Chemistry: A Molecular Approach, 3e (Tro)
Chapter 18 Electrochemistry
Multiple Choice Questions
1) What element is being reduced in the following redox reaction?
MnO4⁻(aq) + H2C2O4(aq) → Mn2+(aq) + CO2(g)
A) C
B) O
C) Mn
D) H
2) What element is being oxidized in the following redox reaction?
MnO4⁻(aq) + H2C2O4(aq) → Mn2+(aq) + CO2(g)
A) C
B) O
C) Mn
D) H
3) What element is being reduced in the following redox reaction?
H2O2(l) + ClO2(aq) → ClO2⁻(aq) + O2(g)
A) H
B) O
C) Cl
D) N
E) C
4) What element is being oxidized in the following redox reaction?
H2O2(l) + ClO2(aq) → ClO2⁻(aq) + O2(g)
A) H
B) O
C) Cl
D) N
E) C
5) What element is being oxidized in the following redox reaction?
Cr(OH)4⁻(aq) + ClO⁻(aq) → CrO42-(aq) + Cl⁻(aq)
A) Cr
B) O
C) H
D) Cl
6) What element is being reduced in the following redox reaction?
Cr(OH)4⁻(aq) + ClO⁻(aq) → CrO42-(aq) + Cl⁻(aq)
A) Cr
B) O
C) H
D) Cl
7) What element is being oxidized in the following redox reaction?
C3H8O2(aq) + KMnO4(aq) → C3H2O4K2(aq) + MnO2(aq)
A) C
B) H
C) O
D) K
E) Mn
8) What element is being reduced in the following redox reaction?
C3H8O2(aq) + KMnO4(aq) → C3H2O4K2(aq) + MnO2(aq)
A) C
B) H
C) O
D) K
E) Mn
9) What element is being oxidized in the following redox reaction?
C3H8O2(aq) + K2Cr2O7(aq) → C3H4O4(aq) + Cr+3(aq)
A) C
B) H
C) O
D) K
E) Cr
10) What element is being reduced in the following redox reaction?
C3H8O2(aq) + K2Cr2O7(aq) → C3H4O4(aq) + Cr+3(aq)
A) C
B) H
C) O
D) K
E) Cr
11) Balance the following redox reaction if it occurs in H2SO4. What are the coefficients in front of
C3H8O2 and H2SO4 in the balanced reaction?
C3H8O2(aq) + K2Cr2O7(aq) → C3H4O4(aq) + Cr2(SO4)3(aq)
A) C3H8O2 = 3, H2SO4 = 8
B) C3H8O2 = 2, H2SO4 = 8
C) C3H8O2 = 1, H2SO4 = 16
D) C3H8O2 = 3, H2SO4 = 16
E) C3H8O2 = 2, H2SO4 = 4
12) Balance the following redox reaction if it occurs in H2SO4. What are the coefficients in front of
H2O and Cr2(SO4)3 in the balanced reaction?
C3H8O2(aq) + K2Cr2O7(aq) → C3H4O4(aq) + Cr2(SO4)3(aq)
A) H2O = 1, Cr2(SO4)3 = 5
B) H2O = 5, Cr2(SO4)3 = 2
C) H2O = 11, Cr2(SO4)3 = 4
D) H2O = 22, Cr2(SO4)3 = 4
E) H2O = 8, Cr2(SO4)3 = 2
13) Balance the following redox reaction if it occurs in acidic solution. What are the coefficients in
front of H2C2O4 and H2O in the balanced reaction?
MnO4⁻(aq) + H2C2O4(aq) → Mn2+(aq) + CO2(g)
A) H2C2O4 = 5, H2O = 8
B) H2C2O4 = 1, H2O = 1
C) H2C2O4 = 5, H2O = 1
D) H2C2O4 = 1, H2O = 4
E) H2C2O4 = 3, H2O = 2
14) Balance the following reaction in KOH. What are the coefficients in front of C3H8O2 and KMnO4
in the balanced reaction?
C3H8O2(aq) + KMnO4(aq) → C3H2O4K2(aq) + MnO2(aq)
A) C3H8O2 = 3, KMnO4 = 8
B) C3H8O2 = 3, KMnO4 = 4
C) C3H8O2 = 8, KMnO4 = 3
D) C3H8O2 = 2, KMnO4 = 4
E) C3H8O2 = 3, KMnO4 = 2
15) Balance the following reaction in KOH. What are the coefficients in front of H2O and KOH in the
balanced reaction and list which side of the equation that H2O and KOH appear?
