KvantnaFizika
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Sulfuric acid purification
Hello to everyone, I'm glad to be on this, in my opinion, very professional chemistry forum.
Well, I have one totally amateur question, mainly because I'm clumsy  .
I've been doing something with my concentrated H2SO4, which is in one litre glass bottle, and I accidentally dropped my dropper with rubber bulb on
top. That rubber part happily dissolved in H2SO4, and the whole bottle of H2SO4 now all thick black.
Is there any way of filtrating/removing that carbon contamination?
Thank you
ĤΨ=EΨ
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hissingnoise
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You could try heating the acid to its boiling point to oxidise the contaminant!
Use a heavy pyrex casserole dish or similar and avoid inhaling the fumes . . .
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spong
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I remember there being a thread on cleaning up hardware store H2SO4 which was usually black/brown due to carbon impurities, assuming that most of the
black colour is from carbon (it may not be) then this could work:
http://www.sciencemadness.org/talk/viewthread.php?tid=3722
I still wouldn't rely on that acid for anything to impurity sensitive though, I have a 'dirty' bottle of HCl I use for things like that, it's pretty
much just an older bottle of it that I'm less careful about contaminating/conserving, I'd get some new acid and save this stuff after being cleaned
for uses like that.
If you've got the glassware you could distill it under vacuum but that's pretty risky business if you're new to chemistry.
Get some cheap-o plastic pipettes too 
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KvantnaFizika
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Thank you for quick replies, gentlemen. I'll try the oxidation way, but with smaller amounts because all my glassware is pretty old and
heat-unfriendly. If it does not work, H2O2 sounds obtainable.
I would really like to be able to buy new chemicals, but here in Croatia things are little bit harder than in the rest of the world  . But next time, I'll surely buy some plastic pipettes .
Well, thank you very much 
ĤΨ=EΨ
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spong
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The boiling should work, if not then hopefully you'll be able to get strong H2O2 at a hydroponics store, chemicals are hard to get in Australia too
(although probably not as bad as Croatia) but 50% H2O2 is available in black bottles called 'oxyplus' which is handy for heaps of things, especially
high powered elephants toothpaste
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KvantnaFizika
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I will surely need to see my hair dresser, she has the most powerful (i think 15%) peroxide in 100 km circle xD
Cheers for now, and thank you. I'll post results if I get any.
ĤΨ=EΨ
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spong
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Yeah 15% should work, the excess water can then be boiled off too. 50% is too strong to use anyway, I've heard piranha solution made with H2O2 above
50% could explode..
Good luck
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hissingnoise
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At its boiling point (337*C), sulphuric acid is a potent oxidiser!
Treatment with H2O2 is wholly unnecessary and wasteful!
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spong
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Oh yes the H2O2 is only if boiling alone doesn't work, hopefully it does though
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unionised
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That depends.
If you can get H2O2 easily but have difficulty getting the H2SO4 then using H2SO4 as an oxidant, and losing it as SO2 is a waste.
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MagicJigPipe
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| Quote: |
You could try heating the acid to its boiling point to oxidise the contaminant! Use a heavy pyrex casserole dish or similar and avoid inhaling the
fumes . . .
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I hate to undermine you like this, hissingnoise, but I must act:
DO NOT do this. Only use real lab glassware (borosilicate) for this. Some "Pyrex" baking dishes will be fine but others will not be and there is
almost no way to tell the difference. It's difficult to do a test under the same circumstances without the risk. If you are going to do this, at the
very least set the glass dish inside a larger metal pan filled with baking soda or something similar.
I did this once in my younger days and, as the H2SO4 was cooling down, the glass shattered and hot sulfuric acid spilled everywhere. Now THAT was a
hardcore cleanup.
I admit this was a "measuring bowl/cup" thing, but at the time I thought Pyrex meant Pyrex. It doesn't and I will never again trust Pyrex from
Wal-Mart or any other similar place.
