MCAT General Chemistry Practice Test 12: Electrochemistry

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1. Rusting occurs due to the oxidation–reduction reaction of iron with environmental oxygen:

4 Fe (s) + 3 O2 (g) → 2 Fe2O3 (s)

Some metals cannot react with oxygen in this fashion.

Which of the following best explains why iron can?

  • A. Iron has a more positive reduction potential than those metals, making it more likely to donate electrons to oxygen.
  • B. Iron has a more positive reduction potential than those metals, making it more likely to accept electrons from oxygen.
  • C. Iron has a less positive reduction potential than those metals, making it more likely to donate electrons to oxygen.
  • D. Iron has a less positive reduction potential than those metals, making it more likely to accept electrons from oxygen.

2. Given the following standard reduction potentials:

What is the standard electromotive force of the following reaction?

Zn2+ + 2 Ag → 2 Ag+ + Zn

  • A. –2.2 V
  • B. –1.1 V
  • C. +1.1 V
  • D. +2.2 V

3. Consider the following data:

The anode of a certain galvanic cell is composed of copper. Which of the metals from the data table can be used at the cathode, assuming equal concentrations of the two electrolyte solutions?

  • A. Hg
  • B. Cu
  • C. Zn
  • D. Al

4. An electrolytic cell is filled with water. Which of the following will move toward the cathode of such a cell?

I. H+ ions

II. O2– ions

III. Electrons

  • A. I only
  • B. II only
  • C. I and III only
  • D. II and III only

5. If the value of E°cell is known, what other data is needed to calculate ΔG°?

  • A. Equilibrium constant
  • B. Reaction quotient
  • C. Temperature of the system
  • D. Half-reactions of the cells

6. Which of the following compounds is LEAST likely to be found in the salt bridge of a galvanic cell?

  • A. NaCl
  • B. SO3
  • C. MgSO3
  • D. NH4NO3

7. If the surface area of electrode material in an electrochemical cell is tripled, what else is necessarily tripled?

I. E°cell

II. Current

III. Keq

  • A. I only
  • B. II only
  • C. I and II only
  • D. II and III only

8. Which of the following can alter the emf of an electrochemical cell?

  • A. The mass of the electrodes
  • B. The length of the wire connecting the half-cells
  • C. The overall size of the battery
  • D. The temperature of the solutions in the half-cells

9. Which of the following statements could be true about a Na–Cd cell, based on the information below?

  • A. It is a galvanic cell, and sodium is the cathode.
  • B. It is an electrolytic cell, and cadmium is the anode.
  • C. It is a galvanic cell, with E°cell = 3.11 V.
  • D. It is an electrolytic cell, with E°cell = -3.11 V.

10. Which of the following expressions correctly describes the relationship between standard electromotive force and standard change in free energy?

  • A. ΔG° = -nF(E°red,anode - E°red,cathode)
  • B.
  • C.
  • D. ΔG° = nF(E°red,anode - E°red,cathode)

11. Which of the following choices is indicative of a spontaneous reaction, assuming standard condition?

  • A. E°cell is negative
  • B. Q = Keq
  • C. The cell is a concentration cell
  • D. Keq > 1

12. For a cell with the following half-reactions:

Anode: SO2 + 2 H2O → SO42- + 4 H+ + 2 e-

Cathode: Pd2+ + 2 e- → Pd

How would decreasing the pH of the solution inside the cell affect the electromotive force (emf)?

  • A. The emf would decrease.
  • B. The emf would remain the same.
  • C. The emf would increase.
  • D. The emf would become zero.

13. An electrolytic cell necessarily has:

  • A. ΔS° > 0
  • B. ΔG° < 0
  • C. Keq < 1
  • D. E°cell > 0

14. Which of the following is the best explanation for the fact that a larger mass of electrodes are required for lead–acid batteries, as compared to other batteries, to produce a certain current?

  • A. The lead–acid electrolyte, sulfuric acid, is diprotic and incompletely dissociates in solution.
  • B. The energy density of lead–acid electrodes is higher than that of other batteries.
  • C. The electrolytes in other batteries less readily dissociate than those of lead–acid batteries.
  • D. The energy density of lead–acid electrodes is lower than that of other batteries.

15. Which of the following best describes why over-charging a Ni–Cd battery is not detrimental?

  • A. The energy density of a Ni–Cd battery is high, so it can store more charge than other batteries per its mass.
  • B. The electrodes of a Ni–Cd battery can discharge through the circuit when they are fully charged.
  • C. The Ni–Cd battery will stop accepting electrons from an outside source when its electrodes are recharged.
  • D. Ni–Cd batteries have a high surge current and can dissipate the overcharge before damage can occur to electrodes.