PHASE CHANGES and ENERGY TRANSFER in Making Ice CREAM

Name: ______Period: ______Date: ______

GLO’s ______

HOM: ______

Introduction:

Do you know the process of making ice cream? The process of making ice cream involves chemistry concepts on phase changes and energy transfer. Phase changes of matter always involve change in thermal /(heat) energy. For example, to change a solid to a liquid state requires an addition or input of energy to the system. This process is called ______and this change (from solid to liquid) is called ENDOTHERMIC because they take in energy as heat from the surroundings.

The change from liquid to a solid state requires the removal of energy from the system. This process is called ______and the change is called EXOTHERMIC because energy is given off to its surrounding as heat.

The process of making ice cream also involves the concept of “LAW OF CONSERVATION OF ENERGY” which states that energy cannot be created or destroyed but may be transformed from one object to another. Thus, monitor the temperature changes from one Ziploc bag to the other Ziploc bag to understand this law.

Before you start, complete the table below as directed

ENDOTHERMIC Draw (like a ladder) the changes of matter EXOTHERMIC from solid -- plasma.

1..Question/Problem: ______

II. Hypothesis: ______III. Experiment:

A. Materials

2 - freezer bags 1-2 small plastic cup 1 pint of whole milk/ half & half 2 spoons 12-20 ice cubes paper towels 2 teaspoons of coarse salt/Hawaiian salt thermometer Sugar vanilla B. Procedure:

1.) Place ice cubes in a bigger Ziploc bag and place thermometer among the cubes. Leave 30 seconds. Record temperature of ice in data table.

2.) Place milk in second (smaller) Ziploc bag and record temperature. Record the temperature on data table.

3.) Add 2 tbsp (table spoon) of sugar and ¼ tsp (teaspoon) of vanilla in milk and measure the temperature then record it on data table.

4.) Add 2 teaspoons of salt in bag with ice. Seal and shake gently for 30-45 seconds. Record temperature on data table.

5.) Empty most of air from bag with milk in it. Carefully seal this bag and place it inside the bag with the ice mixture. Seal the outer bag tightly to prevent leaks. Shake the bag for 2 minutes. After 2 minutes, open the bag with milk and measure the temperature. Record it. Immediately seal the bags.

6.) Gently shake sealed baggies back and forth in your hands for 2 minutes to make sure that the ice mixture coats the entire surface of the milk bag. Then carefully open the 2 bags and take the temperature of the bag with the milk. Seal both bags immediately.

7.) Keep shaking back and forth for another 2 minutes, recording the milk temperature every 2 minutes until a solid product forms. Record final time and temperature.

8.) Carefully remove the inner bag and place on paper towels. Wipe salty water from around opening. Open the Ziploc bag and squeeze solid product into cups for final test.

9.) Taste your product.

10.)..Be sure to dispose of the ice mixture and left over product as well as spoons and paper towels.

11.)..Make sure your lab table and sink is clean and dry.

Data Table:

Procedure Step Description Measurement of Temperature (Celsius) 1 Temperature of ice in Ziploc bag 2 Temperature of milk 3 Temperature of milk with sugar and vanilla 4 Temperature of ice with salt added 5 Temperature of milk after shaking 2 minute 6 4 minutes 7 6 minutes 7 8 minutes 7 10 minutes 7 12 minutes 7 14 minutes

IV. Analysis and Discussion: Answer in complete sentences and organized it in a paragraph format.

What happened shortly after you added the salt to the ice cubes? Was the temperature above or below the freezing temperature for water? What is the only factor that could have caused the changes? What does this tell you about the freezing point temperature of salt water to fresh water?

What happened to the milk or half & half inside the baggie? What causes the milk/half & half to solidify? What is this process called? What type of change/reaction is this (exothermic/endothermic)? Explain.

What causes the ice cubes to turn to liquid? What is this process called? What type of change/reaction is this (exothermic/endothermic? Explain.

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 in your baggie. Which source do you think is the best possibility and why?

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. V. Conclusion (What did you find out from this lab? What did you learn from the process of making of making ice cream? Do you accept or refute your hypothesis. Explain. What are the errors you made from this lab and what did you do to correct those errors? If you were to do this lab again, what would you do to improve it?) ______