14 replies to this topic

[jollyhawley]

I'm a science teacher buying supplies for this year and was wondering how much of a difference 95% ethanol would be from pure. I am planning on primarily using it for flame tests. I am also going to use it as a substitute for liquid nitrogen by putting it in a beaker with dry ice. I suppose it might not be quite as cold as pure ethanol, but that's the only drawback I can think of. I almost feel silly posting a question like this, but I thought it wouldn't hurt to ask- maybe I'd get some insight. If any of you have any suggestions on where to buy ethanol, that would be great too. The best price I've found so far is at carolina.com. Thanks.

[Comandante]

I buy 98% ethanol quite cheaply from hardware store, not even brand chem suppliers. Works great as burning fuel so you can probably use it for flame tests, it also feels very cold when poured over hand so I guess you may use it to some extent with dry ice, not sure though what exactly you have in mind. For most organic reactions however, it's doomed to fail - not that I myself have tried but from what I heard others report.

[Melvin]

I believe that any ethanol concentration above 40% will burn, so 95% is great for burning. (96% is actually the max that can be created by normal distillation). And it still should have a low enough melting point to be used with dry ice.

[hermanntrude]

there are very few situations where you'll need absolute ethanol

[UC]

I'm a science teacher buying supplies for this year and was wondering how much of a difference 95% ethanol would be from pure. I am planning on primarily using it for flame tests. I am also going to use it as a substitute for liquid nitrogen by putting it in a beaker with dry ice. I suppose it might not be quite as cold as pure ethanol, but that's the only drawback I can think of. I almost feel silly posting a question like this, but I thought it wouldn't hurt to ask- maybe I'd get some insight. If any of you have any suggestions on where to buy ethanol, that would be great too. The best price I've found so far is at carolina.com. Thanks.

Use dry ice in acetone. It works quite well and is cheap. You may freeze out water from the azeotropic 95% by adding dry ice.

Methanol is much better for flame tests as the flame is a consistent clear blue.

[jdurg]

I will just re-state the obvious here, but the difference between liter of 100% ethanol and 95% ethanol is 50 mL of H2O. Ethanol is also the alcohol of intoxication, so when you purchase concentrated ethanol it typically contains a small amount of methanol and some various other compounds to make the drinking of it impossible. (Concentrated ethanol suitable for drinking is subject to MANY taxes. The type that is commonly bought for chemistry labs is denatured, yet suitable for whatever it would be used for).

If you just want something that burns and is also able to be used to make cold solutions, I agree with the acetone suggestion. Acetone is VERY cheap, VERY flammable, and when mixed with dry ice creates a solution that is incredibly cold.

[jollyhawley]

Thanks for the suggestions... I hadn't thought about using acetone with the dry ice- good to know!
I thought about using methanol for the flame tests as I've heard that it is better suited for that. However, I've also heard that it's very dangerous to burn methanol because the flame is clear. That scared me away from it- I don't want a liability on my hands. What has your experience with it been?

[CaptainPanic]

100% ethanol will burn at higher temperature than 95% (wt, vol?).

Also a comment: To all those who posted here, please write what kind of percentage you mean. There exist several options: weight%, volume%, molar%. These are not the same thing.

Normally, in the ethanol industry, volume% are used. But you MUST write "%vol"...

[John Cuthber]

Crassly off topic but...
Acetone eats the polystyrene that is often used to make cheap insulated containers for very cold things like dry ice.

You may also wish to note that methanol is rather more toxic than ethanol. In practical terms this doesn't matter (nobody is drinking it) but someone might ask if you have done your best to replace chemicals with less toxic ones where reasonably practical. (It's a legal requrement to do so in the UK).
And, (back to the topic agian before the Mods get upset)
For flame tests the few % of water won't matter. (and for captain P's benefit, that's a few mole %)

[raid517]

So can pure ethanol be bought legally in the UK or not and if so where? I have some Polish recipes for preserving food and fruit (which is my main area of interest) and these require ethanol of the highest possible purity. (So no dangerous additives to make it unfit for human consumption).

Edited by raid517, 8 October 2009 - 01:36 PM.

[insane_alien]

no, you can't buy pure ethanol without a license.

[John Cuthber]

You can buy alcoholic drinks with up to about 80% ABV without much difficulty (as long as you are over 18 of course)

[hermanntrude]

I'd imagine that the recipes originally would have used very strong vodka rather than pure alcohol. It's very hard to make pure alcohol, even when it isn't illegal.

[raid517]

I think a lot of poles had their own distilleries for this and did make very high grade alcohol. There is quite a tradition of preserving food this way in Poland. Alcohol that is especially pure 95% + is said to be especially good at preserving the flavours of certain types of food (particularly fruits).

Anyway what better way to enjoy one's s-self at a social gathering than to present them with a bowl of fruit that has been preserved in alcohol. Fruit that gets you drunk... It's a pity nature didn't think of it first.... ;-)

Edited by raid517, 8 October 2009 - 08:17 PM.

[Mr Skeptic]

The main problem with the 95% ethanol you can buy in stores is usually not the 5% water, it is the few percent of additives which are added precisely to make them unfit for human consumption.