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.DraconicAcid - 19-7-2018 at 20:05
I generally put in a bit of nitric acid and boil it with a Bunsen burner.Sidmadra - 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.JJay - 19-7-2018 at 20:17
Piranha solution will oxidize almost anything organic, including elemental carbon.XeonTheMGPony - 19-7-2018 at 20:31
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. Sulaiman - 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.DavidJR - 20-7-2018 at 03:53
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%. CobaltChloride - 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]DraconicAcid - 20-7-2018 at 05:09
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.j_sum1 - 20-7-2018 at 05:20
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.DavidJR - 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.
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]weilawei - 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.Dr.Bob - 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. DavidJR - 21-7-2018 at 15:38
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.zed - 27-7-2018 at 16:34
Abrasive cleaning powder?
For cleaning diner coffee potsut Dutch Cleanser (Ajax etc.) in flask, add ice
cubes.....Swirl.
If you need heat: Ajax, boiling water, and Glass Beads.... Might serve. VSEPR_VOID - 27-7-2018 at 16:57
Sodium thiosulfate for iodine, H2O2/H2SO4, ISPA, Nitric Acid, H2O2/HCl
ut Dutch Cleanser (Ajax etc.) in flask, add ice
cubes.....Swirl.