Making Ice Cream
Materials needed
 16 oz. (or greater) container with lid or cap
 2 cups ice
 1/4 a cup salt
 1 cup milk
 2 tbsp. sugar
 2-3 drops vanilla
 2 quart size sealable bags
 Duct tape
 Bowls
 Spoons
 Thermometer, preferably in Celsius
 Optional: ice cream toppings
Procedure
1. Place 1-1/2 cups of ice in the container, measure and record the temperature of the ice.
2. Add the salt to the container.
3. Shake the ice and salt mix for 30-60 seconds. Measure and record the
temperature.
4. In one of the sealable plastic bags combine milk, sugar, and vanilla. If using
flavored milk only add 1 tbsp. of sugar.
5. Seal the bag tightly, removing as much excess air as possible.
6. Put this bag inside the other sealable bag and again, remove as much air as
possible sealing the second bag.
7. Place the bag in the container and fill any extra space with ice.
Bag placed in container
with ice.
8. Cap the container and seal it tightly. If there is a chance of the lid leaking then duct tape around the
lid.
9. Shake the container for 15-20 minutes and check to see if the mixture has frozen. If not then pour
some water out of the container and add more ice.
10.
Once the ice cream has solidified take the bag out of the container and
shake off the water from it. If needed rinse the bag with cold water and dry it.
11. Unseal both bags and transfer the ice cream to a bowl, being careful that salt water
does not get into the ice cream.
12. Add toppings and enjoy!
This is what the final
product should look
like
Why does this work?
Making ice cream with ice and salt utilizes colligative properties. What are
colligative properties you ask? Well, first you need to understand what is going on at an atomical level. Salt is
an ionic compound of Sodium and Chloride, and is written like this: NaCl. An ionic compound is held
together because atoms are attracted to each other due to individual charges that they have because the
protons and electrons are out of balance in the atom. Electrons and protons are what make up an atom and
give it its individual properties. The number of protons that an atom has determines what element it is, for
example atoms with one proton are hydrogen atoms. A positive charged atom has one less electron than they
have protons, and a negatively charged atom has one more electron than protons. For example, sodium (Na)
atoms have a positive charge, which makes it attracted to chlorine (Cl) atoms that have a negative charge.
Water is a chemical compound of Hydrogen and Oxygen, which is written like this: H2O, because there are
two Hydrogen atoms for every Oxygen atom. When salt and water are mixed together the water dissolves the
salt, or NaCl, and breaks the salt up into its individual atoms, Na+ and Cl-. These atoms lower the freezing
point of water, the temperature at which water freezes, which is normally 0˚ Celsius. This means that instead
of water freezing at 0˚ C it freezes at a lower temperature. Essentially adding salt to the ice creates a “colder”
ice. The amount below zero that the freezing point of water is lowered depends on the amount of salt and ice
used. For this experiment using 1-1/2 cups of ice and ¼ cup of salt the freezing temperature should lower
approximately -10.6˚ C. The temperature of the ice is lowered allowing it to freeze the ice cream mix, because
the bag is surrounded by ice that is at a lower temperature.
Next Steps:
Try using a different ionic compound such as Calcium Chlorine (CaCl2) and see how that affects the
freezing temperature of ice!
Good Websites:
For ice cream
 http://www.food.com/recipe/homemade-ice-cream-in-a-bag-34257
 http://chemistry.about.com/cs/howtos/a/aa020404a.htm
For explaining the science behind it:
 http://antoine.frostburg.edu/chem/senese/101/solutions/faq/why-salt-melts-ice.shtml
 http://www.sci-experiments.com/ice_cream/saltwater.html