THE Ice Cream PHASE CHANGE LAB
Phase change - a change from one state (solid or liquid or gas) to another without a
change in chemical composition
Purpose:
• To investigate the effects of heat transfer on phase changes
• To investigate the effects of temperature changes on physical changes
Question:
How can this class cause a phase change to make ice cream from milk, sugar,
salt, vanilla, ice and salt?
Background Information:
In order to have a phase change in matter, heat must be gained or lost.
Phase changes occur all around us in everyday life. For instance, ice melts
when a drink is left in a room at normal temperature. Water freezes when
placed in a really cold temperature, as in the freezer. In this experiment, we
will see how fast heat is lost in order to change the milk from a liquid to a
solid state. This is also an example of a physical change in matter.
Hypothesis:
.
Materials:
• 1 cup milk
• ¼ cup sugar
• 1/3 cup + 1 tsp salt
• 1 ½ tsp vanilla
• ice
• measuring cups
• measuring spoons
• Ziploc bags (gallon and quart)
• Tape
• Towel
Procedure:
1. Place a dishtowel over your work area. Keep your work on your
towel.
2. Measure and pour milk, sugar and vanilla flavoring into the small
Ziploc bag. Carefully seal the bag, tape it closed and shake up the
mixture.
3. Put the small bag into the larger Ziploc bag.
4. In the large bag, add enough ice to cover the small bag and add the
salt.
5. CAREFULLY SEAL THE BAG!!!!
6. Take turns flipping the bag. Hold the bag by its corners. Keep
flipping over and over. Remember to keep the bag over the towel at
all times. It should take about 10-15 minutes to freeze.
7. When you have ice cream, take the smaller bag out and wipe it dry.
Dump the contents of the larger bag and into the bucket at your
station. DO NOT DUMP IT DOWN THE DRAIN!!!
8. Dish out the ice cream equally into the cups and ENJOY!
Conclusion Questions:
1. What state of matter was the milk when you began?
2. What state of matter was the milk when you were finished?
3. In order to change the phase of milk, what had to be removed?
4. What happened to the heat energy that left the milk?
5. Why was the salt added to the ice?
6. If you did not add the sugar would the ice cream have frozen faster?
7. Why did the outside of the bag get wet?
8. Heat energy is needed to change phase from solid to liquid. List the
possible source of the heat needed for this phase change. Which
source do you think is the best possibility and why?
9. Explain how the energy flow of the baggie system resulted in your tasty
treat for the end product.
The Thermodynamics of Ice Cream
Pure water freezes at 0.0 °C (32 degrees F) & boils at 100.0 °C (212 degrees
F). However, these values are changed by the presence of a solute (a minor
component such as sugar, salt, etc.) in water.
Adding a solute, like salt, to water raises its boiling point from 100 ̊C to
about 110 ̊C. The solutes dilute the number of water molecules at the
surface of the water & thus more energy is required for the water to turn
into a gas. This is called boiling point elevation. When you cook pasta in
salted, boiling water, it will theoretically cook faster since it’s cooking at a
higher temperature (110 ̊C vs 100 ̊C).
Adding a solute, like salt, to water also lowers the freezing point of water
from 0 ̊C to about -10 ̊C or lower, thus the salt water has a lower freezing
point than pure water and stays liquid at very low temperatures. When you
add salt (or any other substance...sand, sugar) to water, it interferes with
the orderly arranging of the water molecules into a solid and prevents the
hydrogen bonds from forming. This is called freezing point depression.
Here are some common examples of these effects: Antifreeze lowers the
freezing point and raises the boiling point of engine coolant (water). Salt is
used to melt ice on the roads & keep it from re-forming.. The greater the
concentration of the solute (salt), the lower the freezing point of water.
Definitions:
State of matter - the three traditional states of matter are solids (fixed
shape and volume) and liquids (fixed volume and shaped by the container) and
gases (filling the container)) "the solid state of water is called ice"
Solute - a minor component in a solution, such as sugar or salt in water.
Phase change - a change from one state (solid or liquid or gas) to another
without a change in chemical composition