Observing, Describing and Measuring Changing Physical Properties: Making Ice Cream

Patty Phillips, Bancroft Elementary, Minneapolis, MN.
Based on original activities by
Anne Marie Helmenstine, Ph.D., About.com
How To Create an Endothermic Chemical Reaction (Safe)
http://chemistry.about.com/cs/howtos/ht/endothermic.htm
How To Create an Exothermic Chemical Reaction (Safe)
http://chemistry.about.com/cs/howtos/ht/exothermic.htm
Making Ice Cream in a Baggie
http://chemistry.about.com/cs/howtos/a/aa020404a.htm

Mary Lisa: Homemade Ice Cream
http://www.innovativeclassroom.com/lesson_plans/lessonplans.asp?id=12

Lori Hamlin: Making Ice Cream in 15 Minutes
Hamlin_lori@msmailDublin.k12.OH.US
Author Profile

Summary

Students will use science skills of observing, describing and measuring in the context of Making Ice Cream. Students will understand the concept that physical properties can change.

Learning Goals

Students will create an endothermic chemical reaction. Students will observe and describe the ingredients. They will measure the temperature of the milk and the ice. After making ice cream, students will measure the temperature of the ice cream (if thermometer is sanitized), and the ice/salt mixture. Students will observe and describe the changes in the physical properties of the ingredients. Students will taste the ice cream, and use their senses to describe the ice cream.

Context for Use

Primary (K-2) Classroom in an elementary school. Making ice cream can be a teacher demonstration or a hands-on activity for students. As a single lesson, plan 20-30 minutes.

I plan to teach this lesson as part of four lessons on endothermic and exothermic chemical reactions. Once students learn the difference between the two types of reactions, we will make ice cream, an endothermic reaction. The fourth lesson will be on photosynthesis, another endothermic reaction. This will tie in to our spring science unit Plants.

Lesson 1: How To Create an Endothermic Chemical Reaction (Safe), a teacher demonstration.
http://chemistry.about.com/cs/howtos/ht/endothermic.htm

Lesson 2:
How To Create an Exothermic Chemical Reaction (Safe)
http://chemistry.about.com/cs/howtos/ht/exothermic.htm

Lesson 3:
Making Ice Cream (the subject of this MNStep lesson plan). (See Activity Description for this lesson.)

Lesson 4:
What is Photosynthesis?, a new and learning objective for our spring science unit Plants.

References for Teaching Photosynthesis:
http://www.bbc.co.uk/gardening/gardening_with_children/didyouknow_photosynthesis.shtml

http://www.realtrees4kids.org/sixeight/letseat.htm

Subject: Chemistry:General Chemistry:Thermodynamics:Heat, Chemistry:General Chemistry:Thermodynamics, Chemical Reactions, Chemical Reactions:Endothermic & Exothermic Reactions
Resource Type: Activities:Classroom Activity:Short Activity:Demonstration
Grade Level: Primary (K-2)

Description and Teaching Materials

Materials:
1/2 cup milk
1/2 cup whipping cream (heavy cream)
1/4 cup sugar
1/4 teaspoon vanilla or vanilla flavoring)
1/2 to 3/4 cup sodium chloride (NaCl) as table salt or rock salt
2 cups ice
1-quart ZiplocTM bag
1-gallon ZiplocTM bag
Thermometer
Measuring cups and spoons
Cups and spoons for eating your treat!


Procedure:
Add 1/4 cup sugar, 1/2 cup milk, 1/2 cup whipping cream, and 1/4 teaspoon vanilla to the quart ziplocTM bag. Seal the bag securely.
Put 2 cups of ice into the gallon ziplocTM bag.
Use a thermometer to measure and record the temperature of the ice in the gallon bag.
Add 1/2 to 3/4 cup salt (sodium chloride) to the bag of ice.
Place the sealed quart bag inside the gallon bag of ice and salt. Seal the gallon bag securely.
Gently rock the gallon bag from side to side. It's best to hold it by the top seal or to have gloves or a cloth between the bag and your hands because the bag will be cold enough to damage your skin.
Continue to rock the bag for 10-15 minutes or until the contents of the quart bag have solidified into ice cream.
Open the gallon bag and use the thermometer to measure and record the temperature of the ice/salt mixture.
Remove the quart bag, open it, serve the contents into cups with spoons and ENJOY!

Explanation:
Ice has to absorb energy in order to melt, changing the phase of water from a solid to a liquid. When you use ice to cool the ingredients for ice cream, the energy is absorbed from the ingredients and from the outside environment (like your hands, if you are holding the baggie of ice!). When you add salt to the ice, it lowers the freezing point of the ice, so even more energy has to be absorbed from the environment in order for the ice to melt. This makes the ice colder than it was before, which is how your ice cream freezes. Ideally, you would make your ice cream using 'ice cream salt', which is just salt sold as large crystals instead of the small crystals you see in table salt. The larger crystals take more time to dissolve in the water around the ice, which allows for even cooling of the ice cream.

Teaching Notes and Tips

Alternative recipe:
For each student, put 2 packets sugar, 1 cup milk and 1 teaspoon vanilla into small ziplock bag and seal. Into a larger ziplock bag put 2 cups ice and 1 tablespoon rock salt. Put the smaller bag into the larger bag and seal.

The ice cream mixture will get very cold. Students may wear gloves or mittens. Another option is to put mixture into a tennis ball can or coffee can, instead of a large zip-lock bag.

Answering the Assessment questions may need to be guided by the teacher. Learning higher level vocabulary and concepts will generate interest in science and expand their background knowledge.

Assessment

1. Draw a diagram of the baggie-ice cream freezer. Add arrows to the diagram to indicate the direction of heat transfer (i.e. from the ice cream to the salt mixture or vice versa).
2. How many minutes did it take for your ice cream to freeze? What were the temperatures and temperature changes?
3. Was the process by which the milk mixture turned into ice cream endothermic or exothermic?
4. Describe the changes in the physical properties of the ingredients prior to and after making the ice cream.
Teacher will also make informal assessments using observations of students throughout the lesson.

Standards

1IIA1: Objects have physical properties.
1IB1: Observe, describe, and measure using a thermometer.

References and Resources