# Half cell potentials

1. Apr 8, 2010

### kooombaya

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. Apr 9, 2010

### 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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3. Apr 9, 2010

### kooombaya

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...

4. Apr 9, 2010

### 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

5. Apr 9, 2010

### kooombaya

Oh I see!! Thanks so much Borek!