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I know iron can react with many solutions, but when I tried to mix iron powder together with permanganate or dilute sulphuric acid, the iron powder would not react and instead, it just float on the surface of the solution. I tried to stir it for several minutes but it seems doesn't work.

It is pure iron powder, can be attracted by magnet

How can I dissolve iron powder and let it become $\ce{Fe^2+}$ or $\ce{Fe^3+}$ ? (Just dissolve it is ok)

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    $\begingroup$ To float on the surface of a water solution (density slightly above 1) is quite a peculiar thing to do for iron (density 7.8). Isn't the powder stained with some kind of oil, by any chance? $\endgroup$ Apr 27 '16 at 17:44
  • $\begingroup$ @IvanNeretin I've seen iron filings do this, and stirring (with a magnetic stir bar, at least) isn't exactly the best way to break surface tension at the top of water. $\endgroup$ Apr 27 '16 at 19:28
  • $\begingroup$ Then we have to lower the surface tension. I think a little drop of acetone might help. $\endgroup$ Apr 27 '16 at 19:33
  • $\begingroup$ As far as the question goes, I don't think you're going to get it to dissolve without making $\ce{Fe^{2+}}$ or $\ce{Fe^{3+}}$. There may be some wierdo $\ce{Fe^0}$ complexes that would do it, but those would be the exception. I'm not even sure it would work at all. $\endgroup$ Apr 27 '16 at 19:44
  • $\begingroup$ what is the iron powder made of? just pure elemental iron in its various oxidation states? I don't know how iron bonds so I'm not sure if it exists elemental or not :/, but if I can get a little bit of information about this I think I can help with the dissolving problem $\endgroup$
    – Ryan
    Apr 27 '16 at 20:19
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I did some brief research and I saw that sulfuric acid can dissolve iron:

Fe(s) + H$_2$SO$_4$(aq) → Fe$^{2+}$(aq) + SO$_4$$^{2-}$(aq) + H$_2$(g)

Of course, this would leave sulfate ions and perhaps some precautions would need to be taken because of hydrogen gas production. If you absolutely cant have any sulfate ions, you could precipitate them out by adding barium or silver ions to the solution, but that would require extra work and introduce new ions to the solution. Also note, the iron ions should be aqueous in +2 state but I read that if there is oxygen in the system (which there naturally would be), some iron(II) can oxidize to iron(III).

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    $\begingroup$ dissolution of iron in diluted acid is painfully slow. $\endgroup$
    – permeakra
    Apr 27 '16 at 21:38
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The reaction of metallic iron powder with sulfuric acid solution is rather slow. But it produces at least some Hydrogen bubbles that are adsorbed against the iron powder. This may be sufficient for maintaining the iron powder at the surface of the solution.

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  • $\begingroup$ (+1) Still, back in 1783, Jacques Charles and associates filled balloons with hydrogen that they generated via the reaction of iron and sulfuric acid. Brave folks! $\endgroup$
    – Ed V
    Jan 21 at 20:24
  • $\begingroup$ @Ed V, Right. But Charles and Gay-Lussac used rather concentrated sulfuric acid : 70% if my memory is correct. With 2 molar solutions, as used in high school laboratories, the reaction is desperately slow. $\endgroup$
    – Maurice
    Jan 21 at 21:16
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    $\begingroup$ I fully agree about the slowness! I first did this reaction many years ago and it was pathetically slow. And impurities in the iron powder I used made a nasty smell. Whenever I needed hydrogen gas in my basement chemistry lab, I used either zinc or manganese with non-concentrated sulfuric acid. Or I used aluminum granules with NaOH (fairly concentrated). Lucky I never had a major incident! ;) $\endgroup$
    – Ed V
    Jan 21 at 21:57
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    $\begingroup$ @Ed V. I agree with you. And even pure zinc does not react as quickly as desired. It is better to add a few drops of cobalt chloride solution. This produce an electrical cell effect, and the reaction becomes tumultuous. I give you 1 point. $\endgroup$
    – Maurice
    Jan 21 at 22:09
  • $\begingroup$ Ah, many thanks for the cobalt chloride tip! $\endgroup$
    – Ed V
    Jan 21 at 22:35

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