Chemical Reactions
Lab
Name: _____________________
Date: _________
To prepare some of our favorite foods, such as birthday cakes, steaks, and even ice
cream, we rely on chemical reactions. Some of these reactions occur when food
ingredients combine, while others result from cooking or cooling processes.
For example when salt makes contact with ice, it starts a chemical reaction that transfers
heat energy from the surrounding environment. Adding salt to the ice changes the
freezing point of the ice (as you learned during our performance task). The lowering of
the freezing point is called freezing point depression.
An endothermic reaction is one in which energy must be provided in order for the
reaction to take place. In many endothermic reactions, so much heat is absorbed that the
container feels cold. Making Ice cream is an example of an endothermic reaction.
Ice cream is also an example of a colloid. Remember that a colloid is a homogeneous
mixture that does not settle out. The particles of a colloid are larger than those of solute
particles in a solution. In making ice cream, air gets trapped in the freezing cream, and
the ice cream becomes fluffy. Other examples of colloids are milk, clouds, Jell-O, and
butter.
In this lab, you will use salt and ice to start an endothermic reaction that will produce the
colloid: ICE CREAM!
Problem: What factors allow ice cream to be made and why is it considered a colloid?
Materials:
1/3 cup of ice cream mixture
6 Tbsp. of salt
1 gallon freezer baggie
ice
thermometer
1 pint or quart size freezer baggie
Procedure:
1. Fill a gallon freezer bag about ½ full of ice.
2. Add the 6 Tbsp. of salt to the ice.
3. In the quart/pint size bag obtain 1/3 cup of ice cream mixture from your
teacher.
4. Be sure to close the ice cream mixture baggie very well. (You do not want salt
in your ice cream!)
5. Place the bag of cream into the ice and salt mixture. Seal the bag.
6. Shake the bag well until the cream freezes.
7. Measure the temperature of the salt and ice mixture and record below.
8. Enjoy!
Data: Temperature of the salt and ice mixture: _______________
Conclusions:
1. Why is the inner bag filled less than halfway with cream?
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2. Why was the salt added to the ice? ________________________________
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3. How can you explain the water that results in the gallon baggie?
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4. What is freezing point depression? and How does it affect this lab? ____________
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5. Why is ice cream considered a colloid? ___________________________________
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6. Explain why this lab is an example of an endothermic reaction. _______________
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