SuperOxide
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Weird vapour forming above [pretty pure] white phosphorus sample in water
This is probably something very simple and obvious that Ive just never heard of before and didn't find via Google.
I have a sample of white phosphorus that I purchased from LabDirect, and it definitely seems rather pure (I go by the color and the word of the
vendor). I store it under distilled water in a vial covered with aluminium foil. Today I took it out (only been in the vial for a couple weeks) and
noticed a weird white vapour has formed above the water.
It obviously can't be P2O5 or else it would have reacted with the water to form the acid. It doesn't seem to do anything when I shake the vial around.
I haven't opened it yet.
Heres an image (and more here):
Anyone know what this could be? Very curious. I've asked around and nobody seems to know.
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Rainwater
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No clue. But a quick google turned up nothing.
It's time to make assumptions.
You have water in their most likely contamination could be gas, (co2, o2) or minerals (MgSO4, NaCl)
The bottle could have been improperly cleaned, so let's add soap (NaOH, KOH, NaHCO3)
Cl- would make HCl, which can cloud up like that.
These are just guesses
"You can't do that" - challenge accepted
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woelen
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Most likely it is smoke from oxidation of the white phosphorus. I also noticed this with my sample. Initially, the air in the bottle contains a little
O2, and this oxidizes the phosphorus, giving white smoke. If you take out a piece of white P, then you actually see smoke coming from the piece of
white P. This smoke slowly dissolves in the water and when the concentration of the oxygen becomes lower, the nature of the smoke changes (from P4O10
to P4O6, and finally even lower, ill-specified, suboxides are formed). Finally, the4re is no oxygen left, and no more fumes will form. In the final
situation, there may be a thin film of yellow brown stuff on the surface of the water in the bottle, which is some mix of suboxides of phosphorus,
insoluble in water. After this initial change, no more changes occur, until you open the bottle again. Then new fresh O2 can go in, and again a little
amount of your white P is oxidized.
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Herr Haber
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I saved about a gram of impure, reclaimed white P. Something deposited on the edges of the glass at the water level and it looks as if there was
"snow" (white P specks I assume) around the main globule.
Heat the closed vial to 50c for a start and see what happens. Your sample will change shape though.
Or open it underwater and simply top it up.
The spirit of adventure was upon me. Having nitric acid and copper, I had only to learn what the words 'act upon' meant. - Ira Remsen
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SuperOxide
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Quote: Originally posted by Herr Haber  |
Heat the closed vial to 50c for a start and see what happens. Your sample will change shape though.
Or open it underwater and simply top it up. |
I don't wanna heat it up :-( It looks like heating it up causes it to change color to a darker yellow (red phosphorus I assume), and since this is
just a sample for my element collection, I'd like it to remain nice and clean.
However... I do have 25g of white phosphorus that should arrive here on Monday ;-) So maybe if the same thing occurs with that sample, then I'll heat
it up as you suggested and see what happens.
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Herr Haber
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By just melting underwater it will shed its skin if it's red / orange-ish or has trapped some other crap.
"Pan" it, roll it to the other side of the beaker and it will solidify white and clean upon cooling.
Be super careful when heating. Blobs of WP will float to the surface, burn and you'll have impure phosphorus again. Not to mention the danger.
Anyway, 25 grams will give you a lot more experience than I have and I'm not sure that would solve your original problem.
The spirit of adventure was upon me. Having nitric acid and copper, I had only to learn what the words 'act upon' meant. - Ira Remsen
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AJKOER
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Covering chemicals with Al foil is not recommended.
In the case of using Al foil to seal a glass vessel exposed to NO2, the unexpected creation of anhydrous Aluminum nitrate (as reported on SM). See
Wikipedia https://en.wikipedia.org/wiki/Nitrogen_dioxide on NO2 to quote:
"Conversion to nitrates
NO2 is used to generate anhydrous metal nitrates from the oxides:[10]
MO + 3 NO2 → M(NO3)2 + NO "
where we are now substituting for nitrogen, the element phosphorous.
So my guess here, the creation of an anhydrous Aluminum salt like phosphate which has a framework structures similar to zeolites from chemical
interactions with air.
Actually, a nice incidental experiment!
Note, Al foil used to encase your candy is only inert due to a thin acrylic coating and regular rolls of Al wrap are heat treated for added Al2O3
protective coating, but this is not sustainable, as even such common things as salted vinegar in a sandwich wrapped with Al will produce a visible
reaction with the aluminum foil over a course of days.
[Edited on 6-2-2022 by AJKOER]
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Texium
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Oh come on, that is obviously not what is happening here. woelen already gave a clear explanation that makes a lot more sense.
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SuperOxide
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| Quote: Originally posted by Texium | | Oh come on, that is obviously not what is happening here. woelen already gave a clear explanation that makes a lot more sense. |
I just have a hard time understanding why any phosphorus oxides wouldn't immediately get dissolved into the water..
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AJKOER
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My speculation relates (and, I definitely do consider it as a conjecture) follows from the statement by Woelen, to quote:
"Most likely it is smoke from oxidation of the white phosphorus. I also noticed this with my sample. Initially, the air in the bottle contains a
little O2, and this oxidizes the phosphorus, giving white smoke"
And further, the comments by Superoxide:
"Today I took it out (only been in the vial for a couple weeks)...It obviously can't be P2O5 or else it would have reacted with the water to form the
acid."
So possibly a slow reaction path.
All of which is at least suggestive of possibly paralleling the slow action of NO2 with Al that leads to an Aluminum salt. This is just an option that
apparently has not be mentioned, and is interestingly, apparently as unexpected as was the action of fumes containing NO2.
Having been proposed, an option on the list of possibilities to be affirmed or negated.
[Edit] A simple test: Capture a sample and add to dilute NH3 (aq). If you can a precipitate, consistent with an Al ion, it is an Aluminum salt as the
alternative, (NH4)3PO4, is water soluble.
[Edited on 6-2-2022 by AJKOER]
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SuperOxide
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So I definitely think that Woelen is right, since it looks like the sample I got today does the exact same thing when put into a glass vial, forming
the same vapour. I guess it just seems odd that an oxide of phosphorus would form above the water instead of just reacting with the water (especially
when shaken around a bit).
But, just for your viewing pleasure...
 
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timescale
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Wow, that's a beautiful sample you've got there. Wonder how it tastes 
Est-il une beauté aussi belle que le rêve ?
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Herr Haber
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Do a little experiment:
Pick a few specks after cutting or break them off. You just need a little. Put inside a beaker, heat to low boil.
Bubbles will carry the molten white P which will burn when it reaches the surface.
There should be orangy / redish stuff left, leading me to believe Woelen is probably right.
The spirit of adventure was upon me. Having nitric acid and copper, I had only to learn what the words 'act upon' meant. - Ira Remsen
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