Comments on: Salt Lowers Freezing Point of Water

By: Lexi

Lexi — Fri, 14 Oct 2011 02:43:25 +0000

This website was really helpful! I’m doing a science fair project on the ways to affect the freezing point of water, and I used this sight as my #1 referance! :)

By: David Bradley

David Bradley — Wed, 16 Mar 2011 09:53:40 +0000

Here’s an interesting twist for teachers to ask their students:

“Why would adding 10 grams of NaCl to water depress the freezing point more than it would elevate the boiling point? There are no wrong answers but keep in mind you’re talking about the motion energy of the molecules.

By: David Bradley

David Bradley — Thu, 11 Nov 2010 07:54:30 +0000

Under ideal conditions. It won’t be perfectly linear in real life.

By: Derrick

Derrick — Thu, 11 Nov 2010 02:48:16 +0000

Thank you,

Not sure what you ment, way above my relm of understanding but still thank you it was verry informetive. I belive what it boils down to (pun?) is that 5:1 = -16F for every 5parts water equal 1 part salt.

By: David Bradley

David Bradley — Wed, 10 Nov 2010 08:27:24 +0000

One can calculate the change in freezing point relative to the pure solvent using the equation:

Change = i * Kf * m

where Kf is the freezing point depression constant for the solvent (1.86 degrees Celsius per kg per mole for water), m is the number of moles of solute in solution per kilogram of solvent, and i is the number of ions present per formula unit (e.g., i = 2 for NaCl). This formula is approximate, but it works well for low solute concentrations. 10 grams of sodium chloride in 100 grams of water lowers freezing point to −5.9 Celsius. 20 g in 100 g of water would lower it to -16 Celsius, I believe. Seawater is about 3.5 g per 100 g so doesn’t freeze till about -2, but your suggested concentration is definitely going to kill your grass.

By: Derrick

Derrick — Tue, 09 Nov 2010 23:25:13 +0000

Question-s’
Do you know how what percent of salt is needed per measurable amount of water to keep it in liquid form at temperatures colder than 32° F?

Is there a percentage increase per decreasing degree, trying to keep water from freezing outdoors this winter (in 2 qt. containers) might get down to maybe 15° F below~ with out killing the grass?

By: David Bradley

David Bradley — Mon, 10 May 2010 07:46:03 +0000

Good question Aijaz, it’s all to do with energy.

You’re not adding salt to the icecream, you add it to the ice used to freeze the icecream ingredients. Ice has to absorb energy to melt. When you use ice to cool the ingredients for icecream, energy is absorbed from the ingredients. When you add salt to the ice, it lowers its freezing point so more energy must be absorbed to allow the ice to melt, which means the icecream ingredients get colder and themselves freeze.

Here’s a recipe for icecream that offers the same explanation – http://chemistry.about.com/cs/howtos/a/aa020404a.htm

By: aijaz

aijaz — Mon, 10 May 2010 05:36:17 +0000

ist of all i will thank u sir for giving such a attractive answer with attractive examples
sir as a collagativa property is the reason for it
but i don,t understand why is salt used in by the icecream sellers to keep the icecream freez in the summers {sorry for having gramatical errors as it was my first day on broadband net i was some how confused}

By: frank

frank — Wed, 05 May 2010 23:23:00 +0000

yo man this helped a ton with my science project….i hope i get an A+++

By: ben

ben — Mon, 19 Apr 2010 21:49:52 +0000

thank you this really helped me with my science project.