Ice Cream Science

Ice cream is partially frozen foam with an air content of 40 - 50% by volume. The foam consists of liquid and solid water (ice crystals) and fat globules; it exists as an emulsion, a stabilized mixture of immiscible droplets or particles. These experiments will look at the properties of ice cream when it is made by chilling it to the very low temperature of liquid nitrogen (-196 oC). In addition, the change of nitrogen from gas phase to liquid phase will be observed.

 

Materials

2 Stainless Steel large mixing bowls

2 Wooden Spoons

2 Measuring cups or Beakers

2 Cups Heavy Whipping Cream

2 Cups Half and Half

4 Cups Skim Milk

3 Tablespoons Vanilla

2 Cups Sugar

1 Small Dewar

1 5-Liter Dewar

5 Liters of Liquid Nitrogen Balloons

Racquet Balls

Ping Pong Balls

Tongs

Styrofoam or Plastic cups

Spoons

Napkins

 

Safety: Liquid nitrogen can cause severe burns. All participants in these experiments must wear goggles at all times. Anyone touching the metal bowl must be wearing cryogloves. Only experienced adult scientist should dispense the liquid nitrogen.

 

History

Folk tales claim that the cook of the French king Charles I was the first to invent ice cream in the early 1600s. Charles was so pleased that he wanted the recipe to be kept a secret, so the dessert could only be served at his table. The cook did not keep his promise of secrecy, and the recipe for ice cream spread widely.

 

What To Do

Conversion of gaseous nitrogen to liquid nitrogen

Blow into a balloon until it is approximately four inches in diameter. Fill the small dewar with liquid nitrogen. Place the balloon in the dewar. Cover the dewar and let the balloon remain there for 15 - 20 minutes. Use tongs to remove the balloon. Observe the balloon for a few minutes.

Questions

1. What is observable in the bottom of the balloon?

2. What happens as the balloon warms to room temperature?

Summary

 The air inside the balloon was cooled enough by the liquid nitrogen to change from gas to liquid. As the balloon warms up and begins to expand a small amount of liquid air should be visible inside the balloon. Since air is mostly nitrogen it is mostly liquid nitrogen that can be seen inside the balloon. The volume change associated with the phase change from gas to liquid is dramatic because the molecules in liquids are so much closer together than in gases.


Changing the properties of a racquet ball

Have a student bounce a racquet ball. Use tongs to place the racquetball in a dewar of liquid nitrogen. Allow it to remain there for 5 minutes. Ask students what will happen when the ball is removed and bounced again. Use tongs to remove the racquetball from the dewar. Away from the students, but still in their view, drop the ball on the floor.

Question

 1. Why did that happen to the ball?

Summary

The racquetball at room temperature bounces easily, but when it is cooled to liquid nitrogen temperature it becomes very hard and brittle. When dropped to the floor the ball shatters like glass.


Liquid nitrogen and ping pong ball behavior

With a small pin puncture a ping-pong ball by pushing it into the ball at an angle. Cool the ping-pong ball by immersing it in liquid nitrogen for a few minutes. Use tongs to carefully dunk the ball under the surface of the liquid. Use tongs to move remove the ping-pong ball and place it on a table or some other smooth surface. Observe carefully as the ball begins to warm up.

Questions

1. What is observable in the bottom of the balloon?

2. What happens as the balloon warms to room temperature?

Summary

The air inside the balloon was cooled enough by the liquid nitrogen to change from gas to liquid. As the balloon warms up and begins to expand a small amount of liquid air should be visible inside the balloon. Since air is mostly nitrogen it is mostly liquid nitrogen that can be seen inside the balloon. The volume change associated with the phase change from gas to liquid is dramatic because the molecules in liquids are so much closer together than in gases.


Conversion of gaseous nitrogen to liquid nitrogen

Blow into a balloon until it is approximately four inches in diameter. Fill the small dewar with liquid nitrogen. Place the balloon in the dewar. Cover the dewar and let the balloon remain there for 15 – 20 minutes. Use tongs to remove the balloon. Observe the balloon for a few minutes.

Questions

1. What is observable in the bottom of the balloon?

2. What happens as the balloon warms to room temperature?

Summary

The air inside the balloon was cooled enough by the liquid nitrogen to change from gas to liquid. As the balloon warms up and begins to expand a small amount of liquid air should be visible inside the balloon. Since air is mostly nitrogen it is mostly liquid nitrogen that can be seen inside the balloon. The volume change associated with the phase change from gas to liquid is dramatic because the molecules in liquids are so much closer together than in gases.


Source

"Chemical Demonstrations: A Handbook for Teachers of Chemistry." Vol. 3., Bassam Shakhashiri, University of Wisconsin Press, 1989.

"Science Is." Susan V. Bosak, Scholastic Press, 1991.

© S. Olesik, WOW Project, Ohio State University, 2002.