Does pure water reach its boiling point at a higher or lower temperature than Salted Water? and does the same apply to water saturated with sugar?

Asked by: Dave Burley

Answer

What a good question. Salt and sugar are common household substances to put into water to see what changes they can cause in the properties of water. I wonder what you think would happen? Do you think that if a little salt changed the boiling point temperature, would more salt change it more? Do you think that equal amounts of salt in one sample and sugar in another sample would have the same changed boiling point temperature? Have you thought about trying pepper? How about baking soda or orange juice?

Why not try these experiments out and see? Simply get a sample of pure distilled water and measure its boiling point temperature in your kitchen. You may have heard that water boils at 100 degrees centigrade. This is true if you are on earth at sea level. You may be in the mountains or in a deep valley, so find out at what temperature water boils in your kitchen.

This may be harder than it sounds like to actually do. You cannot use a thermometer made for taking body temperature, nor can you use one made for measuring outside temperature. If you can get one from your school science department that would be great. You can also use a candy thermometer.

Once you have gotten your boiling point temperature for pure distilled water in your kitchen try putting various substances into the water. Of course, you will try one thing at a time and you will always start with a fresh sample of pure water. Also you will be sure to use the same amount of each substance you try. After you go through all of your samples you may want to try it again with more or less of the sample material to see if the amount of the impurity affects the amount of change, if any, in the boiling point temperature.

It is good that you phrased your question in terms of 'higher or lower', some substances may raise the boiling point temperature and some may lower it.

I hope you actually are able to do this. I must warn you though, if you are not careful you might have fun and if you are really careless you might learn something!
Answered by: Tom Young, B.A. Science teacher, Whitehouse High School