Endothermic Ice Cream!!

Have you ever wondered why salt is added to ice when you make your own ice cream? This activity explores the science behind making ice cream and looks at the behavior of ice melting and the affects salt has on the process to allow the phase change of cream from a liquid to a solid.

You will need:
Cream (half cream half milk) or whipping cream (heavy cream), sugar, vanilla, table salt (or rock salt), ice, large closeable bag, small closeable bag, gloves, thermometer
 

Now try this:

1. In the small closeable bag place ½ cup cream, ¼ cup vanilla, ¼ cup sugar and seal the bag securely.

2. In the large closeable bag fill ¾ with crushed ice and ¾ cup salt.

3. Place the small sealed bag into the large bag containing the salt ice mixture. Seal the large bag securely.

4. Wearing gloves move the bag gently mixing from side to side and shake up and down.

5. Continue mixing for 10-15 minutes until the contents inside the small bag have solidified into ice cream.

6. Using the thermometer, measure the temperature of the ice-water-salt mixture and the solidified ice cream and compare.

7. Eat and enjoy (you may add any additional ingredients you would like).

Explanation:
To make ice cream the cream mixture needs to change from a liquid to a solid. This process is called freezing (a phase change) and requires heat to be removed from the mixture. The surrounding ice melts at 0OC, and can bring the cream mixture to this temperature but won't freeze the cream. The addition of salt to the ice is needed for the phase change to take place. This is because salt lowers the melting point of ice and in this process requires heat from the surroundings (endothermic change). The surroundings that the heat is removed from to melt the ice is the cream mixture. This process is the required removal of heat from the mixture that allows for the phase change to take place and the cream mixture to freeze.