Water's boiling point and table salt

ethomas

I was doing a simple experiment with my class to demonstrate the boiling point of water.Two of the students wanted to see what would happen when we added salt. So, the students added about 50 ml of common table salt to less than 200 ml of boiling water. The temperature of the water immediately jumped from 215 degrees Fahrenheit, to 226 degrees Fahrenheit. I read in another thread that salt lowers the boiling point of water. Is that true? Or does it increase the boiling point? And why is this? Please use simple language as I am years past my high school chemistry class and was never very good at chemistry anyway (in college I passed only thanks to the wonderful curve!).

mrjeffy321

Salt both lowers the freezing point and raises the boiling point of water.

Pure water, at sea level, boils at 100 degrees celsius (212 F). Once water begins to boil, it stops increasing in temperature, after which, all the energy that is trying to heat the water up is goin g into boiling it.
So when you dissolved all that salt into the already boiling water, you raised the boiling point, allowing the water to get hotter than it normally would have without the salt. The same is true for cooling water, salt water can get much colder without freezing into ice than pure water.

ethomas

Thanks for your reply- it was very helpful.