Reduction Potentials

[teenup91]

Does the MCAT always give a reduction potential table, or are there cases where it gives an oxidation potential table?

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[mikil100]

They could end giving a mix I would assume as the oxidation and reduction are just flipped signs.

I have seen questions where some are gaining and some are losing electrons in the same table. Just keep tracking of what is being reduced and what is being oxidized and the signs for each

 

[Altius Premier Tutor]

It would be the first time I've every seen it, but "something a little different" is kind of what they like to do. If you're a memorizer, that can be dangerous, but if you understand it doesn't matter. Larger, more positive or less negative E values mean the specie on the reactant side of the half-reaction wants to be reduced relatively more than whatever you are comparing to ; Lower, less positive or more negative E values mean the specie on the reactant side of the half-reaction wants to be reduced LESS than what you are comparing to, so it will be oxidized in that pair. Great electrochemistry take homes:

1. Flipping the half-reaction flips the sign of the E value

2. oxidation to reduction or vice versa flips the sign of the E value

3. NO STOICHIOMETRY! For the Hess's Law half-reactions in genchem you must multiply the deltaG, deltaH or entropy by the coefficient, but with electrochem the E is whatever it is no matter how many moles of electrons.

4. REDOX = PAIRS ONLY: There has to be two (2) things! It's either a cell connecting two solutions/ions or its two species in a RXN. ONE thing never does REDOX anything; so if something is happening (i.e., X is getting reduced), the opposite is happening to someone else (something called Y has to be getting oxidized. The electrons have to come from some where, we aren't creating matter!) If I had a penny every time a student started talking about Fe3+ or Cu+ "doing REDOX" With whom I ask? What do you mean? they say...

 

[chemtopper]

Does the MCAT always give a reduction potential table, or are there cases where it gives an oxidation potential table?

You need to look half reactions ...if it is a half reaction in which electrons are gained then reduction potential is given next to it and if oxidation reaction is given then oxidation potential is given ...

 

[Altius Premier Tutor]

Does the MCAT always give a reduction potential table, or are there cases where it gives an oxidation potential table?

It may help you to realize that I don't think "oxidation potential" is actually an accepted term. I always see it called either "oxidation-reduction potential" or "reduction potential." The precise term is "Standard Reduction Potential." So, an oxidation half-reaction will still have a "Standard REDUCTION Potential," it will just have a smaller positive or more negative reduction potential than whatever it is exchanging electrons with. Remember too, that the same specie can (i.e., Fe2+) can go either way (oxidation or reduction), but it always has the same "Standard REDUCTION Potential." What it does depends on who it is paired with. It will lose some fights (Oxidation, someone stole my electrons who was stronger than me [he had a more + E than me]) and win some fights (Oxidation, I stole these electrons from someone cuz I was stronger than he was [he had a less +E than me]).