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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hissingnoise
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| Quote: | | I admit this was a "measuring bowl/cup" thing, but at the time I thought Pyrex meant Pyrex. It doesn't and I will never again trust Pyrex from
Wal-Mart or any other similar place. |
I understand that in the US, tempered glass can carry the pyrex logo but pyrex was originally the name given to borosilicate glass for cooking.
If it's genuine pyrex, it won't shatter from thermal shock.
I trust my old, much abused glass saucepan for boiling H2SO4 more than I trust my quickfit glass, for some reason . . .
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watson.fawkes
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Quote: Originally posted by hissingnoise  |
I understand that in the US, tempered glass can carry the pyrex logo but pyrex was originally the name given to borosilicate glass for cooking.
If it's genuine pyrex, it won't shatter from thermal shock. |
Corning sold the use of the Pyrex brand
name a few years ago to a consumer products company for use in the US in the category household goods. They sell non-borosilicate ware under that
name. Corning, IMO, did some really stupid self-inflicted brand damage with this deal, but I'm not the trademark owner. Nevertheless, that soft glass
is also genuine Pyrex, because it's the trademark owner that gets to decide what's genuine. European housewares sold under the Pyrex name are still
borosilicate, to my knowledge.
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hissingnoise
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Actually, thinking back, I did (years ago) have "pyrex" measuring jugs shatter on me and I since figured that if it isn't intended for cooking on a
stove-top it's likely not genuine pyrex.
So the situation re the pyrex logo here probably mirrors that in the US.
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watson.fawkes
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| Quote: Originally posted by hissingnoise | Actually, thinking back, I did (years ago) have "pyrex" measuring jugs shatter on me and I since figured that if it isn't intended for cooking on a
stove-top it's likely not genuine pyrex.
So the situation re the pyrex logo here probably mirrors that in the US. |
You can break borosilicate with
thermal stress just like you can break soda-lime glass with thermal stress. The only difference is that with borosilicate it's a little harder. It's
certainly not impossible. You're in a race involving three physical parameters of glass, its thermal coefficient of expansion and its thermal
conductivity and its yield strength, and the temperature gradients at the surfaces of the glass. The thermal coefficient of borosilicate is lower than
soda-lime glass, but it's not zero. Put a thermal gradient onto the glass, it will conduct heat and settle into some differential expansion geometry,
complete with internal strain. Put a large enough thermal gradient on it, that internal strain will exceed its yield strength and you'll get cracks,
breaks, and general failure.
Putting glass straight onto a red-hot burner is risking breakage, period. Cooking vessels made of glass are generally tempered, which means they're
cooled in such a was as to lock in internal compressive strain on the surface (similar to pre-stressed concrete beams). They need to be tempered
because they fail if they're not, which means that glass for cooking vessels is operating at the edge of its engineering envelope.
My guess is that your measuring cup wasn't tempered, even though it may well have been made of borosilicate.
Aside: The CoE of quartz is very low, so that ware of ordinary sizes develops rather less internal strain than even borosilicate.
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Arthur Dent
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One trick I use to retrieve acid from my 2.5l jug of H2SO4 is to use a plastic graduated pipette, and on the top end, I just fit a pear-shaped rubber
bulb, like those used for solder removal, just take out the teflon tip. The result is a godzilla-sized eyedropper and there is no risk of spillage, or
dropping it at the bottom of the bottle. 
I've used that setup for years, it's a serological grade plastic pipette and when I'm done, I just wash it thoroughly in water. HNO3, H2SO4 and HCL do
not attack the plastic, but I wouldn't try this with glacial acetic acid though. I'll attach an image when i'm back home tonight.
As for your tainted acid, as mentioned above, even if purified, I wouldn't use it for critical experiments anymore, sadly.
Edit: Here's the pipette I described above: http://www.progmontreal.com/arch/pipette1.jpg
Robert
[Edited on 25-11-2010 by Arthur Dent]
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