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Half cell potentials

  1. Apr 8, 2010 #1
    Is Fe2+(aq) capable of reducing Sn2+(aq) to Sn metal?



    The standard reduction potentials from my book are -0.14 for Sn2+ and -0.44 for Fe2+



    Because Sn has a more positive Epot it has a greater tendency to be reduced. So add the Epot up: -0.14 + 0.44 (oxidation)= 0.3. It's positive so this reaction can occur. However my answer key says the opposite. Can someone explain please? Thanks.
     
  2. jcsd
  3. Apr 9, 2010 #2

    Borek

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    Staff: Mentor

    You are looking at the wrong potential for iron. -0.44 means iron gets reduced to metallic Fe, you want it to be a reducing agent - that means it has to be oxidized to Fe3+.

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  4. Apr 9, 2010 #3
    Borek wrote: You are looking at the wrong potential for iron. -0.44 means iron gets reduced to metallic Fe, you want it to be a reducing agent - that means it has to be oxidized to Fe3+.

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    Yes I know. Here's the way I have it set up:
    Fe --> Fe2+ + 2e Eox = 0.44V
    Sn2+ + 2e --> Sn Ered = -0.14V

    Adding the half reactions I get Ecell = 0.44-0.14 = 0.3 which is positive so the reaction goes. Apparently this is wrong though. I'm confused...
     
  5. Apr 9, 2010 #4

    Borek

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    Staff: Mentor

    You know you are wrong, yet you repeat the same mistake? You have selected wrong reaction for iron. If you have a solution containing Fe2+ and Sn2+ you can't get both reduced to metal at the same time. If one gets reduced, the other has to be oxidized.

    Try to write balanced reaction equation. Remember Fe2+ and Sn2+ are your rectants.

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    methods
     
  6. Apr 9, 2010 #5
    Oh I see!! Thanks so much Borek!
     
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