How fast does 99.5% ethanol lose concentration? - (Dec/10/2007 )
I have a bottle labeled 99.5% Ethanol, which is all nice and fine, but then I have this nagging feeling that as soon as I open the bottle, humidity from the air will dissolve in the hyper-dry Ethanol and lower the concentration.
What I wonder is - how fast does this happen (will my bottle drop down to 96% the first time I open it, or will it be 99.2% after having had it opened on my bench for a whole day?) and about what concentration will it settle at (I suppose it depends on the local humidity, but there should be some kind of guideline, I think one of my advisers said 95% at some point).
Another one of those little details...
Probably this is an over reaction. Water vapor has to go through a thick layer of ethanol vapor to reach the liquid below, a loose cap wont be that a problem so severe. How anhydrous do you need for your experiment?
You're right, relative humidity will play a part in this as well as factors such as, the open surface area of ethanol exposed to the atmosphere and temperature of ethanol.
Ethanol is hygroscopic but as long as you decant from your stock bottle and keep your stock bottle tightly closed I would never imagine you'd have a problem.
You never put working solution back into your stock, right?
Where the ethanol:water reaches equilibrium I have no idea. We need some proper chemists in here to answer that.
Really? That's stored in the memory bank. Cheers, mdfenko.
This much moisture get into a bottle that has positive pressure due to ethanol vapor???
over a period of time, yes.
Thanks a lot for the help. Then I can be fairly confident that my stock bottle will keep its concentration. I'm not really that much in need of pure EtOH right now, but when I dilute from the bottle I wold like to know what my starting concentration is.
I hate to be the English pedant and correct other's mistakes (I make more than enough of my own), but in this case I will be, both because I see the error so often, and because we have an international group, some of whom are learning and planning on writing in English. The word you are looking for in the title is lose, not loose. Loose means not tight. Lose means to not find. Thank you for your attention. http://www.wsu.edu:8001/~brians/errors/lose.html
Oooops! Thanks for pointing out the mistake. I've changed it.