C3H8O2(aq) + KMnO4(aq) → C3H2O4K2(aq) + MnO2(aq)
A) H2O = 1, KOH = 4, right
B) H2O = 4, KOH = 1, left
C) H2O = 8, KOH = 2 right
D) H2O = 3, KOH = 2, right
E) H2O = 4, KOH = 2, left
16) Balance the following redox reaction if it occurs in acidic solution. What are the coefficients in
front of H⁺ and Fe3+ in the balanced reaction?
Fe2+(aq) + MnO4⁻(aq) → Fe3+(aq) + Mn2+(aq)
A) H⁺ = 2, Fe3+ = 3
B) H⁺ = 8, Fe3+ = 5
C) H⁺ = 3, Fe3+ = 2
D) H⁺ = 5, Fe3+ = 1
E) H⁺ = 8, Fe3+ = 1
17) Balance the following redox reaction if it occurs in basic solution. What are the coefficients in front
of Br2 and OH⁻ in the balanced reaction?
Br2(l) → BrO3⁻(aq) + Br⁻(aq)
A) Br2 = 1, OH⁻ = 2
B) Br2 = 2, OH⁻ = 5
C) Br2 = 3, OH⁻ = 3
D) Br2 = 3, OH⁻ = 6
E) Br2 = 1, OH⁻ = 6
18) Balance the following redox reaction if it occurs in basic solution. What are the coefficients in front
of ClO2 and H2O in the balanced reaction?
H2O2(l) + ClO2(aq) → ClO2⁻(aq) + O2(g)
A) ClO2 = 1, H2O = 1
B) ClO2 = 1, H2O = 2
C) ClO2 = 4, H2O = 3
D) ClO2 = 4, H2O = 2
E) ClO2 = 2, H2O = 2
19) Balance the following redox reaction if it occurs in basic solution. What are the coefficients in front
of Cr(OH)4⁻ and ClO⁻ in the balanced reaction?
Cr(OH)4⁻(aq) + ClO⁻(aq) → CrO42-(aq) + Cl⁻(aq)
A) Cr(OH)4⁻ = 2, ClO⁻ = 3
B) Cr(OH)4⁻ = 1, ClO⁻ = 1
C) Cr(OH)4⁻ = 1, ClO⁻ = 2
D) Cr(OH)4⁻ = 2, ClO⁻ = 6
E) Cr(OH)4⁻ = 6, ClO⁻ = 5
20) Identify the location of oxidation in an electrochemical cell.
A) the anode
B) the cathode
C) the electrode
D) the salt bridge
E) the socket
21) Identify the location of reduction in an electrochemical cell.
A) the anode
B) the cathode
C) the electrode
D) the salt bridge
E) the socket
22) Define a salt bridge.
A) A pathway, composed of salt water, that ions pass through.
B) A pathway in which no ions flow.
C) A pathway between the cathode and anode in which ions are reduced.
D) A pathway between the cathode and anode in which ions are oxidized.
E) A pathway by which counterions can flow between the half-cells without the solutions in the half-cell
totally mixing.
23) Determine the cell notation for the redox reaction given below.
3 Cl2(g) + 2 Fe(s) → 6 Cl⁻(aq) + 2 Fe3+(aq)
A) Cl2(g) ∣ Cl⁻(aq) ∣ Pt Fe(s) ∣ Fe3+(aq)
B) Cl⁻(aq) ∣ Cl2(g) ∣ Pt Fe3+(aq) ∣ Fe(s)
C) Fe3+(aq) ∣ Fe(s) Cl⁻(aq) ∣ Cl2(g) ∣ Pt
D) Fe(s) ∣ Cl2(g) Fe3+(aq) ∣ Cl⁻(aq) ∣ Pt
E) Fe(s) ∣ Fe3+(aq) Cl2(g) ∣ Cl⁻(aq) ∣ Pt
24) What statement is NOT true about standard electrode potentials?
A) E°cell is positive for spontaneous reactions.
B) Electrons will flow from more negative electrode to more positive electrode.
C) The electrode potential of the standard hydrogen electrode is exactly zero.
D) E°cell is the difference in voltage between the anode and the cathode.
E) The electrode in any half-cell with a greater tendency to undergo reduction is positively charged
relative to the standard hydrogen electrode and therefore has a positive E°.
