I was experimenting/playing with about 3cc of elemental iodine in a test tube,
melting, vapourisation, sublimation etc.
After I'd played enough, I melted all of the iodine and poured it out into a small stainless steel cup.
A little was lost as I didn't expect the liquid iodine to be so mobile / low viscosity /'runny'
About 2cc of iodine coated the inside of the cup with a very hard smooth layer, with the appearance of good dark chocolate.
When I inspected the cup two days later I found an aqueous looking dark liquid,
I've not read of elemental iodine being deliquescent - so what is the liquid?
How should I test it - for what ? woelen - 12-8-2015 at 01:05
The iodine reacted with the steel and the resulting compound absorbed water.
Fe + I2 --> FeI2
FeI2 is deliquescent. The dark color is due to unreacted iodine, which reacts with iodide ions to form dark brown I3(-) ions, which also dissolve in
the absorbed water. So, you have a mix of Fe(2+) ions, I(-) ions, I3(-) ions and most likely also some ferric oxide and hydroxide. Your iodine and
steel cup are spoiled.Sulaiman - 12-8-2015 at 04:12
thanks woelen,
I have more iodine and stainless steel cups, not worried about that,
(and as an exercise I shall see how much I2 I can simply recover)
I just did not expect ANY reaction between dry steel and liquid iodine ...
a new factoid.
So, the FeI2 acts like KI which I am familiar with (Logol's Iodine etc.) regarding the formation of the I3- ion,
then deliquescence 'feeds' the reaction with water?
I suppose that there must be many similar metal-halide analogues.
I might have guessed at that, but I could not imagine the effectively solid state reaction between steel and iodine,
... there is a battery in this somewhere ...
(and runaway reaction cells would make such pretty 'smoke') Magpie - 12-8-2015 at 12:41
Whenever I make Cl2 I know that the stainless steel floor in my hood is going to have corrosion blotches no matter how careful I am. I have to remove
these with a 3M Scotch-Brite scrub pad.
It seems that halogens readily attack stainless steel. I was warned about that when I showed my new stainless steel sink in a forum post. vmelkon - 14-8-2015 at 07:14
So, the FeI2 acts like KI which I am familiar with (Logol's Iodine etc.)
The reaction is between the I- ion and I2, so the metal ion doesn't play a role.
Also, leaving iodine out in the air is not a good idea. It sublimes away. A 1 mg crystal disappears in an hour. You need a jar with a good seal or put
it in a test tube and melt and close the glass.AJKOER - 16-8-2015 at 10:17
"An aqueous solution of ferrous iodide is readily prepared by warming iron filings and iodine together in water, when a colourless solution is
obtained. This, however, is not stable in air, as it absorbs oxygen, liberating free iodine. If a little sugar be added to the clear solution,
oxidation is retarded, and the crystalline pentahydrate, FeI2.5H2O, may be isolated."
"Ferric iodide, FeI3, has not as yet been prepared, but the possibility of its existence is perhaps indicated by the fact that hydrated ferric oxide
dissolves in hydriodic acid, yielding a brown solution."
So the brown solution may also be, per our Russian source, Fe(OH)I2 from Ferrous iodide in the presence of water and oxygen, and, I suspect, an excess
of Iron (our cup in this case). The amount of hydration and corresponding pH is likely also a factor as it relates to the particular Iron species
presence on oxidation of the Ferrous iodide.
-------------------------------------------------------
[Edit] Found another (albeit a dated source which I find particularly good in reporting actual observed chemistry independent of theory), "Elementary
Chemistry: With Special Reference to the Chemistry of ..., Volume 1, by Harry Mann Gordin, available at
https://books.google.com/books?pg=PA342&lpg=PA342&dq=ferric+hydroxide+iodide+(III)&sig=jlcZWpUtoA89b30h6j6Dc_nlJ1A&id=FgfnAAAAMAAJ&
;ots=4TJqVK-SD2#v=onepage&q=ferric%20hydroxide%20iodide%20(III)&f=false . To quote from page 342:
"Ferrous Iodide Fel2 is made by the direct interaction of the elements. It is a greenish-gray substance, easily soluble in water. A tetrahydrate
FeI2.4H20 can be obtained in pale-green crystals by recrystallizing the salt from water. The iodide is not stable, readily changing under the
influence of air and moisture to ferric hydroxide with liberation of iodine: 2FeI2 + 30 + 3H20 = 2Fe(OH)3 + 4I. The addition of sugar considerably
increases the stability of the iodide. A mixture of ferrous iodide and sugar is used as "saccharated ferrous iodide," and a solution of the iodide in
simple syrup is used as syrup of ferrous iodide. To further increase the stability of the syrup a little hypophosphorous acid is added to it (cf. p.
203).....Ferric Iodide Fel3 is not known in solid form. By dissolving iodine in a solution of ferrous iodide solutions are obtained which may contain
Fel3 or FeI2.2Fel3. A solution supposed to contain the latter is used for making potassium iodide (q. v.)."
So now with have a suspension of Fe(OH)3 in Iodine water. As the latter can react to a limited extent as follows (among other things, see Woelen
comments above):
I2 + H2O = HI + HOI
And as, FeI3 is apparently not formed due to stability issues (unfavorable thermodynamics, see http://link.springer.com/article/10.1007/s11224-010-9713-8 ), this still leaves HOI to react. As I have previously recounted on SM dated sources
suggesting the possibly related reaction of HOCl on Cu(OH)2 describing the formation of an unstable hypochlorite which subsequently decomposes
producing an oxychloride (see http://www.sciencemadness.org/talk/viewthread.php?tid=29522#... ), a similar path may exist here where the HOI acting on Fe(OH)3 is the first step
in the eventual creation of the claimed Fe(OH)I2.
Another path, in my opinion, would be via the formation on an iodate from the disproportionation of the HOI. However, as iodate salts are generally
more stable, I would think that such a path is less likely here if one accepts the creation of the ferric hydroxide di-iodide itself.
A particularly interesting path based on more recent radical based chemistry is via Fenton like reactions where the H2O2 is supplanted by, for exampe,
HOCl, which occurs in biological systems. As a source, see "Fenton chemistry in biology and medicine*" by Josef Prousek available at https://www.google.com/url?sa=t&source=web&rct=j&... . To quote reaction 15 on page 2330:
"For Fe(II) and Cu(I), this situation can be generally depicted as follows [20,39],
Fe2+/Cu+ + HOX → Fe3+/Cu2+ + HO• + X- (15)
where X = Cl, ONO, and SCN. "
which, I would argue, could apply to HOI also (due to its rapid disproportionation to HIO3, which is a strong oxidizing acid in acidic solutions).
This would further promote the hydrolysis of the Iodine in water. The hydroxyl radical created could than possibly further react via hydrogen
abstraction or addition as follows in the presence of light (see "SUPPORTING INFORMATION Production of Gas Phase NO2 and Halogens from the Photolysis
of Thin Water Films Containing Nitrate, Chloride and Bromide Ions at Room Temperature" available at https://www.google.com/url?sa=t&source=web&rct=j&... ):
HOI + HO• → H2O + IO• (see reaction A81 with Br )
I2 + HO• → HOI + I (see reaction G117 with Cl )
I- + HO• → HOI (see reaction A141 with Cl )
and there could be further reactions between the above and Fe(OH)3 eventually resulting in the tenative creation of Fe(OH)I2.
