AAMC Question Pack Chemistry Q. 4

[agurl1000]

Hey Everyone!

This may seem like a very basic chemistry topic, but I am pretty confused about it. The question asks for the best electron acceptor. I thought it would be Fe because it has a positive charge and will want an electron. But, the answer is S, because it is in the same column as O. Could someone explain to me what electron affinity is and why oxygen and sulfur are better electron acceptors? Also can iron be an electron acceptor too? Thanks!

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[aldol16]

Your first hint was that they specifically mentioned oxygen in the question stem, which means they're looking for something that is the most similar to oxygen. This is sulfur, since it's in the same group. Electron affinity is simply electronegativity. Electronegative elements want electrons and electropositive elements do not. Iron is not a good answer here because they're talking about junk iron, not oxidized iron. You're right in that iron in biological environments are used widely in redox roles (iron-sulfur clusters, etc.). But they're talking about junk iron here and not Fe(III) or Fe(II). Never just assume.