25) Which of the following is the weakest oxidizing agent?
A) H2O2(aq)
B) Fe3+(aq)
C) ClO2(g)
D) F–(s)
E) Fe(s)
8
26) Use the standard half-cell potentials listed below to calculate the standard cell potential for the
following reaction occurring in an electrochemical cell at 25°C. (The equation is balanced.)
3 Cl2(g) + 2 Fe(s) → 6 Cl⁻(aq) + 2 Fe3+(aq)
Cl2(g) + 2 e⁻ → 2 Cl⁻(aq) E° = +1.36 V
Fe3+(aq) + 3 e⁻ → Fe(s) E° = -0.04 V
A) +4.16 V
B) -1.40 V
C) -1.32 V
D) +1.32 V
E) +1.40 V
27) Use the standard half-cell potentials listed below to calculate the standard cell potential for the
following reaction occurring in an electrochemical cell at 25°C. (The equation is balanced.)
Pb(s) + Br2(l) → Pb2+(aq) + 2 Br⁻(aq)
Pb2+(aq) + 2 e⁻ → Pb(s) E° = -0.13 V
Br2(l) + 2 e⁻ → 2 Br⁻(aq) E° = +1.07 V
A) +1.20 V
B) +0.94 V
C) -0.94 V
D) -1.20 V
E) -0.60 V
28) Use the standard half-cell potentials listed below to calculate the standard cell potential for the
following reaction occurring in an electrochemical cell at 25°C. (The equation is balanced.)
Sn(s) + 2 Ag⁺(aq) → Sn2+(aq) + 2 Ag(s)
Sn2+(aq) + 2 e⁻ → Sn(s) E° = -0.14 V
Ag⁺(aq) + e⁻ → Ag(s) E° = +0.80 V
A) +1.74 V
B) +0.94 V
C) +1.08 V
D) -1.08 V
E) -1.74 V
29) Use the standard half-cell potentials listed below to calculate the standard cell potential for the
following reaction occurring in an electrochemical cell at 25°C. (The equation is balanced.)
Mg(s) + Cu2+(aq) → Cu(s) + Mg2+(aq)
Mg2+(aq) + 2 e⁻ → Mg(s) E° = -2.38 V
Cu2+(aq) + 2 e⁻ → Cu(s) E° = +0.34 V
A) +2.04 V
B) -2.04 V
C) +2.72 V
D) -1.36 V
E) +1.36 V
30) Use the standard half-cell potentials listed below to calculate the standard cell potential for the
following reaction occurring in an electrochemical cell at 25°C. (The equation is balanced.)
2 K(s) + I2(s) → 2 K⁺(aq) + 2 I⁻(aq)
K+(aq) + e⁻ → K(s) E° = -2.93 V
I2(s) + 2 e⁻ → 2 I⁻(aq) E° = +0.54 V
A) +6.40 V
B) +1.85 V
C) -5.32 V
D) +3.47 V
E) +5.32 V
31) Identify the characteristics of a spontaneous reaction.
A) ΔG° < 0
B) ΔE°cell > 0
C) K > 1
D) all of the above
E) none of the above
32) How many electrons are transferred in the following reaction? (The reaction is unbalanced.)
I2(s) + Fe(s) → Fe3+(aq) + I⁻(aq)
A) 1
B) 2
C) 6
D) 3
E) 4
33) Which of the following reactions would have the smallest value of K at 298 K?
A) A + B → C; E°cell = +1.22 V
B) A + 2 B → C; E°cell = +0.98 V
C) A + B → 2 C; E°cell = -0.030 V
D) A + B → 3 C; E°cell = +0.15 V
E) More information is needed to determine.
34) Use the tabulated half-cell potentials to calculate ΔG° for the following balanced redox reaction.
Pb2+(aq) + Cu(s) → Pb(s) + Cu2+(aq)
A) -41 kJ
B) -0.47 kJ
C) +46 kJ
D) +91 kJ
E) -21 kJ
35) Use the tabulated half-cell potentials to calculate ΔG° for the following balanced redox reaction.
3 I2(s) + 2 Fe(s) → 2 Fe3+(aq) + 6 I⁻(aq)
A) -1.1 x 102 kJ
B) +4.9 x 101 kJ
C) -9.7 x 101 kJ
D) +2.3 x 102 kJ
E) -3.3 x 102 kJ
11
36) Use the tabulated half-cell potentials to calculate ΔG° for the following redox reaction.
