Teaching Physical Change by Making Ice Cream

Materials:
1 quart size freezer bag
ice cream mixture
1 sandwich size plastic bag
ice
salt
spoons and cups

Ice Cream Mixture: Whole milk or Half and Half, sugar, vanilla flavor. Approximately 1/2 sugar to a quart of milk. You can increase or decrease the sugar and still get a tasty mixture.

Procedure:
1. Inside the sandwich bag, pour the ice cream mixture.
2. Describe the physical characteristics of the mixture? Taste the mixture.
3. Press out as much air as possible before sealing the bag.
4. Measure the temperature of the ice. Measure the temperature of the ice after the salt has been added.
5. Submerge the bag beneath the ice, salt mixture. Gently shake the bucket until the mixture becomes solid. How long do you think this will take? What was the actual time?
6. Remove and open the bag.
7. What are the physical characteristics of the milk now?
8. Remove the mixture with a spoon into individual cups and taste the mixture. Describe the taste and texture:
9. Was this a physical change or chemical change? How do you know?
10. Why does frost form on the outside of the bucket?
11. What conditions are necessary for making ice cream?
12. Why did you have to shake the mixture?
13. Why do you think the temperature of the ice drops below freezing when you add salt?
Answers:
9. physical change, The mixture melts into what it originally was.
10. Condensation of water from the atmosphere occurs on the bucket. The condensation freezes because the temperature is below freezing point.
11. Sub-freezing temperatures.
12. To prevent ice crystals from growing in the ice cream mixture.
13. The salt causes the ice to melt. The energy has to come from somewhere and it comes from the ice. The ice may be 0 degrees Celsius or 32 degrees Fahrenheit. However, when it gives up that energy for the ice to melt, the temperature drops to about -8 to -10 degrees Celsius.