[mattusha]

Hi,

I recently did an experiment in organic chemistry where we extracted caffeine from coffee by adding dichloromethane to a coffee sample and heating at reflux for solid-liquid extraction. We then did gravity filtration (not hot), and during this step I noticed that small white crystals formed on the edges of the filter paper. My lab instructed assured me that these crystals were water crystals, and when I asked him why they formed on the fringe of the filter paper, he merely smiled and told me to think about it. I have been thinking about it, and thought it might be because dichloromethane and water are immiscible, so the water creeps up the edges of the filter paper and crystallizes (a weak theory, I know). I also thought it might be water sublimation, but again, I have my doubts. I was hoping someone here might be able to help me figure out why these water crystals are forming, as it is really bothering me. Any help is appreciated. Thanks.

[Arkcon]

Crystalline water has another name -- ice.  At standard pressures, its not stable at temperatures above 0 °C.  Either your lab is very cold, or there is another explanation.

[orgopete]

Either your lab is very cold, or there is another explanation.

Hint, does it take energy to cause evaporation (does your body sweat to keep you cool)?

[Borek]

Nice! I know something similar can be done with diethyl ether.