- University of Virginia
- Physics Department
A Physical Science Activity
Tasty Phase Change - The Ice Cream Lab
2003 Virginia SOLs
- Investigate the effects of temperature change on phase changes;
- Investigate the effects of changes in freezing point;
- Utilize these concepts in making ice cream.
Motivation for Learning
For homework the night before have students bring in an old towel, a pair of
water-proof warm gloves, and a plastic (grocery store or Wal-Mart) bag to take
everything home. Evoke prior knowledge of making homemade ice cream and ice
cream makers. (I like to use the following true/false question. Ice cream makers
use salt in the outside cylinder to decrease the friction as the cylinder turns
around. The answer is false because the salt is used to lower the freezing point
of the mixture inside.)
In order to have a phase change in matter heat must be either gained or lost.
Phase changes occur all around us in everday life. For instance, ice melts when
a drink is left in a room at normal temperature; conversely, water freezes when
place in a really cold temperature (the freezer). In this experiment we see
how heat is lost in order to change the milk from a liquid state to a solid
state. This is also an example of a physical change in matter.
Students will also be able to observe how adding solute (ice cream salt) to
a solvent (ice) changes the physical properties of that solvent. In this case
the freezing point of the ice is lowered allowing for the milk to turn into
For a group of about 150 students this lab cost around $35- $40.
To print out the Student Copy only, click
- 240 mL milk
- 45 mL sugar
- 80 mL ice cream
- 2.5 mL vanilla or chocolate flavoring
- 50 mL beaker
- 100 mL graduated cylinder
- 400 mL beaker
- 3.8 L zipper bag (gallon); freezer quality
- 0.95 L zipper bag (quart); freezer quality
- dish towel
- Celsius thermometer
- Find a partner to work with.
- Place a dishtowel over your work area. Keep your work on the towel.
- Pour 240 mL milk, 45 mL sugar, and 2.5 mL vanilla or chocolate flavoring
into the 0.95 L zipper bag. CAREFULLY seal the bag and shake up the mixture
- Put this small zipper bag inside the much larger 3.8 L zipper bag.
- In the 3.8 L bag add enough ice to cover the 0.95 L bag and add 80 mL of
ice cream salt. Take the temperature of the ice:______ C
- CAREFULLY SEAL THE BAG!
- Put your gloves on and get ready to make a phase change!
- Take turns flipping the bag. Hold the bag by its corners. Keep the bag flipping
over and over. Remember to keep the bag over the towel at all times. It should
take 10 to 15 minutes to freeze. Take the temperature of the ice/water mixture
again: ________ C
- When you have ice cream, take the smaller bag out and rinse it off with
cold water. One partner needs to take the larger bag and it's contents to
the trash bag. DO NOT DUMP IT DOWN THE SINK!!!
- Dish out the ice cream equally into the cups, and ENJOY! (You may rinse
the cup out and use it for water if you are thirsty.)
- Please clean up your area. (Leave it neater than you found it.)
Student Questions are included on the Student Copy of the activity. To print
out the Student Copy only, click here.
Answer the following on a separate sheet of paper:
- What state of matter was the milk when you began?
- What state of matter was the milk when you were done?
- In order to change the phase of the milk, what had to be removed?
- What happened to the heat energy that left the milk?
- Why was the salt added to the ice?
- If you did not add sugar would the ice cream have frozen faster? Why?
- Why did the outside of the bag get wet? (Assume that your bag did not spring
Students with Special Needs
Each student should be able to participate in this activity.
Click here for further
information on laboratories with students with special needs.
Did the student make ice cream? Was the student able to answer the lab questions
and comprehend the scientific principles behind the lab?
Take time to go over the answers to the questions on the students' sheet:
- The milk was in the liquid phase of matter when we started.
- The milk was in the solid state of matter when we finished.
- In order to change the phase of the milk we had to remove heat.
- The heat energy that left the milk went into the surroundings.
- Salt was needed in order to lower the freezing point of the mixture inside.
- Yes, the ice cream would have frozen faster without sugar because the sugar
lowers the freezing point.
- The outside of the bag was wet from condensation.
If time allows have the students convert the recipe from the metric system
to the standard system.
Why is salt spread on the roads before a winter storm?
*Salt is added to the roads in winter in order to lower the freezing point
of the precipitation and allowing it to melt and not stick on the roads.