MadSci Network: Chemistry
Query:

Re: Is it possible to lower the boiling point of water by adding a substance?

Date: Thu Sep 2 09:22:44 1999
Posted By: Dan Berger, Faculty Chemistry/Science, Bluffton College
Area of science: Chemistry
ID: 936111083.Ch
Message:

Is it possible to lower the boiling point of water by adding a substance?

What (if any) substance can be added to pure water to significantly decrease the boiling point of the solution? I know that a mixture of 95.6% ethanol and 4.4% water has a constant B.P. of 78.2 degC. But can a chemical be added to water and achieve a similar effect? The simil ar question in your archives never actually names a substance.


The answer linked above is the one I found with the same topic heading. The phenomenon to which you refer is that of forming an azeotrope, a mixture of two liquids which cannot be separated by distillation because the mixture has a lower boiling point than either of the pure liquids. Azeotroping is why you cannot isolate ethanol by distillation without using a drying agent, something that preferentially soaks up water. But in the ethanol/water azeotrope, ethanol is the major component. And when you distill a mixture of ethanol and water which is less than 95% ethanol, you leave pure water behind.

It sounds like what you are after is an azeotrope of some substance with water, in which water is the major component. The way to find one is to consult a table of azeotropes, such as the one in the Handbook of Chemistry and Physics. Any reasonably-stocked public library, and any college library at all, should have a copy.

If you can't find a copy of the Handbook, drop me an E-mail and I'll see what I can do. Good luck!

  Dan Berger
  Bluffton College
  http://cs.bluffton.edu/~berger


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