LSD25
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Funny crystals forming - what are they?
I wonder what frozen ice-type crystals are formed when SO2 is passed into water and then the formed sulfurous acid is then frozen in a household
refrigerator?
The smell changes, and the crystaline substance is not soluble in the sulfurous acid - until the temperature of the solution is raised to near ambient
temperature.
What precisely could it be?
It is rather unlikely to be sulfurous acid, at least I'd imagine so...
It is similarly unlikely to be sulfur dioxide as it is a liquid from -10C and is somewhat soluble in sulfurous acid at nearly every temperature range
I can think of...
So, is it the oxidised variant of SO2 (I dare not type its name at present)? Does anyone know, offhand, if the frozen at near room temp,
oxidised-variant-of-SO2, is particularly soluble in sulfurous acid?
Help me with this please, I have two flasks half full of whatever the fuck it is right now (this is a photo of the same in the flask at between about
5-10C).
PS Can someone tell me how to cut the picture size down?
[Edited on 11-3-2008 by LSD25]
Whhhoooppps, that sure didn't work
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not_important
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Possibly a clathrate water-SO2
http://pubs.acs.org/cgi-bin/abstract.cgi/jpcafh/2004/108/i10...
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LSD25
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Is it possible to get that article, I'd kinda like to see how they act - I just tried filtration - the crystal's did melt (well above 0C) - the
formation of the crystals (I'll call 'em that cos that's how they behave) is fairly stock standard - they form a feather like formation of long needs
arranged parallel to one another. The only problem I have with the clathrate suggestion is that I'd have expected the volume of the clathrate formed
not to be getting larger with each freeze-thaw cycle (as this appears to be doing so far). I am also supprised at the fact that the initial formation
of them appears to occur more and more quickly each time the solution is cooled.
[EDIT]
I have altered the amount of time of the freezing cycle to 3 hours from 1 - this was because the freezing cycles are supposed to cause complete
solidification and at -10C this does not happen with this volume in one hour.
I also think I may have found the answer, although I have not seen the crystals described as a 'clathrate' per se, they appear to be precisely that:
http://www.austherm.com.au/hydrate.html
http://pubs.acs.org/cgi-bin/abstract.cgi/jacsat/1954/76/i14/...
What I find interesting is that this hydrate coexists with the supposed H2SO3 in the solution, as is shown by the increase in the crystal size and the
volume of the hydrate precipitated on each partial freeze and thaw cycle. This may offer a way of quickly reducing (and thus concentrating the acid)
sulfurous acids to strong sulfurous acids.
Oh yeah, I forgot to mention, this is the paper I am trying to replicate - sorta made harder than it has to be by my inability to comprehend japanese:
http://www.jstage.jst.go.jp/article/nikkashi/2001/2/2001_125...
The first thaw after the 3 hour cycle showed less of the clathrate/hydrate than any previous 1 hour freeze - it appears that the freezing of the
entire solution somehow affects the quantity and size of the clathrate/hydrate crystals grown.
[Edited on 11-3-2008 by LSD25]
Whhhoooppps, that sure didn't work
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PHILOU Zrealone
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Maybe SO2 hydrate... xSO2.yH2O
Many acid and compounds do have crystalline hydrates that display different boiling points but also different melting points…
Must be the case here with SO2.
The famous case of CH4 hydrate comes to mind…it is a white snowy solid burning with a purple flame with a much higher mp than methane.
[Edited on 11-3-2008 by PHILOU Zrealone]
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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not_important
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gas hydrates are clathrates, specifically containing just the gas and water. Discovered by Davy around 1810, Faraday use the chlorine clathrate in
his liquefaction of chlorine. Hydroquinone and thiourea are other clathrate forming molecules.
What might be causing the growth on thermal cycling is an increasing amount of SO2 ending up in the clathrate, perhaps seeded by crystal 'ghosts'
(often when something is crystallised, nanocrystallites survive the remelting of the crystals provided the temperature is not raised too high)
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bfesser
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What are they? Blurrynium oxide?
[Edited on 3/11/08 by bfesser]
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LSD25
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Finally defrosted after the third 3 hour freeze period - know I am really fucking amused - the clear crystals which melt at room temp are gone - but
they have been replaced by a thin layer of white powder at the bottom of the solution which no longer smells of SO2 but is still quite acidic.
