Name: ____________________________
Block: _________ Date: _________________
Laboratory Investigation – The Science of Ice Cream
The effect of salts on freezing was known in the 13th-century Arab world, and that knowledge eventually
made its way to Italy, where ices made from fruit were described in the early 17 th century. The English term
“ice cream” first appears in a 1672 document from the court of Charles II.
Excerpted from On Food and Cooking by Harold McGhee
There are a number of chemistry-related concepts that can be studied as part of making ice cream
including:
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Colligative properties, specifically freezing point depression
The enthalpy (∆H) of freezing and melting
Chemical composition/properties of milk and cream
Example of organic molecules - flavorings
The first step is the most important: Start making the ice cream!!!
Safety:
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Wash hands
There should be no direct contact of any of the ingredients with any surfaces
Report any spills to the teacher
Clean-up after you finish
Materials
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1/2 cup milk
1/2 cup heavy whipping cream
1/4 cup sugar
1/4 teaspoon vanilla extract or vanilla flavoring
1/2 to 3/4 cup sodium chloride (NaCl) as table salt
2 cups ice
1-quart ZiplocTM bag
1-gallon ZiplocTM bag
thermometer
measuring cups and spoons
plastic spoon for eating the ice cream
Procedure
1. Carefully 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.
2. Put 2 cups of ice into the gallon ziplocTM bag.
3. Add 1/2 to 3/4 cup salt (sodium chloride) to the bag of ice.
4. Place the sealed quart bag inside the gallon bag of ice and salt. Seal the gallon bag securely.
5. 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.
6. Continue to rock the bag for 10-15 minutes or until the contents of the quart bag have solidified into
ice cream. BE PATIENT, the contents will solidify.
7. Open the gallon bag and use the thermometer to measure and record the temperature of the ice/salt
mixture.
8. Remove the quart bag, open it, and enjoy the contents.
9. Clean up!!!
Some Background
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; this makes the ice/water mixture that forms colder than it would
otherwise be, 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.
You could use other types of salt instead of sodium chloride, but you couldn't substitute sugar for the salt
because (a) sugar doesn't dissolve well in cold water and (b) sugar doesn't dissolve into multiple particles,
like an ionic material such as salt. Compounds that break into two pieces upon dissolving, like NaCl breaks
into Na+ and Cl-, are better at lowering the freezing point than substances that don't separate into particles
because the added particles disrupt the ability of the water to form crystalline ice. The more particles there
are, the greater the disruption and the greater the impact on particle-dependent properties (colligative
properties) like freezing point depresssion, boiling point elevation, and osmotic pressure.
Lab Questions
1. What happened to the ice/salt mixture around the ice cream as the ice cream solidified?
____________________________________________
2. Is melting an endothermic or exothermic process? __________________
3. Where did the energy come from to melt the ice/salt mixture? ___________________
4. What happens to the melting/freezing point of a liquid when a solute like salt is added to it?
_________________________________________
5. What is this colligative property called? _______________________________
6. Why does a solute like NaCl lower the freezing point of a solvent?
_____________________________________________________________
7. What was the temperature of the ice water when you measured its temperature? _______
8. What would the “normal” temperature be of a mixture of ice and water in equilibrium with each
other? _______
Milk, Cream, and Ice Cream (you may need to use a computer or your phone to look up some of these
answers)
1. What is an emulsion or colloid? ______________________________________
___________________________________________________________________
2. Would you describe milk as an emulsion? Why? __________________________
__________________________________________________________________
3. What are some other common examples of foods that are emulsions?
__________________________________________________________________
4. Milk is mostly comprised of what chemical? ________________
5. What is suspended in the milk to give it the opaque “milky” appearance? __________
___________________________________________________________________
6. In addition to fat, what are some other key ingredients/components of milk?
______________________________________________________________________
7. What percentage of the world’s population is estimated to be lactose intolerant? _____
8. What is the typical fat content of whole milk? _______________
9. What is the typical fat content of heavy whipping cream? ___________
10. We used 50% whole milk and 50% heavy whipping cream so what is the approximate percentage
fat in our ice cream mixture?
__________________________________________________________
11. What are the total calories in our serving of ice cream?
Flavorings
Vanilla Flavoring
Vanillin, an organic compound, is the main chemical component in natural vanilla extract. However, natural
vanilla extract is actually a mixture of several hundred different compounds in addition to vanillin. Artificial
vanilla flavoring is a solution of pure vanillin, usually of synthetic origin. The structure of vanillin is shown
below along with the structure of some other flavorings
What is the chemical formula for Vanillin (check on how to count the carbons and
hydrogens that aren’t written explicitly:
_____________________
Vanillin
Look at the table below at the ester-based flavorings. An ester is a specific
“functional group” in organic molecules. What general structure do you see as
parts of all of the ester-based flavorings?
__________________________________
Ester-Based Flavorings
Oil of Wintergreen
Cinnamaldehyde