Dissolved oxygen related to redox potential

Rexmundi

I have read a little bit about some industries deaerating water used in boilers made of iron to prevent them from becoming damaged.

I think this is because removing dissolved oxygen from the water lowers its redox potential. I think that this works because once the redox potential of the surrounding environment is lowered past a certain point it is no longer possible for Fe+2 to oxidize into Fe+3.
Am I right about any of this?

I was also wondering about the reverse reaction, I have read a little bit about using electrolysis for this. If I had some other method of lowering the redox potential of the system far enough would the Fe+3 go back to Fe+2?

I'm sure I shouldn't be I'm sort of thinking of this as a parallel to melting point/boiling point.

Borek

I don't think potential plays important role here. Oxygen is an oxidizer strong enough to work on iron even in very low concentrations. It can be easily calculated from Nernst equation, at the moment I am only referring to my intuition. Call it an educated guess.

However, if you take a look at the reaction stoichiometry, it becomes obvious that amount of iron oxidized is limited by the amount of oxygen present. Less oxygen present, less iron oxidized.

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Rexmundi

Okay I see the oxygen as a limiting reactant idea now and that makes sense, it's simpler than I was making it out to be.

I'll try to restate the second part of my question.

If I had some Fe₂0₃ in an anaerobic solution could it change to Fe₃0₄?
Could it take an electron from H₂0 somehow?
Would it help if the redox potential of the solution was very low?

Sorry if this is nonsense, I have not taken a chemistry course in a long time and do not really know how these things work.

BryanTallant

The answer is not straightforward, but simple in that it would attempt to reach equilibrium:
Yes, it could steal things from water (O, H or electrons and break up an H₂O)
A solution of Fe₂O₃ would change some to Fe₃O₄ as needed to reach equilibrium

Your boiler situation is a little different, you are oxidizing zero-valent iron (Fe) to other states (both Fe²⁺ and Fe³⁺) depending on redox potential.