Name ______________________________ Date _____________ Hour _______

Ice Cream Lab: Exothermic and Endothermic Reactions Ice cream has been a summer favorite for over a hundred years, especially in the

United States. Americans have the highest consumption of ice cream in the world, at over 23 quarts per capita per year! Ice cream became popular and affordable to Americans after the invention of a hand cranked ice cream churn by Nancy Johnson, which was patented in 1843. Prior to her device, ice cream was a treat only the wealthy could afford. Ice cream gets its creamy texture from the way the fat molecules, air bubbles, and ice crystals are combined within a highly concentrated mixture of sugar-water. Freezing too fast can cause the ice cream to be grainy, too slow and the ice cream will be soft. 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 ice begins to melt. The water and ice are at equilibrium at 0°C, but adding salt lowers the freezing point and thus lowers the equilibrium temperature. When you add more salt, the equilibrium temperature drops even lower. This is why salt is used to melt ice on roads during the winter. In order for the ice to melt, it must absorb heat energy from its surroundings. This causes the temperature of the mixture to drop, and the mixture freezes. Hypothesis: How does making ice cream demonstrate exothermic and endothermic reactions? Materials (per pair): ¾ c. whole milk 2T Whipping Cream 3T. sugar ¼ t. vanilla Quart zip-bag Gallon zip-bag

4 cups ice 4T. rock salt Gloves or towels Thermometer 2 spoons

Procedure: 1. Mix the whole milk, sugar, and vanilla in the quart bag. 2. Seal the bag tightly, allowing as little air to remain in the bag as possible. 3. Place the quart bag in the gallon bag and add the ice and salt. Again, let the air

escape and seal the bag tightly. 4. Wrap the bag in the towel or put your gloves on, and shake and massage the bag,

making sure the ice surrounds the cream mixture. 5. Watch the clock and record the temperature of the ice mixture every minute by

carefully opening a small area of the gallon bag and placing a thermometer into the ice/salt mixture being careful not to puncture the bag.

6. Record the temperature. Remove the thermometer and re-seal the bag. Continue shaking and massaging the bag until the ice cream begins to form a solid.

7. Record the last temperature and get you teacher’s permission to eat your experiment.

8. Create a graph of your data. Place the time on the x-axis, temperature on the y-axis. Be sure to include labels on your axes and a title.

Data Table

Time (min.)

Temperature (°C)

Analyze and Conclude: 1. Was your hypothesis correct? Why or Why not?

2. How does the graph support your understanding of endothermic and exothermic reactions?

3. How does this lab relate to the use of salt on roads in the winter?