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Author: Subject: Removing KMnO4 stains
egloskerry
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[*] posted on 14-4-2007 at 16:40
Removing KMnO4 stains


As anyone who has worked with KMnO4 knows, it causes brown stains that are impossible to remove from surfaces or skin without a harsh abrasive. I remember reading somewhere that sodium bisulfate will remove the stains. Is this true? Does anyone know of anything that will remove them? I've tried 3% H2O2, 91% isopropyl, ethanol, and gojo. Nothing works on my hands or the floor.

[Edited on 14-4-2007 by egloskerry]
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Ozone
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[*] posted on 14-4-2007 at 16:48


Hello,

The brown stuff is manganese dioxide, MnO2.

Please check out the search function for things like:
http://www.sciencemadness.org/talk/viewthread.php?tid=7375&a...

Since it is not mentioned there, I will say that oxidative treatment, save HNO3 (conc.), will get you no where. Reductive agents such as sodium metabisulfite or hydroxylamine will get the job done (under mild conditions, instantly).

Cheers,

O3




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egloskerry
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[*] posted on 14-4-2007 at 16:56


So I bought this bisulfate for nothing? I must've been thinking of bisulfite.

[Edited on 14-4-2007 by egloskerry]
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joeflsts
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[*] posted on 14-4-2007 at 17:46


Quote:
Originally posted by egloskerry
So I bought this bisulfate for nothing? I must've been thinking of bisulfite.

[Edited on 14-4-2007 by egloskerry]


Depends. If you are into Halogens and experimenting with Chlorine - the bisulfate is one way there.

Joe
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[*] posted on 14-4-2007 at 19:49


But for removing the MnO2, you want bisulfite. In fact, metabisulfite is normally the preferred version of this (cheaper, purer, more stable). It is cheap. I can find it at the local brewing supply store.
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[*] posted on 15-4-2007 at 04:21


Lemon juice works too. It smells better than bisulphite and it's easy to get hold of.
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[*] posted on 15-4-2007 at 08:42


Ascorbic acid works too, and is probably the most skin-friendly.

[Edited on 15-4-2007 by garage chemist]




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[*] posted on 15-4-2007 at 10:21


I'm pretty sure oxalic acid works as well (unfortunately, not as skin friendly as ascorbic)
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[*] posted on 15-4-2007 at 17:43


Orange juice works. Any acid that is reducing.
Or use Hydrogen peroxide mixed with vinegar (works fastest).
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[*] posted on 16-4-2007 at 01:36


I have best experience with a solution of sodium (bi)sulfite in dilute HCl (3% or so). Such a solution is not really corrosive and does not involve toxic stuff. Of course you should not let it act upon skin for a long time, but the few seconds of exposure, needed for cleaning up are not a problem at all.
This solution also is great for cleaning KMnO4-stains from glassware, ceramics and also from tables, workbenches etc. Do not apply it to clothes/fabric, because of its bleaching action.




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dedalus
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[*] posted on 16-4-2007 at 08:31


I always use HCl. You need good ventilation because chlorine is released.
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[*] posted on 16-4-2007 at 10:18


Hmm?
"I have best experience with a solution of sodium (bi)sulfite in dilute HCl (3% or so). Such a solution is not really corrosive and does not involve toxic stuff. "
OK, you put that in your gin and tonnic and I will put lemmon in mine.....
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[*] posted on 16-4-2007 at 13:57


Do you really think HCl 3% and sulfite are toxic? Of course you should not eat or drink them, but for the rest these are rather benign. Also because of the low concentration of the acid and the small amount of sulfite needed, the level of SO2-formation also is very low. You can smell it, but it's not irritating. The reason I like this mix is its instant action on permanganate and MnO2 stains, and it also can be applied on skin.

My other favorite stain remover is a warm mix of concentrated H2SO4 and solid NaF. It also works really good in removing KMnO4 stains, making a beautiful green solution of MnO3F. However, this solution is somewhat more toxic than 3% HCl + a pinch of sulfite :D.

[Edited on 16-4-07 by woelen]




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[*] posted on 17-4-2007 at 06:35


It depends a lot on how sensitive you are to SO2. I once worked with a guy who'd break out in hives from sodium metabisulfite. And, some asthmatics are liable to have an attack triggered by them. Sulfuites, I mean.

I just don't like the smell.
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egloskerry
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[*] posted on 11-5-2007 at 11:40


Well, I had a large stain, and tried a highly concentrated solution of sodium bisulfate heated to boiling with a propane torch. Worked pretty well.
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[*] posted on 11-5-2007 at 11:48


Quote:
Originally posted by woelen
My other favorite stain remover is a warm mix of concentrated H2SO4 and solid NaF.
[Edited on 16-4-07 by woelen]


True, I suppose when you're dead, stains are no longer a major concern :P

Never tried the MnO3F formation. It does sound interesting. I'm fascinated with complex ions.
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[*] posted on 12-5-2007 at 13:22


Well, I actually did the experiment. I still need to update the webpage, where I say this is probably MnO3F. I have a newer text book, which confirms the formation of MnO3F.

http://woelen.scheikunde.net/science/chem/exps/KMnO4+NaF+H2S...




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[*] posted on 27-5-2007 at 14:17


For skin, if newly stained, 3% H2O2 - or a light scouring pad will do it. Stain is surface only, due to (probably) unsaturated skin oils.

DerAlte
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