Chemistry lab yields tasty results

Homemade ice creamAfter finishing the chapter on solutions, chemistry students set their class lessons to work by making ice cream using milk, salt, vanilla, sugar, ice and Ziploc bags.

“The purpose of the lab was to demonstrate freezing point depression, which is a colligative property,” said Science Teacher Michele Purrington. "Also, milk and ice cream are both colloids, which is a type of mixture in which one substance is evenly dispersed in another, meaning nothing settles to the bottom. Specifically they are both emulsions."
 
In order for the ice cream to form, a temperature of -5 to -10 degrees Celsius was necessary. The salt lowered the temperature of the salt-ice water mixture because the freezing point of the solution was lower than the freezing point of the plain water. When the salt dissolved in the water, it lowered the temperature at which the solution froze. The amount that the freezing point reduced was the freezing point depression.
 
“The lab demonstrated the principles that the kids were learning in class. They were able to experience what they were learning in the book first-hand,” said Purrington.
 
Here's how you can recreate this tasty science experiment at home...
  1. Mix together 1 cup of whole milk, ½ teaspoon of vanilla and ¼ cup of sugar in a quart-sized Ziploc freezer bag.
  2. Then placed that bag inside of a gallon-sized Ziploc bag filled halfway with ice and ½ cup of rock salt (you can substitute Kosher salt if you do not have rock salt).
  3. Then shake the bag vigorously or toss it between two people (we recommend doing this outside to avoid a potential mess).
  4. When ice cream is firm it is time to eat.