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Author: Subject: How do you clean stubbornly dirty glassware when no solvent seems to work?
Sidmadra
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[*] posted on 19-7-2018 at 20:01
How do you clean stubbornly dirty glassware when no solvent seems to work?


I've got a bunch of round bottom flasks from over the years that have been left unused because they have material in them that no solvent or hot alkali can seem to dissolve or get rid of. A few of the flasks are old rotovap flasks, and others are ones where very tarry reactions took place in.

If I could fit my hand in there I'm sure I could scrub the material away, but that's not an option. Abrasive cleaning powder is suggested by Sigma Aldrich but I have no idea how to actually use such.
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DraconicAcid
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[*] posted on 19-7-2018 at 20:05


I generally put in a bit of nitric acid and boil it with a Bunsen burner.



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Sidmadra
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[*] posted on 19-7-2018 at 20:13


Can you describe what a "bit" is? Concentration? And why a Bunsen burner in particular? When I think of Nitric Acid and open flames, potential boom come to mind.
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JJay
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[*] posted on 19-7-2018 at 20:17


Piranha solution will oxidize almost anything organic, including elemental carbon.



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XeonTheMGPony
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[*] posted on 19-7-2018 at 20:31


Quote: Originally posted by JJay  
Piranha solution will oxidize almost anything organic, including elemental carbon.


50ml 35% peroxide 150ml H2SO4 = dissolve any thing with carbon including carbon when heated.
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BromicAcid
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[*] posted on 20-7-2018 at 03:26


5% ammonium bifluoride solution and/or elbow grease.




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mackolol
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[*] posted on 20-7-2018 at 03:33


In most cases usual 98% sulphuric acid does the job. You can heat it if seems to not work. Also you can try with permanganic acid with h2so4 and kmno4 BUT USE CONCENTRATION OF H2SO4 LESS THAN 80% (if i remember well) AND DO IT CAREFULLY. Unless you will produce anhydride of permanganic acid Mn2O7 which will explode instantly in contact with any compound containing carbon.
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Sulaiman
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[*] posted on 20-7-2018 at 03:41


I have 6mm glass spheres that I use for column packing;

I 1/4-fill the vessel with glass beads then my solvent of choice (soap&water is good)
swirling this mixture cleans glass without any visible scratching.

I guess sand or salt or dirt would perform similarly.
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DavidJR
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[*] posted on 20-7-2018 at 03:53


Quote: Originally posted by mackolol  
Also you can try with permanganic acid with h2so4 and kmno4 BUT USE CONCENTRATION OF H2SO4 LESS THAN 80% (if i remember well) AND DO IT CAREFULLY. Unless you will produce anhydride of permanganic acid Mn2O7 which will explode instantly in contact with any compound containing carbon.


I would advise using 50% or less H2SO4 if you try this, because I had a bad experience with accidental manganese heptoxide even with care to stay below the touted 80%.




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CobaltChloride
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[*] posted on 20-7-2018 at 03:57


I have a bucket of Na3PO4 and strong detergent solution in which I soak my glassware. This seems to remove many stains and usually leaves the glassware sparkling clean. It was also able to loosen some waxy residue which was sticking to my RBF. After soaking I use a nylon tube brush from the supermarket which also has nylon fibers on its head to scrub the inside of the flask. If this doesn't work, I put some of that detergent+Na3PO4 solution in the flask and add some fine sand and swirl the flask so that the sand covers the interior. Sometimes I use sand and an organic solvent (like THF, acetone or naphtha). This way I was able to remove all stains.

[Edited on 20-7-2018 by CobaltChloride]
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DraconicAcid
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[*] posted on 20-7-2018 at 05:09


Quote: Originally posted by Sidmadra  
Can you describe what a "bit" is? Concentration? And why a Bunsen burner in particular? When I think of Nitric Acid and open flames, potential boom come to mind.


I pour in a few mL and boil that. Nitric acid is not flammable at all, so there's not going to be any potential boom unless it's mixed with an organic solvent that would go boom anyway.




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Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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[*] posted on 20-7-2018 at 05:20


There is a sticky on cleaning glassware. It contains a lot of good information and is well worth a read. If you cannot find a solution then there is definitely something very strange.
https://www.sciencemadness.org/whisper/viewthread.php?tid=24...

I will let this thread run as an active discussion rather than merge it. I think the sticky is quite concise without a lot of rambling discussion and it would be better to keep it that way. But I will put a link from there to here.
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DavidJR
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[*] posted on 20-7-2018 at 06:28


Has anyone tried a lab cleaning product called Decon 90? Tempted to order some and give it a go.

http://www.decon.co.uk/english/decon90.asp




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Sidmadra
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[*] posted on 20-7-2018 at 07:46


Thanks for all the replies everyone. I will try a number of these solutions and see what works best.



On a side note, does anyone know what the shelf stability/life is of Piranha solution?

[Edited on 20-7-2018 by Sidmadra]
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weilawei
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[*] posted on 20-7-2018 at 12:56


Don't store it. Make it, use it, neutralize it, and dispose of it in one session. See instructions on SM wiki.
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[*] posted on 21-7-2018 at 04:34


I like a base bath for stubborn stains. Just dump 4-8 ounces of NaOH per gallon of EtOH, let dissolve, soak dirty stuff overnight, and it will remove everything from glass, including some of the surface. We use that often for nasty goos and black tars.
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DavidJR
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[*] posted on 21-7-2018 at 15:38


Quote: Originally posted by Dr.Bob  
I like a base bath for stubborn stains. Just dump 4-8 ounces of NaOH per gallon of EtOH, let dissolve, soak dirty stuff overnight, and it will remove everything from glass, including some of the surface. We use that often for nasty goos and black tars.


Personally a base bath is routine cleaning for me. I don't call it stubborn until the base bath fails.

I use KOH in water though. It's just less hazardous than having vats of flammable liquids around. Also, I find KOH works better than NaOH because it's considerably easier to rinse off because of the increased solubility.




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[*] posted on 27-7-2018 at 16:34


Abrasive cleaning powder?

For cleaning diner coffee pots:Put Dutch Cleanser (Ajax etc.) in flask, add ice cubes.....Swirl.

If you need heat: Ajax, boiling water, and Glass Beads.... Might serve.
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[*] posted on 27-7-2018 at 16:57


Sodium thiosulfate for iodine, H2O2/H2SO4, ISPA, Nitric Acid, H2O2/HCl



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