2 Al(s) + 3 Mg2+(aq) → 2 Al3+(aq) + 3 Mg(s)
A) +4.1 x 102 kJ
B) +1.4 x 102 kJ
C) -2.3 x 102 kJ
D) -7.8 x 102 kJ
E) +6.8 x 102 kJ
37) Which of the following reactions would be the most spontaneous at 298 K?
A) A + 2 B → C; E°cell = +0.98 V
B) A + B → 2 C; E°cell = -0.030 V
C) A + B → 3 C; E°cell = +0.15 V
D) A + B → C; E°cell = +1.22 V
E) More information is needed to determine.
38) Use the tabulated half-cell potentials to calculate the equilibrium constant (K) for the following
balanced redox reaction at 25°C.
2 Al(s) + 3 Mg2+(aq) → 2 Al3+(aq) + 3 Mg(s)
A) 1.1 × 1072
B) 8.9 × 10-73
C) 1.1 x 10-72
D) 1.0 × 1024
E) 4.6 × 1031
39) Use the tabulated half-cell potentials to calculate the equilibrium constant (K) for the following
balanced redox reaction at 25°C.
3 I2(s) + 2 Fe(s) → 2 Fe3+(aq) + 6 I⁻(aq)
A) 3.5 × 10-59
B) 1.1 × 1017
C) 2.4 × 1058
D) 8.9 × 10-18
E) 1.7 × 1029
40) Use the tabulated half-cell potentials to calculate the equilibrium constant (K) for the following
balanced redox reaction at 25°C.
Pb2+(aq) + Cu(s) → Pb(s) + Cu2+(aq)
A) 7.9 × 10-8
B) 8.9 × 107
C) 7.9 × 1015
D) 1.3 × 10-16
E) 1.1 × 10-8
41) Calculate the cell potential for the following reaction that takes place in an electrochemical cell at
25°C.
Sn(s) ∣ Sn2+(aq, 1.8 M) ∣∣ Ag+(aq, 0.055 M) ∣ Ag(s)
A) -0.94 V
B) -0.85 V
C) +1.02 V
D) +0.98 V
E) +0.86 V
42) Calculate the cell potential for the following reaction that takes place in an electrochemical cell at
25°C.
Sn(s) ∣ Sn2+(aq, 0.022 M) ∣∣ Ag+(aq, 2.7 M) ∣ Ag(s)
A) +1.01 V
B) -0.83 V
C) +1.31 V
D) +0.01 V
E) -0.66 V
43) Calculate the cell potential for the following reaction that takes place in an electrochemical cell at
25°C.
Mg(s) ∣ Mg2+(aq, 2.74 M) ∣∣ Cu2+(aq, 0.0033 M) ∣ Cu(s)
A) -2.80 V
B) +2.62 V
C) +2.71 V
D) +2.12 V
E) -1.94 V
44) Calculate the cell potential for the following reaction that takes place in an electrochemical cell at
25°C.
Fe(s) ∣ Fe3+(aq, 0.0011 M) ∣∣ Fe3+(aq, 2.33 M) ∣ Fe(s)
A) +0.066 V
B) -0.036 V
C) 0.00 V
D) -0.099 V
E) +0.20 V
45) Calculate the cell potential for the following reaction that takes place in an electrochemical cell at
25°C.
Cu(s) ∣ Cu2+(aq, 0.0032 M) ∣∣ Cu2+(aq, 4.48 M) ∣ Cu(s)
A) 0.00 V
B) +0.093 V
C) +0.34 V
D) +0.186 V
E) +0.052 V
46) Calculate the cell potential for the following reaction that takes place in an electrochemical cell at
25°C.
Al(s) ∣ Al3+(aq, 0.115 M) ∣∣ Al3+(aq, 3.89 M) ∣ Al(s)
A) +1.66 V
B) +0.060 V
C) 0.00 V
D) +0.090 V
E) +0.030 V
47) Identify the battery that is in most automobiles.
A) dry-cell battery
B) lithium ion battery
C) lead-acid storage battery
D) NiCad battery
E) fuel cell
48) Identify the battery that is used as a common flashlight battery.
A) dry-cell battery
B) lithium ion battery
C) lead-acid storage battery
D) NiCad battery
E) fuel cell
49) Identify the components of a fuel cell.
