Why does salt make ice colder?

+51 votes
asked Jul 16, 2015 in Science by Natasja (900 points)
I have an ice cream maker and you have to mix salt with ice in the outside pail. The salt makes the ice stay colder, even though it seems to melt faster. I have seen that this actually works but I don’t understand the science behind it. What does the salt do to make the ice colder?

3 Answers

+19 votes
answered Jul 26, 2015 by Crow (1,020 points)
Adding salt to your ice in your ice cream maker actually causes the ice to melt. When water is freezing, it gives off heat (releases heat). When ice melts, it actually cools down. Water freezing gives off energy while an ice cube melting uses energy.

It may sound counter intuitive to most but that is just how it works. The salt helps the ice melt in a way that actually cools the water (and in your ice cream maker allows the water/ice to keep the cream cold like it needs to be).
+9 votes
answered Jul 17, 2015 by sthephanie (1,070 points)
Why does salt make ice colder? Salt needs to use energy to be dissolved into water. The salt actually uses the energy from the water. When salt takes the energy from water, it changes not only the melting point but also its boiling point. When you add salt to ice, it lowers its melting point making it colder. When you add salt to water that you plan to heat, the salt raises the boiling point.

I am no scientist so you would probably be better off reading a physical chemistry book to get the correct scientific answer.
+5 votes
answered Jul 18, 2015 by Taieb (1,130 points)
Salt actually lowers the degree to which the ice melts. It is a chemical reaction. The salt doesn’t actually “make” the ice colder but creates a chemical reaction between the H20 (water) and NaCl (salt) that lowers the melting point. This makes the ice last longer.

Try an experiment at home to see what I mean. Instead of your ice cream maker, get out two ceramic or glass bowls. Put ice in both bowls. Add salt to only one bowl. Feel the ice in both bowls every 15 minutes. The chemical reaction can easily be noticed.
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