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  1. #1
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    Default best reducing agent question.. confused

    The most negative potential will will be the strongest reducing agent. Why doesnt this rule apply here?Click image for larger version. 

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    See question attached.

  2. #2
    Chad
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    First of all, the strongest reducing agent is the one that is most easily oxidized and therefore the one with the most positive oxidation potential. But as all the provided half-reactions were reductions you have to envision them all re-written exactly backwards with the signs on the potentials switched. The last part is realizing that a reducing agent has to be a reactant in an oxidation reaction. In looking at the relevant reaction backwards (as an oxidation) you can see that Cr2+ is the reactant that gets oxidized and therefore is the reducing agent, not Cr3+.

    To sum it up, in a table of reduction potentials, possible oxidizing agents should be chosen from chemical species on the lefthand side of the reaction arrow whereas possible reducing agents should be chosen from the righthand side of the reaction arrow (as written in the table of reduction potentials).

    Hope this helps!

  3. #3
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    This helps, but i need some more clarification.

    I've read that if you are given reduction potential table, you pick the one with the most negative potential. The one with the most negative potential = to the best reducing agent. Is this not true?

  4. #4
    Chad
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    To say that you pick the "one" with the most negative potential can be a little misleading but you do want to focus on the reaction with the most negative reduction potential. But there will be a reactant and a product in this reaction and only the product can act as a reducing agent (as it gets oxidized in the reverse reaction). The reason you're picking the reduction half-reaction with the most negative potential is that the reverse reaction will be the oxidation half-reaction with the most positive potential and therefore the most spontaneous oxidation. But it's the reactant in the reverse oxidation half-reaction (which is the product of the reduction half-reaction) that is the reducing agent.

    Let me know if this clears things up at all.

  5. #5
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    i think i got it. ? hopefully. just to make sure..

    so if you are given a table of reduction half reactions and asked to pick the best reducing agent, you want to reverse all the potentials and pick the most positive oxidation potential?

    vice versa if you are given a table of reduction half reactions and asked to pick the best oxidizing agent, you just look at the reduction potentials AS IS and pick the most negative potential?

    if you are given a table of oxidation half reactions and asked to pick the the best oxidizing agent- pick the most negative potential
    if you are given a table of oxidation half reactions and asked to pick the best reducing agent- pick the most positive potential

    and I really appreciate your explanations! they are very helpful.

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