Follow the directions in the attached document – best to use more salt than directed. Be sure ice is straight out of the freezer. Include a photo of your experiment.
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ICE CREAM LAB
Adapted from http://www.thirteen.org/edonline/ntti/resources/lessons/s_freeze/freeze3.pdf
Have you ever wondered what it is about throwing salt on ice that makes it melt? And just why
does it melt? Where does the heat come from to melt the water? Why does it freeze again on the road
at night? These questions and many more about freezing and thawing will be looked at in this lab.
To start you off though lets talk about how energy flows in any system. When you studied the
air and weather you found that things always flow from areas of higher concentration to areas of
lower concentration. This automatic transfer of energy and material will always work to balance the
amount of energy and material. This is a natural law. From this we can deduce that heat energy will
always flow from areas of higher temperature to areas of lower temperature. Knowing this simple
rule, lets look at a very tasty application of it.
? 2 quart size Ziploc Freezer bags
? 1 pint of whole milk
? ½ – ¾ cup sugar
? 12-15 ice cubes (take out of the freezer just before using)
? 3 Tablespoons of salt
? 1 THOROUGHLY cleaned thermometer
? 2 clean plastic spoons
? 1 teaspoon vanilla extract
? Paper towels
? 3-4 ounce cups for final product
? Optional [ not recommended for first try]: 2 teaspoons chocolate syrup, or other flavors
1. Place ice cubes in one Ziploc bag and place thermometer among the cubes. Leave 30 seconds.
Record temperature of ice in data table.
2. (a) Place milk, sugar and vanilla in second Ziploc bag and record temperature. (b) Add flavoring
and record temperature.
3. Add 2 Tablespoons of salt in bag with ice. Seal & shake gently for 30 seconds. Record temperature.
4. Empty most of air from bag with milk/IC mix in it. Carefully seal this bag and place it inside the
bag with the ice mixture. Seal the outer bag tightly to prevent leaks.
5. Gently shake the sealed baggies back and forth in your hands to make sure that the ice mixture
coats the entire surface of the milk bag. Shake for 2 minutes and then carefully open the two bags and
take the temperature of the inner bag (IC mix) only (dont let any of the salty water get into this mix!).
Seal both bags. Keep shaking back and forth for 2 to 10 more minutes, recording the milk temperature
every 2 minutes until a solid product forms. Record final time and temperature.
6. Carefully remove the inner bag and place on paper towels. Wipe salty water from around opening.
Open baggie and squeeze solid product into two cups for final test.
7. Taste your product!
8. Clean up your work area and wash your hands.
NOTE: You might want to try making the homemade ice cream again sometime, varying some of the
ingredients (i.e., replace some of the milk with heavy cream, change the flavors, add a small pinch of
salt to the mix, add some egg or Eggbeaters® to the mix).
Temperature of ice in Ziploc bag
Temperature of milk
Temperature of flavor plus milk
Temperature of ice with salt added
Temperature of milk after shaking 2 minutes
12 15 minutes
?***RECORD some General Observations and Comments HERE:
Analysis & Application Questions
1. What happened shortly after you added the salt to the ice cubes (Step 3)? Was the temperature
above or below the freezing temperature for water?
2. What is the only factor that could have caused the changes shown in Question 1? What does this
tell you about the freezing point temperature of salt water compared to fresh water?
3. Heat energy is needed to change phase from a solid to a liquid. List the possible sources of the heat
needed for this phase change of the ice in your baggie. Which source do you think is the best
possibility and why?
4. In looking at the temperature changes shown on your data table, explain how the energy flow of
the baggie system resulted in your tasty treat for an end product. Where is the energy flowing from
and where is it going to?
5. In the radiator of your car you put a combination of antifreeze and water to keep your car engine
cool in the summer and prevent the radiator from freezing in the winter. Explain how you think this
works in terms of what you saw in the experiment you just did.
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