graham@arcturus.uucp (Thomas D. Graham) (11/29/90)
Since I don't see a sci.chemistry group, thought this might be the next best palce for my question regarding methyl alcohol, methanol for short. Which is, is there any easy way to determine the amount of water mixed in with the methanol???? I have some methanol, but I suspect that it is contaminated with water. Could I simply take a small sample, say 2 oz, burn it and the remaining liquid is water?? Any ideas??? Thanks.
hbg6@citek.mcdphx.mot.com (12/03/90)
In article <1990Nov28.203618.7294@arcturus.uucp> graham@arcturus.uucp (Thomas D. Graham) writes: > > I have some methanol, but I suspect that it is > contaminated with water. Could I simply take a small sample, say 2 oz, > burn it and the remaining liquid is water?? Any ideas??? Thanks. If you put it in the freezer, wouldn't the water percipitate out as ice? (If you burned it, I would think the water would evaporate) John (not a chemist) Schuch
larry@kitty.UUCP (Larry Lippman) (12/03/90)
In article <14169@mcdphx.phx.mcd.mot.com>, hbg6@citek.mcdphx.mot.com writes: > > Since I don't see a sci.chemistry group, thought this might be the next > > best palce for my question regarding methyl alcohol, methanol for short. Sure, there's a chemistry group! - sci.chem > > Which is, is there any easy way to determine the amount of water mixed > > in with the methanol???? I have some methanol, but I suspect that it is > > contaminated with water. Could I simply take a small sample, say 2 oz, > > burn it and the remaining liquid is water?? Any ideas??? Thanks. Measure its specific gravity using a hydrometer, or measure its density using a specific gravity bottle or volumetric flask on an accurate balance. Calculation of the percent of water from the specific gravity is not difficult; an alternative is to find a table of methanol-water mixture constants in a chemistry or chemical engineering handbook. The above is probably the simplest method. While you could use freezing point depression or boiling point elevation, specific gravity is much more convenient. Probably the most common real world analytical laboratory method is more complicated, but is simpler to implement because it can be run on fully automated apparatus. It is called Karl Fischer titration. If *I* wanted to make this determination, I would put a sample in the Mettler KF titrator in my lab, and have an answer in a few minutes without any more than a few keystokes of data entry. > If you put it in the freezer, wouldn't the water percipitate out as ice? No, no, *NO*! Larry Lippman @ Recognition Research Corp. "Have you hugged your cat today?" VOICE: 716/688-1231 {boulder, rutgers, watmath}!ub!kitty!larry FAX: 716/741-9635 {utzoo, uunet}!/ \aerion!larry
mcdougal@tegra.COM (Steve McDougall) (12/04/90)
In article <1990Nov28.2618.7294@arcturus.uucp> graham@arcturus.uucp (Thomas D. Graham) writes: > > Which is, is there any easy way to determine the amount of water mixed > in with the methanol???? Well, it depends how much water you think there is and how exact an answer you need. Burning the mixture isn't a good idea, because if there is lots of water, it won't burn at all, and if there is only a little, it will evaporate when the methonal burns. If you only want to know if there is *any* water, you could look for something that reacts with water but not methaol. Maybe copper sulfate (Cu SO4). This is a white crystalline salt that turns blue in water. I don't know if it turns blue in methanol; I would guess not. If you want to know *how much* water you have, probably your best bet is to measure the density. For a quick and dirty check, just use a graduated cylinder and a scale to measure the volume and weight of a sample. The density of the sample will lie somewhere between the density of water and methonal. Given the density, you can compute the amount of water in the sample. However, the computation is *not* straightforward. The problem is that 1oz water mixed with 1oz methanol yields less than 2oz mixture, because the water and methaol molecules fit together in the mixture. A chemist or maybe CRC (Chemical Rubber Company Handbook) might be able to give you the approproate formula. The other problem with measuring density this way is that you can't measure volume very accurately with a graduated cylinder. I wouldn't count on an answer better than 5%, espically if there is only a little water. A better to measure the density of a liquid is with a flotation device. (I don't know what they are really called.) It has a thick weighted end that sinks into the liquid, and a thin hollow end that doesn't. The thin end has a scale along its length, and you read the scale where it intersects the surface of the liquid. The further into the liquid it sinks, the lower the density. These devices are used in places like the beverage industry. You might try a do-it-yourself wine making catalog or supply house. If you're lucky, you might find one that is calibrated directly in % methanol, although % ethanol is more likely (for obvious reasons). N.B. Places that use these flotation things often refer to density as "specific gravity".
henry@zoo.toronto.edu (Henry Spencer) (12/04/90)
In article <14169@mcdphx.phx.mcd.mot.com> hbg6@citek.mcdphx.mot.com writes: >If you put it in the freezer, wouldn't the water percipitate out as ice? No, or at least, not necessarily. The freezing behavior of such mixtures is complicated. Also, note that putting flammable fluids in your refrigerator is a really bad idea. The sealed space lets the vapor build up, and almost certainly the thermostat has open contacts that could supply an ignition spark... (Chemists use "explosion proof" refrigerators that have their thermostats and such very carefully sealed away.) -- "The average pointer, statistically, |Henry Spencer at U of Toronto Zoology points somewhere in X." -Hugh Redelmeier| henry@zoo.toronto.edu utzoo!henry