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.Agent MadHatter - 3-8-2009 at 16:23
Oh, and I don't have any chemicals like potassium to test it with.497 - 3-8-2009 at 16:30
Boiling point... Agent MadHatter - 3-8-2009 at 16:33
I don't have a heating mantle. I forgot to mention that. I rather not use an open flame.497 - 3-8-2009 at 16:37
Ever heard of a boiling water bath? Also, you only need to boil a small amount, so I wouldn't worry about open flames.Agent MadHatter - 3-8-2009 at 16:53
I found it out. Thank you.Sedit - 3-8-2009 at 17:08
Care to share what you found out with the rest of us?
edit:spelling
[Edited on 4-8-2009 by Sedit]bfesser - 3-8-2009 at 18:18
A drop of each on the bench. MeOH should evaporate faster.kclo4 - 3-8-2009 at 18:18
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. bfesser - 3-8-2009 at 18:23
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]kclo4 - 3-8-2009 at 18:29
Who is, and what happened to Mr. Deebs? bfesser - 3-8-2009 at 18:38
I don't mean to take this thread off topic, but since it's going nowhere fast anyways...
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 woelen - 4-8-2009 at 11:13
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.watson.fawkes - 4-8-2009 at 13:40
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.JohnWW - 4-8-2009 at 16:42
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]Rich_Insane - 5-8-2009 at 08:57
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.UnintentionalChaos - 5-8-2009 at 09:03
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.Formatik - 5-8-2009 at 11:17
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:
[Edited on 5-8-2009 by Formatik]BromicAcid - 5-8-2009 at 15:29
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.Jor - 5-8-2009 at 15:36
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?woelen - 5-8-2009 at 22:47
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.marksev1 - 6-8-2009 at 03:42
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]a_bab - 10-8-2009 at 12:13
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.Vogelzang - 22-8-2009 at 15:01
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?marksev1 - 23-8-2009 at 00:58
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.kclo4 - 23-8-2009 at 01:43
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.
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]JohnWW - 23-8-2009 at 01:51
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.unionised - 23-8-2009 at 05:10
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.not_important - 23-8-2009 at 07:21
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.
marksev1 - 23-8-2009 at 12:03
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. not_important - 23-8-2009 at 20:57
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.
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]franklyn - 2-9-2009 at 14:58
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.
A drop of each on the bench. MeOH should evaporate faster.
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]zed - 9-9-2009 at 20:53
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. bbartlog - 10-9-2009 at 10:32
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.
