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Name: JD
Status: student
Grade: 9-12
Location: FL
Country: New Zealand
Date: Winter 2011-2012

Question:
Do soluble substances evaporate with the water?

Replies:
JD,

As a general rule, no. If the soluble substance is a solid, then its boiling point is well above that of water, so it cannot possibly boil off. If the substance is a liquid, it may have a boiling point that is below that of water and will boil off at a lower temperature than water. If the boiling point is higher than that of water, than it will boil off after the water has evaporated.

Some substances, like ethanol for example, form an "azeotrope" with water. The combination of ethanol and water form a tight intermolecular connection that makes the two substances boil off at the same time.

There is also an issue of "entrainment". If you boil something vigorously, the strong bubbling causes the otherwise separate substance to be included in the boiling water. If you boil salt water hard enough, the bubbling and roiling of the water can cause the salt to climb along the walls of the container. This is not technically a boiling of the salt, the salt is just being carried by the strong evaporation rate.

Greg (Roberto Gregorius) Canisius College


Some do and some do not. It is dependent on how volatile they are. Alcohols will, for example, but salt will not.

Ray Tedder


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