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Failure to oxidise Fe 2+ to Fe 3+

  1. Jun 26, 2015 #1
    Hi all,

    I have a problem which is quite basic, and I must be missing something.
    Fe 3+ + e > Fe 2+ +0.77v
    O2 + 4H+ + 4e > 2H2O +1.23v

    Re arranged, this tells us that if we bubble air through iron 2 sulphate solution, acidified with H2SO4, the oxygen should oxidise the Fe 2+ to Fe 3+ using the protons from the sulphuric acid. Many texts also say this. However, when I put approx. 10g of green iron 2 sulphate heptahydrate into about 150ml water and add about 6 ml of c.H2SO4, and bubble air through it from a fish tank aerator, it stays green, and does not go orange as one would expect. How is this?

    My project is quite simple. I want to generate Fe 3+ to dissolve metals like copper. It is a good agent to do this, but on reflection, could I not dissolve the copper directly, as the oxidation potential is easily high enough. Or would there be a rate problem?

    Any suggestions would be greatly appreciated.
  2. jcsd
  3. Jun 26, 2015 #2


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    Staff: Mentor

    I would plug the concentrations into Nernst equation to see where you are - potentials you listed are standard ones, formal will be different.

    As far as I know best way of oxidizing Fe2+ for etching is done with H2O2 in HCl.
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