Jackson
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Purple Iron Compound?
Hi, I recently prepared some iron (ii) sulfate and decided to mix a small amount with some ammonia solution. It resulted in a grey precipitate. the
solution produced a brownish precipitate on contact with the air. I observed a light purple film on top. It was of a similar color to iodine. It
slowly turned into the same brown stuff (probably iron oxides/hydroxides) after sitting over night.
What could it be?
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fusso
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Probably be thin (hydr)oxide film, like rainbowy thin oxide layer on metals tend to look like.
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Abromination
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I have noticed this phenomenon before and it it is probably a hydroxide film reflecting light.
If you are interested in purple iron compounds, try preparing iron salicylate. Its yellow as a solid but purple in solution, rather like permanganate.
List of materials made by ScienceMadness.org users:
https://docs.google.com/spreadsheets/d/1nmJ8uq-h4IkXPxD5svnT...
--------------------------------
Elements Collected: H, Li, B, C, N, O, Mg, Al, Si, P, S, Fe, Ni, Cu, Zn, Ag, I, Au, Pb, Bi, Am
Last Acquired: B
Next: Na
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phlogiston
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No answer for your question, but if we are talking about purple iron compounds:
(2-hydroxyethyl) ammonium thioacetate also forms a beautiful purple iron complex.
I've come across a solution of this being sold as a cleaning product for removing rust stains (it dissolves iron oxides and hydroxides).
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"If a rocket goes up, who cares where it comes down, that's not my concern said Wernher von Braun" - Tom Lehrer |
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woelen
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When iron(II) is added to a base, then you get a nearly white precipitate of Fe(OH)2. This, however, is very easily oxidized by oxygen from air and
then it turns grey. On further oxidation it becomes dark blue, almost black. This is a mixed iron(II)/iron(III) hydroxide. When it is even further
oxidized, then it becomes orange/brown, the end product, which is iron(III) hydroxide. The purplish color you observed may be due to formation of a
thin layer of a mixed iron(II)/iron(III) hydroxide, at the surface of the solution, where it is in good contact with oxygen from air. This color
quickly disappears again on further oxidation, leading to a brown layer of iron(III) hydroxide.
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markx
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The ferrate ion (FeO4-2) has a purple coloration much alike permanganate.
It will form under anodic conditions in alkaline solutions and is rather shortlived.
Exact science is a figment of imagination.......
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Jackson
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Thanks for the responses.
Woolen, the process that you said is exactly what I have observed. Grey precipitate, shiny blue-black or purple-black film, and then when the film is
broken, like by sloshing around, a brown residue is formed.
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AJKOER
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This is a link (https://pdfs.semanticscholar.org/f83d/d855e637c2cd9ad1f9e0b2... ) to a pdf explaining the pH dependent chemistry, title 'The effect of pH on the
kinetics of spontaneous Fe(II) oxidation by O2 in aqueous solution – basic principles and a simple heuristic description'.
Per page 2082, the reactions include the possible presence of the radicals .OH and .O2-. In the further presence of NH3 (producing also alkaline
conditions as noted in the opening thread) more stuff like .NH2 radical:
.OH + NH3= H2O + .NH2
And, from there the oxidation of .NH2 from O2 in a chain leading to NO2-,..
The first thing I would suggest is to repeat the experiment substituting a very small amount of NaOH for aqueous NH3 and see if the purple compound is
stilled created, which could limit the possible paths to the purple compound involving nitrogen compounds.
-------------------------------------------------------
As the superoxide radical presence is cited on page 2082, I have yet to verify the possibility of the following radical reaction in the presence of
the amino radical:
.NH2 + .O2- = NH2- + O2
which in aqueous conditions could reform NH3 and elevate pH:
NH2- + H+ (from water) --> NH3 ( + OH-, raising pH, see https://www.google.com/search?source=hp&ei=rI9VXPWQDcqK5... )
[Edited on 2-2-2019 by AJKOER]
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Jackson
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Wait, so iron (II) can oxidize ammonia to NO2?
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fusso
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Apparently AJKOER is speaking bollocks again
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AJKOER
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As some doubt my comments, an extract citing sources:
Quote: Originally posted by AJKOER  | Some theory suggests, to create nitrite/nitrate from ammonia, start by employing a hydroxyl radical generating mechanism including photolysis (see http://pubs.acs.org/doi/abs/10.1021/jp0349132 ), fenton and fenton-type reactions involving transition metals (discussed below), radiation
(microwave pulse), electrolysis, sonochemistry,...
Then, the action of the •OH on ammonia in the presence of dissolved oxygen (or employ H2O2) is claimed by one reference to proceed as follows:
NH3 + •OH → H2O + •NH2 (see Laszlo extract and link below)
•NH2 + O2 → NH2O2• (aminylperoxyl radical unstable) → NO + H2O (See , "On the aqueous reactions of the aminyl radical with molecular oxygen
and the superoxide anion", Table 2.1 at https://www.google.com/url?sa=t&source=web&rct=j&... )
Having formed some NO, in the further presence of a hydroxyl radical source generator and hydrogen peroxide the following reactions, for example,
could introduce the formation of NO2:
H2O2 + •OH → H2O + •HO2
•HO2 + NO → •OH + NO2 (see https://www.google.com/url?url=http://scholar.google.com/sch... )
or, as the net of last two reactions equals:
H2O2 + NO ---UV or Fe(++), Cu(+), Co(++),..→ H2O + NO2
And further:
NO2 + H2O → HNO2 + HNO3
which introduces aqueous nitrite that is a better light induced promoter of hydroxyl radicals then nitrate, which is superior to H2O2. In the presence
of uv, strong solar light or select transition metals, this postulated reaction chain can likely accelerates the conversion of ammonia to
nitrite/nitrate. Interestingly, there are researchers reporting tissue cell damage from the seeming direct action of NO on H2O2 in biological systems
(see, for example, "Hydroxyl radical formation resulting from the interaction of nitric oxide and hydrogen peroxide.",by Nappi AJ, Vass E. ) although,
in my opinion, such a direct radical reaction need not take place given the enabling effects of light or transition metals. Note, my simple reaction
chain consumes and regenerates the very short lived hydroxyl radical which, in essence, could increase its apparent reactivity life span (as measured
by random cell collisions leading to cellular damage) having been, in effect, resurrected.
...........
[Edited on 16-9-2016 by AJKOER] |
Link to extract: http://www.sciencemadness.org/talk/viewthread.php?tid=30473 .
Note, I make no mention of the time frame involved in the conversion of ammonia to nitrite or the yield, so no claim on the practical nature of the
science. However, in the current context, the purple compound, while visible, is also likely at a very low concentration, assuming a possible nitrogen
based path (which I actually doubt).
[Edited on 2-2-2019 by AJKOER]
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Rhodanide
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Iron compounds with colors in the blue spectrum aren't entirely unheard of. Ferric Rhodizonate has a strikingly blue color in solution, however what
you've got is likely a mix of a bunch of things as opposed to one singular compound.
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