Freezer bag ice cream

A chemistry experiment with a treat at the end!

Warm summer days call for a nice frozen treat for a snack. Ice cream has been made for many years and it is actually an example of some pretty complicated chemistry. Try this fun activity with children for hands-on work with energy concepts.

Safety note: Be sure to explain safety precautions to children. This experiment uses ice at a low temperature, so gloves or towels may be called for. Measuring devices should not be mixed between substances. Before and after this experiment, be sure to thoroughly clean hands. Disclaimer: All information provided on this site is for entertainment and education purposes only. Using any information from thecasabouquet.com is at your own risk.

Instructions

Set up assembly line stations on a long table or countertop: Quart bags, sugar, milk, vanilla, gallon bags, ice, salt. 

Adults can measure and give ingredients to the children as they pass down the line OR give the children practice with measuring by asking them to measure and pour as they go down the line (this will take longer and make more mess, but it may be worth it.)

Put two quart bags together. Pour sugar, milk, and vanilla into the inner one. Seal tightly.

Put two gallon bags together. Pour ice into the inner one. Measure the temperature of the ice. Sprinkle with rock salt. Measure the temperature of the ice with salt. Put the sealed quart bags into the ice bag and seal tightly.

Go outside (if possible) and shake, roll, or toss your bag! Be sure to keep it moving, it will be very cold on your hands. The soft ice cream should form within 7 to 15 minutes.

Remove the quart bags and dry off. Measure the temperature of the ice-salt-water. Open the ice cream bag and use a spoon to enjoy!

Dispose of the salt-ice-water appropriately and dispose of the bags.

Discuss the mechanical energy each child is putting into the freezer bag ice cream making. How does a person get energy to do the work?

What happens to the temperature of the ice at each point? How does the salt help in making the milk mixture freeze? Is the milk bag transferring energy to the ice bag? Or vice versa?

Supplies

(per person)

• ½ cup cold milk
• 1 tbsp. sugar
• 1/4 tsp. vanilla
• ¼ cup rock or ice cream salt
• 3 cups ice
• 2 quart size freezer reclosable bags
• 2 gallon size freezer reclosable bags
• paper towels
• spoon
• towel or gloves
• thermometer or Vernier LabQuest with temperature probe
• paper or notebook for recording results, pen

Notes for scaling up: 4 lb. bag of sugar has 151 tbsp.; ½ gallon of milk makes 16 half-cups; 10 lb. bag of ice should make 4 or 5 servings; 4 lb. box of ice cream salt makes about 38 servings

What is the science?

Content: states of matter, freezing point, energy transfer, mechanical energy, thermal energy, work

Ice cream is a frozen mixture that is classified as a colloid. Shaking the mixture could actually cause the temperature to rise. By placing it in ice, this energy causes the ice (solid) to melt. Water (liquid) freezes at 0^oC. Salt causes the freezing to happen at a lower temperature, known as freezing point depression. Ice in my home freezer is -15^oC. Salt helps keep the temperature in the ice cream process lower. You may want to experiment with trying to make ice cream again without the salt and see what happens to the temperature, the amount of ice, and how fast the ice cream freezes. If the children are familiar with the idea of using salt on sidewalks and roads in the winter, this experiment can help with discussing the process. You can also use this experiment to introduce Fahrenheit – Celsius conversion.

Resource links

• http://www.sciencebuddies.org/science-fair-projects/project_ideas/FoodSci_p013.shtml#background
  • Chemistry of Ice Cream Making: Lowering the Freezing Point of Water
• https://www.mathsisfun.com/temperature-conversion.html
  • Conversion of temperature from Math is Fun
• http://www.vernier.com/products/interfaces/labq2/
  • LabQuest2 from Vernier Software & Technology
• http://www.foodtimeline.org/foodicecream.html
  • Ice cream from Food Timeline
• https://www.monticello.org/site/research-and-collections/ice-cream
  • Thomas Jefferson and ice cream from Monticello
• http://www.flinnsci.com/teacher-resources/safety/general-laboratory-safety/
  • General Lab Safety resources from Flinn Scientific. Be sure to check out the Student Safety Contract.

Let’s talk story

During summer camp, this is one of the favorite energy activities for children. It’s always good to do this on a hot, summer day, let the children do all the shaking outside and then take a relaxing break with a snack they made. The vanilla is good this way, but some folks like to add a little chocolate syrup or mini chocolate chips at the end. [Note in my photo the cute little dinosaur sprinkles!]

Ice cream is a very popular American treat and it’s interesting to look up the history. There are many legends, but a lot that’s not really known about the origin. Ice cream without eggs is known as “Philadelphia style”. The first printing of an American recipe was in 1792. Thomas Jefferson brought a recipe home from France with him and made it a regular dessert at Monticello and the White House. His recipe calls for a sabottiere, which was a small metal container that was hand-turned in the ice-salt bath. The cranking ice cream maker was patented by Nancy Johnson in 1843.

I’ll be looking for comments below, or contact me at lisa [at] casabouquet[dot]com.

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