Twospoons
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NaOH in EtOH, colour?
This morning I made some etch solution for polyimide (Kapton), cosisting of 6% wt NaOH in 80% wt EtOH / 20% wt H2O. Initially the solution was
clear, but turned piss yellow over 45 minutes as I drove in to work. The etch solution still worked, but not as well as I would have expected. Is
this colour change normal, or have I got some contaminant in there? The ethanol was distilled (twice) from a yeast ferment, and filtered with
activated carbon.
Can anyone tell me what happend?
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runlabrun
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it might be contamination from the container.. either from improper cleaning or the solution may have taken something from the material?
The reagent mixture should not have any colour, so the origin of your colour must be from some form of contamination.
-rlr
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Polverone
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Solutions of NaOH or KOH in ethanol, even using pure materials in clean containers, discolor on exposure to air. I have heard that this is due to the
oxidation of the ethanol by atmospheric oxygen under strongly alkaline conditions, creating acetaldehyde which condenses to form colored products.
PGP Key and corresponding e-mail address
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Pyridinium
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| Quote: | Originally posted by Polverone
Solutions of NaOH or KOH in ethanol, even using pure materials in clean containers, discolor on exposure to air. I have heard that this is due to the
oxidation of the ethanol by atmospheric oxygen under strongly alkaline conditions, creating acetaldehyde which condenses to form colored products.
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I've seen EtOH/KOH solutions discolor as well. Dull yellowish. The odor changes, becomes mildly unpleasant, but it's barely detectable
above the baseline alcohol odor. It happens faster with denatured ethanol.
You can get some pretty interesting products in small amounts, I'm sure. I don't have a mass spec rig handy to find out what they are, but
I'd love to know if anyone here has familiarity w/ them.
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Pyridinium
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update
I cleaned some droppers in that vaguely unpleasant-smelling denat.EtOH/KOH solution. One of the droppers had traces of Fe(OH)3 and I think MnO2...
not sure if this caused the change, but:
I noticed the alcohol went from smelling disagreeable to having an almost pleasant odor, like honey mustard and onion pretzels.
I really would like to know what's in it now.
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