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Chillin' Out with Freezing Point Depression
The Science of Making Ice Cream

data | hook | main | background & resources | student

Author Contact Information

Andre Wille
Basalt High School
600 South Side Drive
Basalt, Co 81621
awille@rof.net

Overview
In this lab students will learn about the relationship between salinity and the depression of the freezing point of water. While experimentally lowering the freezing point of water by adding salt, students will also make ice cream. This adds a special motivation for the students to succeed. To determine the salinity that results in the coldest temperature, a sample of the water is collected and evaporated. The mass of the salt is then used to calculate the molality of the solution. Student group data can then be used to plot a graph of molality vs. temperature. A formula to predict the theoretical molality using the molal freezing point constant can then be used to compare with the experimental value.

Grade Level/Discipline
10th or 11th grade Chemistry or Physical Science. Easy to simplify for Middle or Elementary classes.

National Standards
Standard A:Science as Inquiry/Abilities necessary to do scientific inquiry. Standard B:Physical Science/Structure and properties of matter.

Pre-activity set-up
Purchase necessary ingredients.
Locate plastic milk jugs to cut into trays.
Locate lab equipment.

Materials
For class of 25 in teams of 3

  • 5 gal Ice
  • 10 lbs Rock Salt
  • 15 plastic cups 8 Cut off 1 gal milk jugs or containers about the same size.
  • Plastic knives and spoons
  • 10 ml graduated cylinder
  • 8 petri dishes
  • Centigram Balance
  • Celsius thermometer

    Ice Cream Recipe

  • 1/2 gal Milk
  • 2 pints Cream
  • 1 cup Sugar
  • 1 tsp vanilla
  • 2 egg yolks
  • Mix all ingredients in pitcher to dispense to students.

    Time Frame
    This lab takes 1 to 1.5 hours to make the ice cream, collect the sample and set aside for evaporation. The following class period, water set aside in a petri dish to evaporate can be weighed and calculations completed.

    It is also possible to use a microwave to evaporate the salt the same day and complete lab in a 90 min session.

    Engagement and Exploration (Student Inquiry Activity)

    Explanation (Discussing)

    Elaboration (Polar Applications)

    Exchange (Students Draw Conclusions)

    Evaluation (Assessing Student Performance)
    Taste the ice cream !

    Check calculations, graph, lab write up if required.

    data | hook | main | background & resources | student