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Rust in test-tubes of HCl FeO or Fe3O4?

  1. Jun 3, 2009 #1
    rust in test-tubes of HCl FeO or Fe3O4??

    I am doing experiments on steel nails in HCl solutions with a pH of about 1.5 - 2.
    The rust is black in colour, and is not attached to the surface of the nails. It stays at the bottom of the test-tube. Is this FeO or Fe3O4. Why is it that the rust I am getting in solutions of just salt is not the same colour?. And why is it red and attaching to the nail?
  2. jcsd
  3. Jun 4, 2009 #2


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    Re: rust in test-tubes of HCl FeO or Fe3O4??

    It has a lot to do with coordination inorganic chemistry which depends on quantum mechanical explanations which relate the iron to the " field " of ligands around it to explain the color , you may want to start off with Crystal Field Theory.
  4. Jun 5, 2009 #3
    Re: rust in test-tubes of HCl FeO or Fe3O4??

    Maybe with HCl you get more Fe2+ ions, that don't have enough time to be oxidized by air oxygen into Fe3+. In the first case you would get FeO (black), in the second Fe2O3 (red).
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