FrickinA
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Purification of Potassium Hydroxide
I have recently acquired 2 lb of technical grade KOH, now, i dont have any use in mind right now, but I know it is often useful in various syntheses
and so I jumped at the opportunity to get it. Unfortunately its only 90% pure. Im assuming the impurities are soluble, otherwise it wouldve been
filtered (this stuff is listed as tech. grade KOH for soap and biodiesel, it is not a product that uses KOH as a main ingredient).
Anyone have any idea how I might purify this at all? I can get a list of the analysis results if it would help
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madscientist
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Any details on what the impurities might be would help. Hard to know what to suggest otherwise.
I weep at the sight of flaming acetic anhydride.
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Magic Muzzlet
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85/90% KOH is regarded as reasonably pure I believe, the impurities being water and potassium carbonate that cannot be removed. I'd say trying to
purify it would result in more contamination. What you have should be fine for all uses. Unless of course it has dyes or something like that on it.
Just looked at the product, and man, that looks great. Doesnt seem like a thing needs to be done to me. 
[Edited on 29-10-2010 by Magic Muzzlet]
[Edited on 29-10-2010 by Magic Muzzlet]
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FrickinA
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This is the product I have.
http://www.essentialdepot.com/msds/KOH_COA.jpg
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bbartlog
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The assay doesn't show much carbonate... further unless it were manufactured by 19th century processes (from ashes) or unnecessarily exposed to air I
wouldn't expect 10% K2CO3. Maybe KCl, assuming it was made via electrolysis of same. NaOH I suppose is also possible but IMO less likely. I would just
account for the impurity when doing the stoichiometry and not worry about it unless there really seems to be a problem. I suppose if the contaminant
is KCl you could dissolve your product in cold 95+% ethanol (which should leave all or almost all the KCl behind), filter, and then evaporate off the
ethanol to leave behind purified KOH. But like madscientist says, you really want to know what the contaminant is to decide on an approach.
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mr.crow
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It says its food grade and looks pretty damn pure
To make KOH they MELT it and drip it on to a conveyor belt to form beads. Even that isn't enough to get rid of the water, that's how hygroscopic it
is. Exposure to air makes a layer of carbonate too. ACS grade is labeled as 85%+, the rest being water.
Double, double toil and trouble; Fire burn, and caldron bubble
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FrickinA
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Alright well I'll assume that for anything I use it for I just have to worry about the stoichiometry and not side reactions. Thanks for the replies
guys.
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