 V
D)
0.8200 V
E)
4.1550 V
49. Choose the correct statement given the following information:
A)
Fe2+(aq) is more likely to be oxidized than Fe2+ complexed to CN–.
B)
Fe3+(aq) is more likely to be reduced than Fe3+ complexed to CN–.
C)
Both A and B are true.
D)
Complexation of Fe ions with CN– has no effect on their tendencies to become
oxidized or reduced.
E)
None of these is true.
50. The following question refers to the following system:
3Ag(s) + NO3–(aq) + 4H+(aq) → 3Ag+(aq) + NO(g) + 2H2O(l)
Anode reaction:
Ag → Ag+(aq) + e–
= –0.7990 V
Cathode reaction:
NO3–(aq) + 4H+(aq) + 3e– → NO(g) + 2H2O(l)
= 0.9644 V
Determine the standard cell potential.
A)
–1.7634 V
B)
0.1654 V
C)
2.0942 V
D)
3.5268 V
E)
0.5878 V
51. Which of the following would be the best oxidizing agent?
A)
Cl2
B)
Fe
C)
Na
D)
Na+
E)
F–
52. Copper will spontaneously reduce which of the following?
A)
Fe2+ and Ag+
B)
Fe2+
C)
Ag+
D)
Al3+
E)
Fe2+ and Al3+
53. Determine the standard potential,
, of a cell that employs the reaction:
Fe + Cu2+ → Cu + Fe2+.
Reaction
(volts)
–0.441
+0.340
A)
–0.101
B)
–0.781
C)
0.101
D)
0.781
E)
–0.202
54. Of Sn2+, Ag+, and/or Zn2+, which could be reduced by Cu?
A)
Sn2+
B)
Ag+
C)
Zn2+
D)
Two of them could be reduced by Cu.
E)
All of them could be reduced by Cu.
55. You wish to plate out zinc metal from a zinc nitrate solution. Which metal, Al or Ni, could
you place in the solution to accomplish this?
A)
Al
B)
Ni
C)
Both Al and Ni would work.
D)
Neither Al nor Ni would work.
E)
Cannot be determined.
56. Which of the following is the best reducing agent?
A)
Cl2
B)
H2
C)
Mg
D)
Mg2+
E)
Cl–
57. What is the cell reaction for the voltaic cell Cr(s) | Cr3+(aq) || Cl–(aq) | Cl2(g) | Pt?
A)
Cr(s) + 2Cl–(aq)Cl2(g) + Cr3+(aq)
B)
2Cr3+(aq) + 6Cl–(aq) 2Cr(s) + 3Cl2(g)
C)
Cr(s) + 3Cl2(g)Cr3+(s) + 2Cl–(aq)
D)
2Cr(s) + 3Cl2(g) 2Cr3+(aq) + 6Cl–(aq)
E)
none of these
58. What is the balanced chemical equation corresponding to the following cell diagram?
Na(s) | Na+(aq) || Cu2+(aq) | Cu(s)
A)
2Na(s) + 2Na+(aq) → Cu2+(aq) + Cu(s)
B)
Cu(s) + 2Na+(aq) → 2Na(s) + Cu2+(aq)
C)
2Na(s) + Cu(s) → 2Na+(aq) + Cu2+(aq)
D)
Cu2+(aq) + Cu(s) → 2Na(s) + 2Na+(aq)
E)
2Na(s) + Cu2+(aq) → 2Na+(aq) + Cu(s)
59. Which of the following cell diagrams represents a galvanic cell? (
red(Sn2+/Sn) = –0.138V,
red(H+/H2) = 0.00 V)
A)
Pt(s), H2(g) | H+(aq) || Sn2+(aq) | Sn(s)
B)
Sn(s) | Sn2+(aq) || H+(aq) | H2(g), Pt(s)
C)
Sn(s), H2(g) | H+(aq) || Sn2+(aq) | Pt(s)
D)
Pt(s) | Sn2+(aq) || H+(aq) | H2(g), Sn(s)
E)
Sn(s) | Pt(s) || H+(aq), Sn2+(aq) | H2(g)
60. The following has a potential of 0.92 V:
If the concentrations of the ions were 1.0 M and the pressure of H2 were 1.0 atm, then
for
the half-reaction would be
A)
–0.92 V
B)
–0.46 V
C)
0.46 V
D)
0.92 V
E)
none of these
61. Consider the following electrode potentials:
Mg2+ + 2e– → Mg
= –2.37 V
V2+ + 2e– → V
= –1.19 V
Cu2+ + e– → Cu+
= 0.16 V
Which one of the reactions below will proceed spontaneously from left to right?
