I don't know how to find an electrochemical's cell reduction potential.

Chimezuru_Iheukwum
Chimezuru_Iheukwum Posts: 7

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edited March 24 in MCAT Question of the Day
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I picked B because I learned for example 1 (on the right) that if we're given 2 reduction half reactions, we could get the oxidized half reaction's reduction potential by subtracting it. Thus, for B, I did "1.78V -(-0.32V)". Why am I wrong? Thank you!

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  • Jacob_Arulandu
    Jacob_Arulandu Posts: 192

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    I think the problem here is they gave you two reduction-half reactions. In this case, looking at answers A and D, we see that they have deliberately included some reactions that have an oxidation and a reduction pair which means that answers B and C probably aren't right because they don't form a pair of reactions. There are definitely some questions out there that may give you just the reduction potentials of two half-reactions and ask you based on a passage which would occur at the cathode (reduction) or anode (oxidation) and you would have to flip one of the reactions as you did to make a redox pair and find the option that would be spontaneous (galvanic) or nonspontaneous (electrolytic).

  • Ae-Ri
    Ae-Ri Posts: 342

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    Solid answer, Jacob! In actuality, you can make any of those sets of answers spontaneous as long as you've got a half reaction that's got a bigger reduction potential than the other, which is true for all four answers, so as Jacob mentions, you need to dig a bit deeper. Essentially, the question is asking you to understanding that two reactions that are both reduced (or oxidized) can't work. We need the thing being reduced to have a bigger potential than the thing being oxidized for a spontaneous process, which only works with the last answer choice.

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  • Jacob_Arulandu
    Jacob_Arulandu Posts: 192

    Hall of Fame

    🐐
    Answer ✓

    I think the problem here is they gave you two reduction-half reactions. In this case, looking at answers A and D, we see that they have deliberately included some reactions that have an oxidation and a reduction pair which means that answers B and C probably aren't right because they don't form a pair of reactions. There are definitely some questions out there that may give you just the reduction potentials of two half-reactions and ask you based on a passage which would occur at the cathode (reduction) or anode (oxidation) and you would have to flip one of the reactions as you did to make a redox pair and find the option that would be spontaneous (galvanic) or nonspontaneous (electrolytic).

  • Ae-Ri
    Ae-Ri Posts: 342

    Moderator

    🚨
    Answer ✓

    Solid answer, Jacob! In actuality, you can make any of those sets of answers spontaneous as long as you've got a half reaction that's got a bigger reduction potential than the other, which is true for all four answers, so as Jacob mentions, you need to dig a bit deeper. Essentially, the question is asking you to understanding that two reactions that are both reduced (or oxidized) can't work. We need the thing being reduced to have a bigger potential than the thing being oxidized for a spontaneous process, which only works with the last answer choice.

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