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Vogelzang
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Alcoholic beverage Russian roulette. If its methanol you go blind. If its ethanol you just get drunk. No, better not. You might not get your sight
back. How about a refractometer?
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marksev1
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There is another method, esterification of the alcohol with 3,5-dinitrobenzoic acid, and then measuring the melting temperature, if the sample would
be pure, the melting interval should be sharp, another way would be making a TLC analysis with this sample.
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kclo4
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| Quote: | | 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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uhh.. are you sure? I'd seriously double check that.
also... why wouldn't ethanol reduce copper as does methanol? I'm pretty sure it does...
[Edited on 23-8-2009 by kclo4]
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JohnWW
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What about doing an NMR analysis on it? CH3OH only has the alcoholic H on OH plus the three CH3 hydrogens, while ethanol also has a pair of -CH2-
hydrogens, which would be distinct.
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unionised
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Quote: Originally posted by JohnWW  | | What about doing an NMR analysis on it? CH3OH only has the alcoholic H on OH plus the three CH3 hydrogens, while ethanol also has a pair of -CH2-
hydrogens, which would be distinct. |
An elegant solution that only requires someone without so much as a heating mantle, to have access to an NMR spectrometer.
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not_important
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If one has a reasonable sensitive set of scales, the difference in solubility of NH4NO3 in the two alcohols could be exploited. Take say 50 cc of
each in two separate small flasks or bottles, and add sufficient NH4NO3 to each so that some of the nitrate remains undissolved. Let it sit overnight,
if all the nitrate dissolves add some more and let sit for a few more hours. The carefully pour off the clear liquid in order to get 25 cc, pour into
a tared beaker or small jar, allow to evaporate, and weigh. MeOH will dissolve 2 to 3 times as much NH4NO3 as EtOH in the 90% to 100% range. 100 g
100% MeOH dissolves 14.6 g NH4NO3 @ 14 C and 16.3 g @ 18,5 C and 17.1 g @ 20.5
Otherwise the methods for those not owning their own NMR, FTIR, mass spec, or even GC, would seem to be
1) boiling point, done in a test tube with the thermometer suspended in the vapour such that some condensate forms on the stem above the bulb.
2) iodoform test, MeOH will not give iodoform while ethanol and isopropanol will.
3) smelling, although many people can not distinguish the two alcohols.
4) density, although this does take a better set of scales and some care in measuring volumes given the small density differences.
5) giving some to a test animal, in amounts small enough that EtOH shouldn't kill it. Using one's neighbors or friends as the test animal may cause
inconvenience, as might larger pets especially from your own household. Stick to small rodents and don't talk about it to others.
6) Evaporation of a drop might do it, although when I tried this with 5 side by side comparisons only in one case was the MeOH clearly faster to
evaporate. Perhaps do the test on a bulky block of metal so that evaporative cooling doesn't slow down further evaporation of the drops.
Making the standard derivatives works, except that most people don't have the needed reagents at home. It's as easy to take the BP of the alcohol as
of an ester, so making an ester and measuring its BP is just extra work.
Oxidising a ml or two with hot acid dichromate and noting the odor might do, as both the corresponding aldehydes and carboxylic acids are fairly
distinct in their smells.
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marksev1
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Yes the boiling point would be suitable, but the "smell test", for sure one wouldn't distinguish if it was like 2% impurity of methanol in ethanol?
But nontheless maybe if you make the derivative and then have the bp of the liquid and also the bp of the derivative one can make a better quess of
the purity.
Concerning the TLC, here is the mobile phase, if someone is interested 8:10:1 cyclohexane:toluene:ethyl acetate.
Visualisation: spray with rhodamine B or UV 254nm.
Yes not very practical indeed.
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not_important
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Ah, but the thread started with two unlabeled bottles, one EtOH and one MeOh, both of lab grade. A side-by-side comparison should be able to
distinguish pre MeOH from EtOH with some MeOH denaturant - provide we're talking the oxidiser + smell test.
The possibilty of some MeOH in the EtOH reduces the value of some derivatives, as those of the two alcohols can be *%$%^ hard to separate or purify;
although TLC should do so. But you'd need kwon samples of the 2 alcohols to compare RF values of the unknow, and getting known samples of the
alcohols is what started this thread.
The boiling point could be done simply by banding two test tubes together and adding one of the unknown samples in each. Place in water bather a bit
below the BP of MeOH and fairly slowly raise the bath temperature. The MeOH will start boiling before the EtOH, even a few percent of MeOH in the
EtOH shouldn't be too hard to tell from pure MeOH. Raising the temperature above the BP of MeOH wil boil that tube dry while only reducing the volume
of the EtOIH to a slight extent.
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JohnWW
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| Quote: Originally posted by JohnWW | | What about doing an NMR analysis on it? CH3OH only has the alcoholic H on OH plus the three CH3 hydrogens, while ethanol also has a pair of -CH2-
hydrogens, which would be distinct. |
In addition, the IR spectrum of CH3OH should be distinct from that of
CH3CH2OH, as regards both "stretching" frequencies because ethanol has a C-C bond which methanol does not have, and "bending" frequencies because
ethanol has a C-C-O bending mode which methanol does not have.
See my upload of the Sigma-Aldrich IR and NMR spectral data and related materials in References, which would certainly include the spectra of both
alcohols.
[Edited on 25-8-09 by JohnWW]
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franklyn
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Methanol smells similar to acetone but not as floral and much less pungent.
Ethanol smells the same as any liquour.
Wet your pinky and with that your lips at the corner of your mouth. If it feels
and tastes much as liquour then its ethanol. If you feel a burning sensation
that lasts even after you wash , then its methanol.
Of course you must be certain that what you test is pure
and is not something else possibly carcinogenic.
.
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HydroCarbon
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I like this idea, simple and smart. Whichever one evaporates slower take a quick, short sniff to make sure it's ethanol.
Another idea might be to try and dissolve table salt in both. More salt should dissolve in methanol.
[Edited on 10-9-2009 by HydroCarbon]
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zed
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Hah! Simply take a little NaBH4, and dissolve it in your solvent. NaBH4 is fairly stable in Ethanol. Not so in Methanol. It will slowly decompose,
liberating bubbles of Hydrogen gas.
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bbartlog
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So far as evaporation tests go, might as well use your palm or the back of your hand. This mostly gets around the problem of evaporative cooling
bringing the evaporation times closer together, and on top of that the methanol should feel colder. In fact using a q-tip or the like to swab some on
(rather than just dripping a little drop) would probably give you a better feel for the difference in cooling.
If you're confident they're pure you could also look at the difference in conductivity. Both are effectively insulators, but ethanol has a higher
dielectric constant as I recall. Wouldn't take much in the way of dissolved salts to make that a useless measure though.
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