Laboratory Investigation the Science of Ice Cream

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 17th 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:

 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:

 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

 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