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Making Fe3O4

  1. Dec 9, 2005 #1


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    I am trying to make some Iron (II, III) oxide, Fe3O4.
    To do this, I used this procedure as a model,
    [By the way, the colors described are what a color blind person saw, so in reality, it might be somewhat different]
    I did two trials. The first try, I made a solution of Iron (II) Chloride by reacting steel wool with Hydrochloric acid. The result was a dark yellowish solution with some light green stuff at the bottom. I decanted the clear yellow solution off, and added water to try to dissolve the green precipitate, which then formed a yellow solution. I figured the green precipitate must have been undissolved FeCl2, that after adding more water then dissolved, so I mixed the two solutions together. Then, very unscientifically, I added about twice the volume of Radio Shack brand PCB etching solution (FeCl3). Now I had a solution of Iron (II) and Iron (III) Chloride. To this, I added an ample amount of household ammonia (unknown concentration, but no detergent so it says on the label).
    Theoretically, the Fe3O4 should have precipitated out, leaving Ammonium Chloride in solution. It did not; all I got was a brownish solution.
    After failing the first time, this time I decided to follow the instructions much more closely. I took some Iron (III) Chloride solution [same from above] and added steel wool to it. I waited for it to dissolve, leaving behind a smell, brownish solution with a little gunk left behind. I filtered it, and added some more Iron (III) Chloride to the mixture. To this, I added ample amounts of household ammonia. Again, nothing happened, I got the same brown solution as I did on my first try.
    Just for kicks, I got a powerful magnet and placed it near the bottom of one of the containers holding the brown solution to see if I could attract any magnetic particles of Fe3O4 that had happened to form, but unfortunately, nothing happened.
    It looks like I was successfully in producing an Iron (II) Chloride solution, so the problem I think must be the ammonia. I don’t know the concentration, but it is normal household “pure” ammonia (really Ammonium Hydroxide) that contains no detergent.
    What might be substituted instead for ammonia to make this work?
  2. jcsd
  3. Dec 10, 2005 #2
    Why don't you go to the beach with your powerful magnet instead?
  4. Dec 10, 2005 #3


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    That would be easier, but I dont have a beach (or similar location) anywhere near by.
  5. Dec 10, 2005 #4
    From the wikipedia article on Fe3O4:

    "Magnetite can be prepared in the laboratory as a ferrofluid in the Massart method by mixing iron(II) chloride and iron(III) chloride in the presence of sodium hydroxide."
  6. Dec 11, 2005 #5


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    Yep, the Sodium Hydroxide did it.

    While adding the NaOH crystals to the solution, I immediatly saw a black percipitate begin to form. Upon placing the magnet next to the container, the percipitate moved toward the magnet.

    Yet another wonderful use of NaOH, too bad my supplies keep dwindling.
  7. Dec 11, 2005 #6
    FeCl2 + 2FeCl3 + 8NaOH --> Fe3O4 + 8NaCl + 4H2O

    Is this the correct equation for this reaction?
  8. Dec 11, 2005 #7


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    That is the correct equation.

    I suppose kit goes through Iron Hydroxide to become Iron Oxide,
    2 NaOH + FeCl2 -> 2 NaCl + Fe(OH)2
    3 NaOH + FeCl3 -> 3 NaCl + Fe(OH)3

    Fe(OH)2 -> FeO + H2O
    2 Fe(OH)3 -> Fe2O3 + 3 H2O
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