Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Impurities and Boiling Point Depression
Name: Anand M.
Status: student
Age: 12
Location: N/A
Country: N/A
Date: Tuesday, March 18, 2003


Question:
Hello Thank you for your time. I am doing a science fair project on what impurities affect the boiling point of water. I am wondering what impurities can lower the boiling point of water. Salt, Sugar, Lemon Juice, and Baking soda all make it go higher but none of them make it go lower. I also can not use a vacuum and do not have the access to ethanol.


Replies:
Anand,

You will need some sort of water-soluble, low-boiling liquid like methyl alcohol -- it is available at a hardware store. Bear in mind, when an alcohol-water solution is heated to boiling, the vapor which boils off is not pure water or pure alcohol. To understand what I mean here, look up the word, "azeotrope," in a science reference book or search it out on the Internet.

Be especially careful if you attempt a proof of these ideas. Use a solution that has lots of water in it and only a little alcohol. Otherwise, you are facing a fire hazard. Please do your experiments under adult supervision. Good luck with your project.

Regards,
ProfHoff 623


Anand,

So far, you are doing a good job of making observations and measurements. The additives you have studied so far do not boil before water does, as ethanol would. (Could you expect that to affect your measurements?)

Is there any reason there should be something that makes water boil at a lower temperature?

Richard E. Barrans Jr., Ph.D.
PG Research Foundation, Darien, Illinois


ALL normally-behaving substances that are not volatile themselves MUST increase the boiling points of any pure solvents. The reasons for this are a bit involved to be explained here - but it's true. So all of the things you tested will increase the boiling point of water.

Some very volatile and water-soluble liquids, like ethanol or acetone, that evaporate very quickly can mix with water and "carry" the water along with them as they evaporate. Chemists frequently use a little acetone to "dry" glassware after it has been cleaned to remove the drops of water remaining. However, this is not "boiling" in the sense that the term "boiling" is used.

You can find some additional discussion on the NEWTON BBS web site at:

http://newton.dep.anl.gov/askasci/chem99/chem99241.htm

The "reason" why boiling points are always elevated is true involves the subject of "thermodynamics" -- which is the area that deals with how heat behaves.

Vince Calder



Click here to return to the Chemistry Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory