Posted by: tpsciencefun | January 26, 2012

Ice Cream Science

Posted by overwhelming demand, here is the fun recipe we followed to experiment with physical phase changes in fifth grade chemistry.

Yum-yum…have some fun!!

Materials

  • 1/2 cup milk
  • 1/2 cup whipping cream (heavy cream)
  • 1/4 cup sugar
  • 1/4 teaspoon vanilla
  • 1/2 to 3/4 cup sodium chloride (NaCl)  or rock salt
  • 2 cups ice
  • 1-quart Ziploc bag and 1-gallon Ziplocbag
  • Thermometer
  • Measuring cups and spoons
  • Cups for eating your treat!

Procedure

  1. Add 1/4 cup sugar, 1/2 cup milk, 1/2 cup whipping cream, and 1/4 teaspoon vanilla to the quart ziploc bag.
  2. Seal the bag securely.
  3. Put 2 cups of ice into the gallon ziploc bag.
  4. Use a thermometer to measure and record the temperature of the ice in the gallon bag.
  5. Add 1/2 to 3/4 cup salt (NaCL) to the bag of ice.
  6. Place sealed quart bag inside the gallon bag of ice/salt.
  7.  Seal the gallon bag securely.
  8. Gently rock the gallon bag from side to side. Hold by  top seal with cloth  between the bag and your hands.
  9. Continue to rock the bag for 10-15 minutes or until the contents of the quart bag have solidified into ice cream.
  10. Open the gallon bag. Measure and record the temperature of the ice/salt mixture.
  11. Remove the quart bag, rise with cold water, open and serve! ( When you  take the smaller bag out, rinse it off with cold water. One partner needs to take the larger bag and it’s contents to the trash or outside. DO NOT DUMP IT DOWN THE SINK!!!)

Why it works:

Explanation For Salt and Ice Cream Experiment:

Ice has to absorb energy in order to melt, changing the phase of water from a solid to a liquid. When you use ice to cool the ingredients for ice cream, the energy is absorbed from the ingredients and from the outside environment (like your hands, if you are holding the baggie of ice!). When you add salt to the ice, it lowers the freezing point of the ice, so even more energy has to be absorbed from the environment in order for the ice to melt. This makes the ice colder than it was before, which is how your ice cream freezes.

Compounds that break into two pieces upon dissolving, like NaCl breaks into Na+ and Cl, are better at lowering the freezing point than substances that don’t separate into particles because the added particles disrupt the ability of the water to form crystalline ice. The salt causes the ice to absorb more energy from the environment, becoming colder.

Recipe Variations

  • Chocolate Ice Cream: Reduce vanilla  and add two squares of melted, unsweetened baking chocolate to the mixture.
  • Strawberry Ice Cream: Reduce vanilla and add strawberries after mixing the ice cream.
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