Making
Ice Cream by Freezing Point Depression
Needed:
- 5 pounds of ice
- 2 pounds of salt
- large coffee can with lid
- baby food jar
with lid
- 1 cup of half & half
- 1/4 cup of sugar
- 1 tsp. of vanilla
- mittens
Experiment:
Dissolve 1/4 cup of sugar in 1 cup of half & half
and add 1 teaspoon of vanilla to the mixture. Fill a clean baby
food jar about two thirds full of the mixture and put the lid
on very tightly. Add two inches of ice to the bottom of a large
coffee can. Then add about a half inch of salt on top of the
ice. Add another layer of salt and ice so that your coffee can
is about one half full of salt and ice. Place your baby food
jar into the coffee can and layer more salt and ice until the
coffee can is almost full. Go outside, put on your mittens, and
roll the can around for fifteen to twenty minutes, periodically
adding more ice so that there is always ice in the can. After
fifteen or twenty minutes, remove your baby food jar and rinse
it off under cold water to remove the salt. Carefully open your
jar and taste the product of your experiment.
Explanation:
When a something is dissolved in
a liquid, the freezing point of the liquid is lowered.
The sugar added to the half & half makes the ice cream
mixture freeze at a temperature colder than 0oC (32oF).
Because of this, salt is added to the ice in your coffee
can. The salt combines with the ice water in the can and
lowers the freezing point of water, making the temperature
in the can far below 0oC (32oF). That's why you probably
want to use mitten to handle the coffee can! If the lid
comes off your coffee can while you are rolling it around,
simply add more ice and salt and continue with the experiment.
Make sure that you check your can every five minutes or
so to make sure that there is still ice inside. Without
ice, the temperature will warm up and actually melt your
ice cream. Share your ice cream with a friend and explain
to him or her how you made it.
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