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GK-12 Sensors!
Portable Module


Title: Freezing Point Depression

Author: Lester French, based on an activity supplied by the University of Maine Cooperative Extension, courtesy of Laura Wilson.

Discipline: Middle school science; High school physical science; High school technology

Objective: The objective of this module is to teach students about the physical and chemical properties of water. Specifically, the students will:

  1. Understand the three phases of water
  2. Understand how salt affects the three phases
  3. Understand basics of water chemistry (H2O and its partial polarity), why salt dissolves and cools the ice/brine solution below 0 C.

Associated Maine Learning Results

Science and Technology

E.4. Describe how a substance can combine with different substances in different ways, depending on the conditions and the properties of each substance.
E.5. Describe how the motion of the particles of matter determines the state of that matter (e.g., solid, liquid, gas, plasma) and vice versa.

Materials

  • 1-gal. Ziploc® bag or equivalent
  • 1-qt. Ziploc® bag or equivalent
  • 1 cup half and half
  • dash of vanilla extract
  • 2 cups ice cubes
  • ½ cup salt
  • ¼ cup sugar
  • cooler
  • thermometer or temperature probe
  • cups
  • spoons

Procedure

  1. Mix half and half with sugar and vanilla in 1-qt. Ziploc® bag or equivalent, seal the bag, and place in cooler.
  2. Put ice in 1-gal. Ziploc® bag or equivalent and measure the temperature of the ice and record. Put the bag of ice in cooler.
  3. When ready, add the salt to the bag of ice.
  4. Place 1-qt bag inside 1-gal. bag of salted ice and seal the bag of ice.
  5. Shake the bag.
  6. After shaking the bag for 5 minutes measure the temperature of the brine mixture and record.
  7. Describe what is happening.
  8. After another 5 minutes the solution in the 1-qt. bag should be frozen. If not shake for 1-2 minutes longer.
  9. Serve the ice cream into cups and eat.

Notes to Fellows/Implementors

  • You should start with the Microsoft PowerPoint presentation Freezing Point Depression, modified for your classes.
  • Explain the physics and chemistry of water.
  • Discuss why salt is used on roads.
  • Encourage students to do this with parents at home.
  • Despite what is better for making ice cream in a commercial ice cream maker use table salt rather than coarser kosher salt or rock salt. For the small volume of ice cream and the short time for freezing, table salt lowers the temperature further in 10 minutes.

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