I strongly suspect that the white powder is the residual calcium from the water used - it did not precipitate with sulfurous acid, but if I am right
and the paper is factual, the oxidation of the sulfurous acid to sulfuric acid would have been sufficient to cause the precipitation of the calcium
sulfate.
So, from that minor basis, I suspect that the reaction worked - I'll now test the assumption with calcium hydroxide of course but that is ok.
What did suprise me was that although a number of papers tend to suggest that the SO2.hydrate is actually the sulfurous acid itself, nobody has
mentioned this phase-forming behaviour when discussing this article. Despite the fact that the acidity of the solution is now pretty much what I
expected, it appears that my inability to read japanese script has led to a seriously confusing reaction
As far as I am concerned this is a very useful route to H2SO4, which is what I was after (it ain't so easy to get here).
PS I'd have to agree not_important, but I am still stumped how the crystal ghosts continue to exist even when the solution is thawed and vigorously
stirred. The only thing I can think of is that the putative H2SO3 is the clathrate forming compound - perhaps the other SO2 in the solution is simply
dissolved... Alternatively, perhaps the SO2.H2O clathrate is an intermediate between the H2SO3 and the H2SO4 formed by the dissolved oxygen? Does
anybody actually 'KNOW'?
PPS Actually it appears that this was the first clathrate/hydrate discovered by Priestley in 1778, describing anomolous ice formation at ambient
temperature which sank in aqueous SO2 solution...http://tinyurl.com/26ntvs
Whhhoooppps, that sure didn't work
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not_important
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| Quote: | Originally posted by LSD25...
I strongly suspect that the white powder is the residual calcium from the water used... |
You're not using distilled/deionised water for this early stage? Could give real confusing result.
| Quote: | ...
What did suprise me was that although a number of papers tend to suggest that the SO2.hydrate is actually the sulfurous acid itself, nobody has
mentioned this phase-forming behaviour when discussing this article. Despite the fact that the acidity of the solution is now pretty much what I
expected, it appears that my inability to read japanese script has led to a seriously confusing reaction
...
PS I'd have to agree not_important, but I am still stumped how the crystal ghosts continue to exist even when the solution is thawed and vigorously
stirred. The only thing I can think of is that the putative H2SO3 is the clathrate forming compound - perhaps the other SO2 in the solution is simply
dissolved... Alternatively, perhaps the SO2.H2O clathrate is an intermediate between the H2SO3 and the H2SO4 formed by the dissolved oxygen? Does
anybody actually 'KNOW'?
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Gas hydrates/clathrates generally have several dozen water molecules making up the cage for each gas molecule, and have been shown to involve only Van
der Waals interactions, not proper bonds. That ratio range just seems too high to have anything to do with H2SO3, although the cage may be enclosing
a H2O.SO2 pair.
Stirring isn't going to affect the nano-crystallites much. And in readings on purification by crystallisation or controlled freezing, examples were
given where crystal structure seemed to exist for as much as 50 or 60 degrees above the melting point for substances melting in the range of 50 to 180
C. For almost all the examples. a variety of inorganic and organic compounds on a number of different surfaces, 10 degrees above the MP was the least
temperature that would 'erase' the memory, and in some cases had to be held for as much as an hour.
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LSD25
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| Quote: | Originally posted by not_important,
You're not using distilled/deionised water for this early stage? Could give real confusing result. |
 No. I was sitting at home bored and looking for something to do.... I remembered
this paper and thought, ah well that looks like it is not too difficult, I have the chem's and the equipment, yeah let's do it... I was out of
deionised water, so I used tap water - the principle idea being that I didn't have to buy anything (I get paid monthly - 3 days to go , one now ).
As to the increase in the volume of the clathrate on the first two or three freeze cycles, that is interesting and I promise to read up more on
that... As to the possibility that the clathrate is acting as an intermediate in the oxidation, I still regard this as a possibility - if the
oxidation is occurring during the freeze cycles and the clathrate is increasing then dissapearing in succesive freeze/thaw cycles, that would suggest
to me that the volume of the clathrate is somehow indicative of the progress of the oxidation (increases from nothing then decreases to nothing).
Seems logical to me anyhow?
Whhhoooppps, that sure didn't work
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