Reusable Cold Pack experiment

Objective: TO understand the concept of freezing point depression by making a reusable cold pack.

Materials:
Quart freezer bag
Isopropyl rubbing alcohol
Food coloring (Optional)

Safety Precautions: Isopropyl alcohol is poisonous if ingested. Be sure to clearly label the bag “POISON” before putting it into the freezer.

Procedure:
Add 2 cups of water and 1 cup of rubbing alcohol to a freezer bag and seal.
Place in the freezer overnight.
Observe the bag

Explanation
The solution in the bag will not freeze, because alcohol has a much lower freezing point then water. Isopropyl alcohol freezes at -89 C, and water freezes at 0 C. As a result, alcohol will depress the freezing point of the water. The temperatures in a typical freezer are not cold enough to freeze the solution.

The cold pack that was made in this experiment can be used whenever cold is required for an injury, such as to reduce swelling. IT can then be placed in the freezer and used over an over again.