A) nickel-metal hydride
B) lithium ion
C) hydrogen-oxygen
D) nickel-cadmium
E) zinc-manganese
50) Identify the battery type that has a high overcharge tolerance.
A) NiCad
B) Li ion
C) NiMH
D) lead storage
E) none of the above
51) What is the reaction at the anode in a breathalyzer?
A) Ethanol is oxidized to acetic acid.
B) Acetic acid is reduced to ethanol.
C) Oxygen is reduced.
D) Hydrogen is oxidized.
E) Ethanol is oxidized to acetaldehyde.
52) What is the reaction at the cathode in a breathalyzer?
A) Ethanol is oxidized to acetic acid.
B) Acetic acid is reduced to ethanol.
C) Oxygen is reduced.
D) Hydrogen is oxidized.
E) Ethanol is oxidized to acetaldehyde.
53) Describe how water can be a good conductor of current.
A) use pure water
B) heat the water
C) add salt
D) chill the water
E) vaporize the water
54) What mass of silver can be plated onto an object in 33.5 minutes at 8.70 A of current?
Ag⁺(aq) + e⁻ → Ag(s)
A) 19.6 g
B) 0.326 g
C) 9.78 g
D) 3.07 g
E) 0.102 g
55) What mass of aluminum can be plated onto an object in 755 minutes at 5.80 A of current?
A) 73.5 g
B) 24.5 g
C) 220. g
D) 147 g
E) 8.17 g
56) Nickel can be plated from aqueous solution according to the following half reaction. How long
would it take (in min) to plate 29.6 g of nickel at 4.7 A?
Ni2+(aq) + 2 e⁻ → Ni(s)
A) 1.7 × 102 min
B) 5.9 × 102 min
C) 3.5 × 102 min
D) 4.8 × 102 min
E) 6.2 × 102 min
57) Describe the reactions during the electrolysis of water.
A) Oxygen is reduced and hydrogen is oxidized.
B) Oxygen and hydrogen are both oxidized.
C) Oxygen and hydrogen are both reduced.
D) Oxygen is oxidized and hydrogen is reduced.
E) Neither oxygen or hydrogen are oxidized or reduced.
58) Identify a component in the formation of rust.
A) salt
B) moisture
C) acid
D) all of the above
E) none of the above
59) To prevent rust, nails are coated with ________.
A) zinc
B) salt
C) calcium
D) sodium
E) lithium
60) Predict the species that will be reduced first if the following mixture of molten salts undergoes
electrolysis.
Na+, Ca2+, Cl⁻, Br⁻, F⁻
A) Na⁺
B) Cl⁻
C) Ca2+
D) Br⁻
E) F⁻
61) Predict the species that will be reduced first if the following mixture of molten salts undergoes
electrolysis.
Zn2+, Fe3+, Mg2+, Br–, I–
A) Zn2+
B) Mg2+
C) Br–
D) Fe3+
E) I–
62) Predict the species that will be oxidized first if the following mixture of molten salts undergoes
electrolysis.
Cu2+, Mg2+, Cl⁻, Br⁻, F⁻
A) Cl⁻
B) F⁻
C) Cu2+
D) Mg2+
E) Br⁻
Algorithmic Questions
1) Identify oxidation.
A) increase in oxidation number
B) loss of electrons
C) gain of protons
D) loss of neutrons
E) both A and B
2) What element is being oxidized in the following redox reaction?
Mg2+(aq) + NH4+(aq) → Mg(s) + NO3⁻(aq)
A) Mg
B) N
C) H
D) O
3) Balance the following redox reaction if it occurs in acidic solution. What are the coefficients in front
of Ni and H+ in the balanced reaction?
Ni2+(aq) + NH4+(aq) → Ni(s) + NO3⁻(aq)
A) Ni = 1, H⁺ = 8
B) Ni = 1, H⁺ = 4
C) Ni = 4, H⁺ = 10
D) Ni = 2, H⁺ = 4
E) Ni = 3, H⁺ = 5
4) Balance the following redox reaction if it occurs in acidic solution. What are the coefficients in front
of Sn and Ag+ in the balanced reaction?
Sn(s) + Ag+(aq) → Ag(s) + Sn2+(aq)
A) Sn = 1, Ag⁺ = 2
B) Sn = 1, Ag⁺ = 1
C) Sn = 2, Ag⁺ = 1
D) Sn = 2, Ag⁺ = 2
E) Sn = 3, Ag⁺ = 1