Amazing Salt

Ruby Bell Park Manor
7037 South Rhodes
Chicago IL 60637
(312) 535-3070

Objectives: 1. To see what effect salt has on ice. 2. To have students get experience with the concept of freezing. 3. To see which way heat travels. 4. To have students manipulate variables. 5. To see the societal impact of freezing with ice and salt. Materials needed: (Equipment per group: 4-6 students) First experiment salt ice water 2-styrofoam cups 2-thermometers 2-test tubes a measuring cup or graduated cylinder 2-stirrers timer or minute-hand watch or clock 1-teaspoon Team Equipment 2-clean coffee cans (1 and 3 lbs.) 2 cups of Rock salt (NaCl) 2 quarts of crushed ice masking tape or duct tape mittens thermometer (that measures down to -20oC)

Ice Cream Recipe (Mix the following in the 1 lb. coffee can) 3 to 3 1/2 cups of half and half 3/4 cup of sugar 2 tsp. of vanilla extract Heat mixture to dissolve the sugar. DO NOT BOIL. Let the mixture cool.

Strategy: Fill two styrofoam cups 1/2 full with crushed ice. Place into each cup a test tube filled with 10ml of water. Place the thermometers in each cup. In one cup place two teaspoons of salt. Observe the temperature of each cup and record. For the next seven minutes, record the temperature in each cup each minute. Students should have observed that the test tube with the salt lowered the temperature of the salt water causing the water in the test tube to freeze. Team Ice Cream Procedure: Pour the cooled ice cream mixture described in the
materials section into the small can until the can is about 3/4 full. Put the
lid on and tape around the top securely. Place the smaller can into the larger
one. Put alternate layers of ice and salt so that the amount of ice is about
four times the amount of salt. Put on the lid. Place tape around it. Put on
the mittens. Have students sit in a circle and roll the can back and forth.
The ice will melt. When very little ice is left, you may add more ice with more
salt. After 20-30 minutes open the can and enjoy your ice cream. Check the
temperature of the water-ice-salt mixture with the thermometer.

When the salt dissolves, its particles interfere with the freezing process which
forms ice. Even though the temperature is 0oC, the ice can melt. Energy is
needed to melt the ice. This energy comes from the water. As a result the
ice and the water solution becomes colder, because the heat goes to the ice.
The mixture could go to about -15oC. As energy (heat) is removed from the ice
cream mixture, it gets very cold and the ice cream is formed.

Road salts (CaCl2) helps to melt ice by the same principle. The addition of salt
to ice lowers the freezing point of water.

REFERENCES: AIMS Education Foundation, 1987. Gardner, Robert, Kitchen Chemistry, 1980.

Guzdziol, Ed., lecture summer, 1993.

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