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Agent MadHatter
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How do you tell methanol from ethanol?
I have two bottles of solvents. One is ethanol, one is methanol. I got them from my lab today, and they were in the correct placement.
Sadly they got mixed up, and now I can't figure out which one is which. I need to mark them before next time...
How do you tell one from the other? I tried smelling, but I couldn't tell. One was alittle stronger, but I don't want to risk it.
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Agent MadHatter
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Oh, and I don't have any chemicals like potassium to test it with.
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497
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Boiling point...
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Agent MadHatter
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I don't have a heating mantle. I forgot to mention that. I rather not use an open flame.
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497
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Ever heard of a boiling water bath? Also, you only need to boil a small amount, so I wouldn't worry about open flames.
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Agent MadHatter
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I found it out. Thank you.
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Sedit
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Care to share what you found out with the rest of us?
edit:spelling
[Edited on 4-8-2009 by Sedit]
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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bfesser
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A drop of each on the bench. MeOH should evaporate faster.
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kclo4
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How did you determine it?
I was going to suggest forming an ester with one that would have a distinctive smell, BP, MP, etc compared to the other, or making the corresponding
ether. Dimethyl ether, isn't nearly as easy to condense as Diethyl either.
Oxidation could be an option as well since formaldehyde, an intermediate in the oxidation of ethanol, smells of apples, while formaldehyde does not.
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bfesser
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Be sure to always label your chemicals carefully to avoid such confusion in the future--and to avoid ending up like Mr. Deeb! I find that a strip of
clear packing tape helps prevent wear and spills on them.
[Edited on 8/4/09 by bfesser]
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kclo4
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Who is, and what happened to Mr. Deebs?
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bfesser
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I don't mean to take this thread off topic, but since it's going nowhere fast anyways...
http://pubs.acs.org/cen/science/86/8645sci1.html
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not_important
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Boiling point is simple, slightly more complex is the iodoform reaction http://www.chemguide.co.uk/organicprops/alcohols/iodoform.ht...
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gsd
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Heat on flame a copper wire till red hot.
Extinguish the flame.
Open bottle of alcohol.
Take small quantity in a beaker.
Dip the copper wire quickly into it.
If it is methanol, you will get distinct pungent smell of formaldehyde.
gsd
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woelen
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Smell both of them carefully. Ethanol has a much stronger smell than methanol. Do not smell too long and too mucht, because methanol is quite toxic. A
few whiffs of the vapor won't harm you, but do not smell many times and do not deeply breathe the vapors.
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watson.fawkes
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Quote: Originally posted by woelen  | | Smell both of them carefully. Ethanol has a much stronger smell than methanol. Do not smell too long and too mucht, because methanol is quite toxic. A
few whiffs of the vapor won't harm you, but do not smell many times and do not deeply breathe the vapors. |
Incidentally, the medical treatment for methanol poisoning is ingestion of ethanol. As I recall, methanol and ethanol share a
primary catabolic pathway. When methanol goes through, it's toxic; when ethanol goes through, it's not. Ethanol, though, has a greater affinity for
the pathway. When sufficient ethanol is present, methanol is excluded from the primary pathway and goes to a secondary one, which does not create
toxicity. This is why certain traditional liqueurs, such as kirsch, have non-trivial amounts of methanol (it's part of their flavor, in fact) but
aren't toxic, because, as it were, you drink the poison together with its cure.
So after your smell test, imbibe a distilled beverage of your choice. No harm done.
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JohnWW
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That is correct. Methanol, in the absence of anything else, is metabolized by liver enzymes to formaldehyde and then formic acid, which attacks the
entire nervous system, especially the optic nerves. Ethanol is preferentially (to methanol) metabolized to acetic acid, much less toxic, via
acetaldehyde. Isopropanol, if ingested, is converted to acetone, but no further as this is a ketone, not an oxidizable aldehyde, being thus much less
acid in its effects.
[Edited on 5-8-09 by JohnWW]
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Rich_Insane
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Both methanol and ethanol are metabolized by the alcohol dehydrogenase pathway. Ethanol is converted into an aldehyde (acetalhyde I believe, then
CH3COOH) while methanol becomes formic acid and formaldehyde. So ethanol is an allosteric inhibitor, where it competes and "steals" the enzyme from
methanol while methanol is excreted. But I do not advise anyone to chug a bottle of methanol.
As for testing between the two, I believe just dropping a drop on a hard surface will tell. However, I know distinctly that methanol has a slightly
different smell than ethanol. Somehow ethanol seems stronger to me. Of course this is 95%, non-methylated EtOH in the lab I work in.
I really would do BP, because it is quite simple. Just heat one sample gently.
As an alternative you could find a really cold freezer and do MP, but I highly doubt that's something you want to do.
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UnintentionalChaos
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I'd just go with the iodoform reaction. add a tiny spatula of KI or NaI to a test tube with a few drops of the alcohol, then a dropper of bleach.
Results should be immediate and telling.
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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Formatik
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| Quote: Originally posted by woelen | | Smell both of them carefully. Ethanol has a much stronger smell than methanol. Do not smell too long and too mucht, because methanol is quite toxic. A
few whiffs of the vapor won't harm you, but do not smell many times and do not deeply breathe the vapors. |
Don't even breathe low amounts methanol vapors on a long-term basis either, since this promotes blindness and vision problems:
The most common health effect of long-term exposure to low levels of methanol vapor is CNS and ocular effects.
http://toxsci.oxfordjournals.org/cgi/content/full/88/1/30
[Edited on 5-8-2009 by Formatik]
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BromicAcid
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A good scale and a good volumetric flask would allow for a density measurement. Problem is that they differ by only a few thousandths of a gram per
liter so if you have one of those cheap postage scales it just won't cut it.
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Jor
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The best is the iodoform test, as indicated by UnintentionalChaos. Smelling is also possible. Methanol isn't that toxic, it has a PEL of 200ppm
average 8-hour, wich is very high for a 'toxic' chemical. I wonder why it has the 'toxic' symbol as the lowest published oral fatal dose for a human
is 428mg/kg, and the LD50 for mouse is much higher. This means that is should be Xn: Harmful.
Is it just that they call it toxic because it is has killed so many people?
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woelen
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Oh yes, the history of (ab)use of a chemical has the same (or even more) influence on the classification of a chemical as its actual toxicity.
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marksev1
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A bit of topic, how to identify if you have present methanol in ethanol and maybe to also quantify these presence... or there some identification
reagents, i hope not so exotic and hard to reach... I can only think about a GC analysis but that is out of reach for most hobby chemists.
[Edited on 6-8-2009 by marksev1]
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a_bab
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The method with the copper wire is a good one (methanol reduces the copper oxides, leaving the copper nice and red).
But here is a better, more beautiful one: boric acid. Methanol burns green with a bit of boric acid mixed in it, while ethanol does not.
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