Freezing Point Depression


Elementary/Middle School/High School/Higher Education Science Lesson Idea

Randy Yerrick - San Diego State University


The "Coolest" Lesson At School Today 

In this activity students investigated how salt lowers the temperature necessary to freeze ice to a solid (below 0’C) by directly measuring the temperature of a salt/ice mixture as they make ice cream in a zipped bag.


  1. Have you ever wondered how antifreeze works to protect engines from freezing solid in the winter?

  2. Or maybe you’ve wondered why road workers pour salt on the highway on winter mornings.

  3. Does the salt actually raise the temperature of the ice outside so that it melts?

Apple Education - Science Solutions

In this lesson, students are using the probeware included in Apple's Mobile Curriculum Lab for science to measure just what happens when rock salt is added to ice. In an attempt to explain how ice cream is made, students engage in a hands-on/minds-on activity in which they make predictions of the temperature before and after salt is added to packing ice surrounding their whole milk recipe. Students learned also how sodium chloride molecules inhibit the bonding between liquid water molecules and subsequently lowers the melting and freezing point of ice. Their reward...ICE CREAM!

Watch their video and hear their reflections on trying inquiry teaching in the classroom for the first time.

Click on the picture below to download the complete lesson plan idea.