MCAT General Chemistry Question 166: Answer and Explanation

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Question: 166

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.

Correct Answer: C

Explanation:

In the oxidation-reduction reaction of a metal with oxygen, the metal will be oxidized (donate electrons) and oxygen will be reduced (accept electrons). This fact allows us to immediately eliminate choices (B) and (D). A species with a higher reduction potential is more likely to be reduced, and a species with a lower reduction potential is more likely to be oxidized. Based on the information in the question, iron is oxidized more readily than those metals; this means that iron has a lower reduction potential.

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