MCAT General Chemistry Question 169: Answer and Explanation

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Question: 169

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

Correct Answer: C

Explanation:

In an electrolytic cell, ionic compounds are broken up into their constituents; the cations (positively charged ions) migrate toward the cathode, and the anions (negatively charged ions) migrate toward the anode. In this case, the cations are H+ ions (protons), so option I is correct. Electrons flow from anode to cathode in all types of cells, meaning that option III is also correct. Option II is incorrect for two reasons. First, it is unlikely that the anions in any cell would be O2- rather than OH-. Second, and more significantly, these anions would flow to the anode, not the cathode.

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