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Oxidation of iron

by tmiddlet
Tags: iron, oxidation
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Jan11-13, 08:47 PM
P: 26
I've got a question that is bugging me

If I have a concentrated sodium hydroxide solution and electrolyze it with iron electrodes, some of the possible reactions at the positive electrode are
2H2O -> O2 + 4H++4e-. Eo = -1.23 V
4OH- -> O2 + 2H2O + 4e-. Eo = -0.40 V
Fe -> Fe2+ + 2e-. Eo = 0.44 V

and at the negative electrode, the most likely reaction is
2H2O +2e- -> H2 +2OH-. Eo = -0.88 V

Given this information, I would expect to see hydrogen gas at the negative electrode and iron hydroxide at the positive, but when I actually perform it I get oxygen and hydrogen, but no iron hydroxide. Why is this?
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Jan12-13, 02:44 AM
Borek's Avatar
P: 23,538
Reactions occur in the order from the "easiest" to the "hardest" - so as long as there is water present it will react preferentially.
Jan14-13, 06:50 PM
P: 26
That's what I thought, but it is much easier to oxidize iron than either water or hydroxide according to the values I found... Why do I not get any iron hydroxide?

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