ScienceBum
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Breakup of solidified crystals
This is a question I feel really bad about asking, but I kind of have to since last time I destroyed my flask like an idiot..
So I noticed that when doing recrystallization of certain things (in this case aspirin) the crystals tend to stick to my glass like super glue,
especially if I don't break them up as they're forming(which I did not do this time). I've been taking a hammer and stir rod and trying to gently
chisel them away from the glass, especially on the bottom but it doesn't seem to be doing the trick..
So, even though I could probably heat this up enough to melt everything I'd like to know what you guys do to break up stuck crystals on your glassware
if that's not feasible, or if this is a non-issue for everybody except me let me know.. and thanks
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Tsjerk
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Doing this in a beaker instead of a flask already makes things easier
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JJay
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I usually just scrape them with a stainless steel spatula, and I try to avoid crystallizing things in flasks. When it is unavoidable, you can
sometimes loosen up solids with heat or solvent, and when all else fails, you can usually slowly grind them up with a stir rod. I have a hammer
sitting next to my glassware, but I would never consider hammering on it... it would be destroyed instantly. Even just scraping isn't good for it....
Breaking crystals up as they are forming can make things a lot easier.
Flasks get destroyed sometimes; it's unavoidable.
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aga
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Recalling, yet again, some wise words from blogfast25 :-
Boil your liquid down in a beaker then transfer to a disposable plastic container when it is cool enough/has not yet started to go solid.
When the crystals have formed, you can just squeeze the sides of the cup to easily release them.
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Ozone
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I'd re-dissolve, transfer to a beaker (or better, a large petri dish), and recrystallize it there.
Also, if you are to employ the "Solo* cup method," make sure, beforehand, that the plastic will resist the action of whatever solvent (and
temperature) you are working in. For aspirin, I imagine you are working in ethanol (max 78.4°C), which should be OK with polystyrene (but,
close--glass transition is at ~100°C--and many poor solvents are more effective than you'd think once you are near this temperature).
I'd recommend a small test first, removed from sources of heat/fire.
O3
*Interestingly: http://www.cnn.com/2016/12/29/health/red-solo-cup-death-trnd...
[Edited on 3-1-2017 by Ozone]
-Anyone who never made a mistake never tried anything new.
--Albert Einstein
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ScienceBum
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Okay , so I'm pretty sure I've isolated the source of the problem. I'll run some tests later if I have time, but if anyone else has done this before
or wants to give it a shot go for it.
I was using acetone as my solvent in this case, and just letting it slowly evap over a few days in a spare drinking glass I had lying around since it
had a wide mouth - not a beaker or a flask, sorry if I made that unclear. Before dissolving everything, I looked at the ingredients list on the
aspirin and there was really only one thing there that was evidently soluble besides the ASA. It was something called "triacetin", which is a triester
of glycerin according to wikipedia(and some other crap).
So my guess is, if that went along with the ASA that might have caused it to stick/fuse to the glass after recrystallizing. It's just a guess, but
because this is the same aspirin source I used last time, and the same problem occured that's all I can come up with.
In any case, if other people can replicate this problem then I would avoid using aspirin sources with triacetin in them, since it's pretty damn
soluble in everything and makes stuff stick like glue.
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Texium
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Thread Moved
3-1-2017 at 11:51 |
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