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Name: Voigt
Status: educator
Age: 20s
Location: N/A
Country: N/A
Date: 4/26/2004


Question:
Hi, We are doing a science experiment and we were wondering what affect does extreme temperatures have on liquids such as alcohol, glycerine,cooking oil, and corn syrup. I believe that because of the fat content in the oils they will never freeze totally. Any insight on this matter would be great.


Replies:
I assume from the context that you are referring to temperatures colder than room temperature. As temperature is lowered most liquids crystallize. That is the "normal" behavior, but other things can happen. If the liquid is cooled rapidly its viscosity will increase so rapidly that the liquid molecules get "trapped" before they can migrate to a location in the crystal lattice of the solid. This "trapped" liquid state is called a glass. Some liquids for crystals some of the time, and glasses some of the time depending upon the detailed conditions. Of the liquids you mention -- glycerin, cooking oils, corn syrup -- will all likely form glasses because they are already rather viscous. Glycerin is a particularly interesting example because it melts at ~14 C., but almost nobody has ever seen crystalline glycerin because it forms a glass so readily. So the key to glass formation is the viscosity of the liquid at the freezing point and the cooling rate.

You might try another experiment too. Add some food colors to water and partially freeze the solution. You might see that the ice freezes clear and the dye stays in the liquid. This happens because ice has a rather complicated structure that excludes most molecules from the crystals when water begins to freeze. Good project.

Vince Calder


Dear Ms. Voight,

Thanks for your question. To the best of my knowledge, almost all substances will freeze if the temperature is lowered sufficiently (although the pressure may need to be raised). Even 4He, which condenses to a superfluid, will form a frozen solid if the pressure is raised by a few MPa (megaPascals).

Alcohol surely does freeze. Ordinary ethanol has a freezing point of -114 degrees Celsius; methanol freezes at a higher temperature (-97.7 deg. C). These temperatures cannot be achieved in a household refrigerator but are not difficult to achieve in the laboratory.

Cooking oil will also freeze if the temperature is lowered sufficiently. All fats will freeze. The CRC Handbook gives the following typical freezing points (individual oil samples can vary widely from these freezing points due to differences in composition):
SUBSTANCE     FREEZING POINT
corn oil              - 20 deg. C
sunflower oil         - 17 deg. C
olive oil             -  6 deg. C
sesame oil            -  6 deg. C
peanut oil               3 deg. C
palm oil                24.1 deg. C
coconut oil             25.1 deg. C

I hope this information is helpful.

best regards,

Dr. Topper



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