Virginia T. O'Brien - Higgins Community Academy
We All Scream For Ice Cream
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Virginia T. O'Brien Higgins Community Academy
11710 S. Morgan
CHICAGO IL 60643
Demonstrate freezing point depression, one of the colligative properties.
One large and one small zip lock baggie, one thermometer and one spoon for
each student; granulated sugar, vanilla, a variety of milk products (skim, 2%,
whole, chocolate, and cream), measuring cups, measuring spoons, vanilla
extract, salt, ice cubes, chocolate syrup.
Speculate as to what occurs when sodium chloride or calcium chloride, types of
salt, is sprinkled on icy streets and sidewalks. Students may think they cause
the temperature to rise. Give each participant a small and a large zip lock
baggie and a thermometer. Fill large baggie half full with ice. Place
thermometer in baggie, seal the baggie and set it aside. In small baggie, put
4 oz. of a milk product, 1 tbs. granulated sugar, and 1/4 tsp. of vanilla.
Press air out of baggie, seal it, squeeze it to dissolve the sugar and set it
aside. Record the temperature on the thermometer through the bag in the large
baggie, making sure that the tip of the thermometer is in the ice. Take the
thermometer out of the baggie. In large baggie add 6 tbs. of table salt, sodium
chloride, to the ice. Seal and shake for a short time to mix up the salt and
ice. Place thermometer back in the large bag, in the salt ice mixture, and
after 3 minutes, record the temperature as before. Remove the thermometer.
Place small baggie inside of large baggie. Push some of the air out of the
large baggie and seal. Vigorously shake the baggies for about 5 minutes. Take
small baggie out of big bag, observe the consistency of the mixture, and if so
desired, eat it.
It should be observed that sodium chloride lowers the freezing point of the
ice/water mixture and helped change the physical state of the milk mixture into
homemade ice cream. For this reason, calcium chloride and sodium chloride are
used to deice sidewalks and streets, but if the outdoor temperature falls below
this new freezing point, ice will still form.
Participation and following directions. Carefully reading and recording the
two thermometer temperatures and making and recording careful and accurate
At the end students will be able to understand that salt lowers the freezing
point of water/ice and that this principle underlies the deicing ability of
salt as well as its use in making ice cream.