In my O-Chem experiment, I had to extract and isolate caffeine from tea, and then purify it, and take the melting point. The mp of pure caffeine supposed to be 237C, while mine (and others, and according to the text it should be this way) was lower: 219C. WHY? it's one of the question for the post-lab. HELP!
2006-10-08 12:38:31 · 5 answers · asked by Thi 2 in Science & Mathematics ➔ Chemistry
The purification was done by sublimation (solid->gas, then solid on "cold finger"(ice-cold water test tube)) so it's supposed to be pure. The mp was maybe 218-219. Maybe some impurities were sublimed as well, it was not supposed to though.
2006-10-08 13:00:42 · update #1
Your melting point is depressed due to impurities in your sample. Your caffeine is not 100% pure, not knowing your isolation procedure, my guess is you impurity is likely solvent.
BTW- Melting points should always be reported as a range. For example Aldrich lists two ranges for caffeine's melting point. 234-236.5C and 235-237C.
http://www.sigmaaldrich.com/catalog/search/ProductDetail/FLUKA/84677
2006-10-08 12:55:51 · answer #1 · answered by Chris M 2 · 2⤊ 0⤋
Melting Point Of Caffeine
2016-12-18 06:14:01 · answer #2 · answered by woolf 4 · 0⤊ 0⤋
Caffeine Melting Point
2016-10-01 03:25:44 · answer #3 · answered by ? 4 · 0⤊ 0⤋
There are impurities in your sample. What did you use as a drying agent? If you used excess drying agent, that would cause impurities in your sample. Also, regular caffeine is very difficult to get a melting point of---it is subliminal, meaning it skips the liquid phase! Are you sure you didn't take the melting point of caffeine salicylate, the derivative of caffeine?
2013-11-12 03:25:38 · answer #4 · answered by ? 1 · 0⤊ 0⤋
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Melting point caffeine?
In my O-Chem experiment, I had to extract and isolate caffeine from tea, and then purify it, and take the melting point. The mp of pure caffeine supposed to be 237C, while mine (and others, and according to the text it should be this way) was lower: 219C. WHY? it's one of the question for the...
2015-08-05 22:05:20 · answer #5 · answered by Anonymous · 0⤊ 0⤋
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it all depends upon the sophisitcation of the lab. do you have melting point lab equipment? capillary tubes, circulating oil bath to place the capillary tube in, hot enough flame for you to reach 238C (460ºF)? did you get the caffeine from a purification process or was it given to you as a powder? if you purified it yourself, then there most likely would be impurities that could increase the bp higher than the 460ºF required to melt the caffeine. there could be a number of safety reasons
2016-03-27 00:36:04 · answer #6 · answered by ? 4 · 0⤊ 0⤋
Maybe your purification process wasn't perfect, and there were impurities in your caffiene that were affecting the melting point?
219C and 237C isn't THAT different?
Or maybe your themometer was lying?
2006-10-08 12:40:51 · answer #7 · answered by PJ 3 · 0⤊ 0⤋