Name:
The Chemistry of Homemade Ice Cream
Background
Have you ever made homemade ice cream using a hand-cranked or electric ice cream
freezer? It’s a delicious activity, especially on a hot summer day. What is less obvious is
that making homemade ice cream provides excellent illustrations of some important
chemical principles. For instance, it is well wroth thinking about just why the ice cream
mixture (originally a liquid) freezes when surrounded by liquid water. Can you explain
that? You should be able to do so when this lab is over. Why do we add salt to ice?
Procedure
1. Obtain a CLEAN quart-size ziploc bag to hold your ice cream mixture and place all
the ingredients for your ice cream inside it. A suggested recipe is below:
1 cup milk
2 tbsp. sugar
dab of vanilla extract
some chocolate chips
2. Carefully seal our bag or your ice cream will be contaminated with salt and taste
horrible.
3. Mass out 2.0 – 3.0 moles of solid sodium chloride (rock salt). Record the exact mass
of the sodium chloride taken. Place sodium chloride in tennis ball container.
4. Return to your station.
5. Add ice to tennis ball container, filling about ½ way.
6. Place the ziploc bag inside the tennis ball container on top of salt and ice, fill with
ice, and put the lid on.
7. Shake and roll the tennis ball can vigorously to make the ice cream.
8. When your ice cream has solidified, measure the temperature of the ice-salt-water
mixture (NOT the ice cream) in the tennis ball can, then remove the ziploc bag, clean
up, and enjoy your ice cream.
9. If you find that your ice cream does not solidify, you can add more salt and/or ice
(you’ll have to decide) after recording the temperature of the original ice-salt-water
mixture.
10. CLEAN UP YOUR STATION!
Pre-Lab Questions
1.
2.
3.
4.
What is the mass of 2 moles of NaCl? 3 moles?
Will you expect the salt/ice mixture to be below, at, or above 0°C?
What will you do if your ice cream does not solidify?
What are some safety precautions you think you should take while doing this lab?
Data Table
Grams of salt initially added
Time needed for ice cream to freeze
Temperature of the ice/salt mixture
(*NOT* ice cream itself)
Post-Lab Questions
Answer questions on a separate sheet of paper.
1. Explain freezing point depression on a molecular level.
2. Which do you think should freeze faster, white milk or chocolate milk? Explain.
3. Why was the temperature of the ice-salt-water mixture NOT 0°C?
4. Why was sodium chloride added to the ice instead of sugar?
5. Using the article on road salt as a guide, how did the NaCl actually melt the ice
already present?
6. Write a balanced equation for the process of sodium chloride dissolving in water.
You do not need to include the water here, only the NaCl and the ions.
7. According to your equation, how many moles of particles are produced when 1 mol
NaCl dissolves in water?
8. Draw a diagram illustrating the process in which sodium chloride dissolves in water.