AP®ChemistryCollege BoardExam QuestionsUnit 9: Applications of ThermodynamicsElectrochemical Cells

Electrochemical Cells (College Board AP® Chemistry)

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Electrochemical Cells

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Electrochemical Cells

11 mark

The difference between a galvanic cell and an electrolytic cell is that

  • a galvanic cell requires an external power source, while an electrolytic cell does not.

  • oxidation occurs at the anode in a galvanic cell and at the cathode in an electrolytic cell.

  • a galvanic cell produces electrical energy from a spontaneous reaction, while an electrolytic cell requires electrical energy to drive a non-spontaneous reaction.

  • the flow of electrons is from the cathode to the anode in a galvanic cell, but from the anode to the cathode in an electrolytic cell.

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21 mark

In an electrolytic cell used to electrolyze molten NaCl, what happens at the cathode?

  • Dissolution of the electrode.

  • Evolution of chlorine gas.

  • Oxidation of chloride ions.

  • Reduction of sodium ions.

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31 mark

An experiment is set up to determine the value of the Faraday constant by electrolyzing dilute sulfuric acid.

Which experimental measurement is not required to calculate a value for the Faraday constant?

  • Current

  • Temperature

  • Time

  • Volume

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41 mark

A student sets up a galvanic cell that has a Pt (s) electrode and a Cu (s) electrode. The half-reactions that occur at each electrode are represented in the table below.

Electrode

Half-reaction

Pt (s)

Cr2+ (aq) → Cr3+ (aq) + e-

Cu (s)

Cu2+ (aq) + 2e- → Cu (s)

Which of the following correctly describes what happens to the mass of each electrode as the cell operates?

  • The mass of the Cu (s) electrode increases, and the mass of the Pt (s) electrode remains the same.

  • The mass of the Pt (s) electrode increases, and the mass of the Cu (s) electrode remains the same.

  • The mass of the Cu (s) and Pt (s) electrodes both increase.

  • The mass of the Cu (s) and Pt (s) electrodes both remain the same.

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51 mark

CuCl2 (l) → Cu (l) + Cl2 (g)

In an electrolytic cell based on the reaction represented above, which of the following describes the process at the anode?

  • Chlorine is oxidized.

  • Chlorine is reduced.

  • Copper is oxidized.

  • Copper is reduced.

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6
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The Fe2+/Fe, Ni2+/Ni cell

The standard reduction potentials for the half-reactions related to the galvanic cell represented above are listed in the table below.

Half-reaction

Eo (V)

Ni2+ (aq) + 2e- → Ni (s)

-0.25

Fe2+ (aq) + 2e- → Fe (s)

-0.44

Which of the following gives the value of Ecello for the cell?

  • Ecello = −0.69 V

  • Ecello = −0.19 V

  • Ecello = +0.19 V

  • Ecello = +0.69 V

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7
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Zn (s) + Cu2+ (aq) → Zn2+ (aq) + Cu (s)

What is the standard Gibbs free energy change (ΔG°) for the above reaction at 25°C, given the standard cell potential is 1.10 V?

  • -106 kJ mol-1

  • -212 kJ mol-1

  • +106 kJ mol-1

  • +212 kJ mol-1

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81 mark

Half-reaction

Eo (V)

Ni2+ (aq) + 2e- → Ni (s)

-0.25

Au3+ (aq) + 3e- → Au (s)

+1.50

Based on the information in the table above, which of the following shows the cell potential and the Gibbs free energy change for the overall reaction that occurs in a standard galvanic cell?

  • Ecello = +1.75 V; ΔGo = -169 kJ mol-1

  • Ecello = +1.75 V; ΔGo = -1013 kJ mol-1

  • Ecello = +2.25 V; ΔGo = -217 kJ mol-1

  • Ecello = +2.25 V; ΔGo = 1302 kJ mol-1

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9
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A galvanic cell is constructed with a Zn electrode in 0.1 M Zn2+ solution and a Cu electrode in 0.01 M Cu2+ solution.

Given E°(Cu2+/Cu) = +0.34 V and E°(Zn2+/Zn) = -0.76 V, what is the cell potential at 25°C?

  • 1.04 V

  • 1.07 V

  • 1.13 V

  • 1.16 V

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10
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In an electrolytic cell, a current of 2.5 A is passed through a solution of CuSO4 for 30 minutes. How many grams of copper will be deposited at the cathode?

  • 0.02 g

  • 0.74 g

  • 1.48 g

  • 2.96 g

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11
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A current of 1.5 A is passed through molten AlCl3 for 2 hours. What volume of chlorine gas (measured at STP) is produced at the anode?

  • 0.02 L

  • 1.23 L

  • 1.25 L

  • 2.51 L

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12
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A galvanic cell has a standard cell potential of +0.76 V at 25°C. Assuming 2 electrons are transferred, what is the equilibrium constant for the cell reaction?

  • 7.1 x 1012

  • 5.1 x 1025

  • 2.6 x 1051

  • 1.6 x 1059

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13
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Which of the following electrolytic cells would give the greatest mass of metal at the cathode?

 

Current

Time

Solution

A.

1.0

750

1.0 M CuSO4 (aq)

B.

1.0

500

1.0 M CuSO4 (aq)

C.

1.5

250

1.0 M AgNO3 (aq)

D.

2.0

250

1.0 MAgNO3 (aq)

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    141 mark

    For the reaction

    2Ag+ + Cd → Ag + Cd2+

    the standard cell potential is +0.82 V.

    What is the equilibrium constant for this reaction at 45 oC?

    • 1.0 x 10-26

    • 1.6 x 105

    • 6.3 x 106

    • 9.8 x 1025

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    15
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    Half-reaction

    Eo (V)

    Hg2+ (aq) + 2e- → Hg (s)

    +0.79

    Cu2+ (aq) + 2e- → Cu (s)

    +0.34

    Sn2+ (aq) + 2e- → Sn (s)

    -0.14

    Mn2+ (aq) + 2e- → Mn (s)

    -1.18

    A standard galvanic cell is made using Sn-Sn(NO3)2 and Cu-Cu(NO3)2 half-cells. Which of the following modifications to the cell will cause the greatest increase in Ecello?

    Asume all solutions are 1 M.

    • Replacing the Cu-Cu(NO3)2 half-cell with a Hg-Hg(NO3)2 half-cell.

    • Replacing the Cu-Cu(NO3)2 half-cell with a Mn-Mn(NO3)2 half-cell.

    • Replacing the Sn-Sn(NO3)2 half-cell with a Hg-Hg(NO3)2 half-cell.

    • Replacing the Sn-Sn(NO3)2 half-cell with a Mn-Mn(NO3)2 half-cell.

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