Ice Cream in a Bag

Materials

Needed for class of 30 students:
4 qts. (1 gal.) of milk (2% or reduced lactose milk will work)
4 qts. whipping cream (Rich's non-dairy coffee creamer works well and is less expensive)
8 cups of sugar
1 bottle vanilla
30 small plastic ziploc bags
30 large plastic ziploc bags (1 gal. size)
30 plastic spoons
crushed ice
rock salt or food grade salt
nuts, fruit or chocolate syrup if desired

Each student gets:
1 small plastic bag
1 large plastic bag
1/4 cup sugar
1/2 cup (120 mL) milk
1/2 cup (120 mL) creamer
1/4 teaspoon vanilla
1 plastic spoon
1/2 to 3/4 of a cup of rock salt
3/4 cup of crushed ice
 

Directions

1. Place 1/4 cup sugar into the small bag.
2. Fill the plastic cup to the 1/2 mark with milk. DO NOT TRANSFER IT TO THE BAG.
3. Add enough creamer (1/2 cup) to the milk to bring the total volume to 1 cup.
4. Add approximately 1/4 teaspoon of vanilla to the milk/creamer mixture.
5. Carefully transfer the contents of the cup into the small bag which contains the sugar. Close the bag securely.
6. Place the smaller plastic bag inside the larger bag.
7. Surround the smaller bag with several cups of crushed ice.
8. Pour 1/2 to 3/4 of a cup of salt over the ice and seal the larger bag securely.
9. Knead or roll back and forth on a table or desk top. Be careful not to put too much pressure on the bags.
10. After 10 minutes check the mixture to see if it is frozen. If not, continue kneading.
11. When the mixture is frozen, simply remove the smaller bag and eat the ice cream directly from the bag. (Add nuts, fruit or chocolate if desired.)
     

Purpose and background:

Ice keeps things cold because it absorbs heat energy from its surroundings. The freezing point of a liquid is the temperature at which it turns into a solid. In this activity the salt is added to the ice; it lowers the freezing point and the ice begins to melt.

In order for the ice to melt it must absorb heat energy from its surroundings (in this case the ice cream mixture). This causes the temperature of the mixture to drop and the mixture freezes.

 

For more information, check out:
http://www.sme.org/memb/neweek/actice.htm
http://www.col-ed.org/cur/sci/sci172.txt