A)
Mg2+ + V → V2+ + Mg
B)
Mg2+ + 2Cu+ → 2Cu2+ + Mg
C)
V2+ + 2Cu+ → V + 2Cu2+
D)
V + 2Cu2+ → V2+ + 2Cu+
E)
none of these
62. What is
cell for the following electrochemical equation? (
red(Li+/Li) = –3.04 V,
red(Cu2+/Cu) = 0.342 V)
2Li(s) + Cu2+(aq) → 2Li+(aq) + Cu(s)
A)
–5.738 V
B)
6.422 V
C)
3.382 V
D)
–3.382 V
E)
–6.422 V
63. Which of the following cell reactions would require the use of an inert electrode?
A)
Co(s) + 2Ag+(aq) → Co2+(aq) + 2Ag(s)
B)
3Sr(s) + 2Au3+(aq) → 3Sr2+ + 2Au(s)
C)
3Rb+(aq) + Al(s) → 3Rb(s) + Al3+(aq)
D)
Ba(s) + 2MnO2(s) + 2NH4+(aq) → Ba2+(aq) + Mn2O3(s) + 2NH3(aq) + H2O(l)
E)
Sr(s) + 2Ag+(aq) → 2Ag(s) + Sr2+(aq)
64. Given:
2H+(aq) + 2e– → H2(g); 0.00 V
K+(aq) + e– → K(s); –2.93 V
F2(g) + 2e– → 2F–(aq); 2.87 V
Al3+(aq) + 3e– → Al(s); –1.66 V
Pb2+(aq) + 2e– → Pb(s); –0.13 V
Under standard-state conditions, which is the strongest reducing agent?
A)
H+
B)
K
C)
F–
D)
Al3+
E)
Pb2+
65. Which of the following statements is true concerning the electrochemical cell depicted
below?
Mg | Mg2+(aq) || Cu2+(aq) | Cu
Mg2+(aq) + 2e– → Mg(s); –2.38 V
Cu2+(aq) + 2e– → Cu(s); 0.34 V
A)
The cell reaction is spontaneous with a standard cell potential of 2.72 V.
B)
The cell reaction is spontaneous with a standard cell potential of 2.04 V.
C)
The cell reaction is nonspontaneous with a standard cell potential of –2.72 V.
D)
The cell reaction is nonspontaneous with a standard cell potential of –2.04 V.
E)
The cell is at equilibrium.
66. Which of the following statements is true concerning the electrochemical cell depicted
below?
Ca | Ca2+(aq) || K+(aq) | K
Ca2+(aq) + 2e– → Ca(s);
= –2.87 V
K+(aq) + e– → K(s);
= –2.93 V
A)
The cell reaction is spontaneous with a standard cell potential of 0.06 V.
B)
The cell reaction is nonspontaneous with a standard cell potential of –5.80 V.
C)
The cell reaction is nonspontaneous with a standard cell potential of –0.06 V.
D)
The cell reaction is spontaneous with a standard cell potential of 5.80 V.
E)
The cell is at equilibrium.
67. The reduction potentials for Au3+ and Ni2+ are as follows:
Au3+ + 3e– → Au,
= +1.50 V
Ni2+ + 2e– → Ni,
= –0.229 V
Calculate G° (at 25°C) for the reaction:
2Au3+ + 2Ni → 3Ni2+ + 2Au
A)
kJ
B)
kJ
C)
kJ
D)
kJ
E)
kJ
68. Tables of standard reduction potentials are usually given at 25°C.
depends on
temperature. Which of the following equations describes the temperature dependence of
?
A)
1.00 103
−7.36 102
7.36 102
−1.67 102
−1.00 103