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MCAT Chemistry Question — Strongest Reducing Agent

  • by John
  • Dec 26, 2014
  • MCAT Blog, MCAT Chemistry, MCAT Question of the Day

Given the list of reduction potentials, which of the following species is the strongest reducing agent?

 

Li+(aq)+ e–  →Li (s) Eored = -3.04 V

Zn2+(aq) + 2 e→ Zn (s) Eored = -0.76 V

Ag+(aq)  + e→ Ag (s) Eored = 0.80 V

Ce4+(aq)  + e→ Ce3+ (s) Eored = 1.44 V

 

A. Ce4+

B. Zn2+

C. Li

D. Ag

 

Explanation

 

This question is testing your understanding of the redox chemistry and reduction potentials. To answer this question, you must first know that a reducing agent is itself oxidized. Therefore, the strongest reducing agent is going to be the species that is most readily oxidized. The Nernst equation, DG = -nFE, shows that a spontaneous reaction (DG < 0) corresponds to an electrochemical potential, E, that is greater than zero.

 

Since Ce4+ is spontaneously reduced, choice A can be eliminated. Zn2+ is already in its oxidized form and therefore cannot be oxidized further making B the wrong answer. Considering answer choices C and D, you must reverse the reactions to find Eoox, which equals the negative of the reduction potential (Eoox = -Eored). Therefore, the oxidation of Ag(s) is a nonspontaneous reaction while the oxidation of Li(s) proceeds spontaneous with a potential of +3.04 V, making C the correct answer.

 

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