ICE CREAM THERMODYNAMICS LABName

PROBLEMS:

1) How are the 1st and 2nd laws of thermodynamics illustrated when making ice cream?

2) Is making ice cream a physical or chemical change?

3) How can you lower the freezing point of water in order to freeze an ice cream mixture?

FORM HYPOTHESES: ______

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CONDUCT THE EXPERIMENT

MATERIALS:

ICE CREAM MIXTURE:

  • Quart size Ziploc bag
  • ½ cup (120 ml) of milk.
  • ½ cup (120 ml) of half half /whipping cream.
  • ¼ cup (60 ml) sugar.
  • ¼ teaspoon vanilla.

MAKING THE ICE CREAM MATERIALS:

  • Gallon size Ziploc bag
  • Ice
  • Rock salt
  • Thermometer

PROCEDURE:

PART 1 {Mixing the Cream}:

  1. Add ingredients to smaller size Ziploc bag.

  • a. ½ cup (120 ml) of milk.
  • b. ½ cup (120 ml) of half half
  • c. ¼ cup (60 ml) sugar.
  • d. ¼ teaspoon vanilla.

  1. Seal the bag well. Try to make sure all of the air is out of the bag.
  2. Mix the ingredients until they are blended.
  3. Take the initial mass of the milk mixture (and bag) and record in your data table.
  4. Take the initial temperature of the milk mixture by wrapping the baggie around the thermometer. Do not put the thermometer directly into the mixture as then it would not be safe to eat.

PART 2 (CreamIce Cream}:

  1. Fill the gallon-sized Ziploc bag about half to three-fourths full with ice.
  2. Add rock salt so that it is lightly coating the ice cubes, 2 tsp. is good. {Mix the ice and salt around}
  3. Take the initial temperature of the ice/ salt mixture by wrapping the baggie around the thermometer. Record on data table.
  4. Put the Ziploc sandwich bag with the ice cream mixture in it (keep it sealed!) into the gallon sized Ziploc bag—tuck it down into the ice so that it’s surrounded as much as possible.
  5. Seal the gallon sized bag with as much of the air out as possible.
  6. Wrap it in newspaper (insulator) and shake for 20-30 minutes really fast. It will be COLD! Read the Gathering Info section and start looking at the analysis questions. Take turns with your group members!

PART 3 (Gathering Creamy Data):

  1. Once your mixture is the correct consistency, use the thermometer to find the final temperature of the milk mixture (ice cream) and the rock salt/ice/water mixture by wrapping the baggies around the thermometer. Do not put the thermometer directly into the mixture as then it would not be safe to eat.{Record on data sheet!
  2. Once you have read the final temperatures, pour the contents of the gallon sized bag in the designated sink.
  3. {Dry off the ice cream bag as much as possible!} Take the final mass of the milk/ ice cream mixture.
  4. Get a plastic spoon, and enjoy your tasty thermal treat.
  5. Make sure your lab station is clean and all used bags are in the trash before you leave.

COLLECT YOUR DATA

Observations of Milk Mixture (Physical Description/State of Matter)

Before Shaking In Ice/Salt Mixture / During Shaking In Ice/Salt Mixture / After Shaking In Ice/Salt Mixture
INITIAL READINGS / FINAL READINGS / DIFFERENCE
Initial Mass of Milk Mixture / Final Mass of Milk Mixture
Initial Temp of Milk Mixture / Final Temp of Milk Mixture (Ice Cream)
Initial Temp of Ice/ Salt / Final Temp of Ice/ Salt

GATHER INFORMATION

It’s 35˚C in the shade and to cool off, you are eating an ice cream cone. As you sit there you wonder just how ice cream is made. One area of chemistry that helps to explain the making of ice cream is thermodynamics. There are three laws of thermodynamics:

0. If object 1 is in thermal equilibrium with two other objects, the other objects are in thermalequilibrium with each other. (Objects at Thermal Equilibrium are at the same temperature.)

1. The internal energy of a system can either be increased by adding heat or doing work.(Conservation of Energy.)

2. Heat will travel from hot to cold on its own and never from cold to hot. (Direction Heat Flows.)Using entropy: “In any natural process the entropy of a system increases OR the disorder of the system will increase.”

In making ice cream you remove about 1000 calories of heat from the milk/sugar (chocolate milk) mixture and transfer it to the salt/ice mixture. Energy is conserved and the first law is satisfied. Heat is always transferred from a hot object to a cooler one. Imagine your surprise if you had a glass of water and the water froze and the glass got hot. The 2nd law determines the direction of heat transfer and states heat always moves from a hot object to a cooler one.

Another aspect of chemistry involved is the properties of solutions as compared to pure solvents. The presence of solute (the thing being dissolved) particles in a solution will raise the boiling point and lower the freezing point of the solvent (the dissolver). Therefore, because the ice cream mixture is mainly a solution of sugar and water, its freezing point is depressed below 0˚ C.

Before refrigerators were invented, ice cream was made using ice. In this method, the “hot” ice cream mixture has to lose energy to the “cold” ice. Since ordinary ice is only 0˚ C, this is the lowest temperature that the ice cream could become. The ice cream mixture would still be a liquid.

To freeze the ice cream mixture, it is necessary to use “colder” ice. Again, properties of solutions provide the answers. A salt-ice mixture has a lower freezing point than pure ice, so it acts as “colder” ice. The more salt added to the ice, the lower the freezing point. The ice cream mixture can then lose more energy to the salt-ice mixture and freeze.

ANALYZE YOUR DATA

DISCUSSION QUESTIONS:

1. How would you define the second law of thermodynamics? How was it illustrated in this lab?

2. How does adding salt to ice make ice “colder”?

3. Was this lab showing a chemical or physical change that occurred? How do you know?

4. Why is the salt-ice mixture needed to freeze the ice cream mixture?

5. Explain why the ice cream mix freezes in terms of the transfer/flow of energy. Draw a diagram of the baggie-ice cream freezer. Use arrows to indicate the direction of the heat transfer and label the temperatures recorded for different systems.

6. How could you speed up the freezing of the ice cream mixture?

7. Graph the relationship of the temperature of the milk before shaking and after shaking it in rock salt freezer.

8. What did you find with your observations of the mass of the cream mixture in the bag? Was this an open or closed system? How do you know?

DRAW YOUR CONCLUSIONS

Write a DETAILED paragraph that includes the following:

  • Restate your scientific question and your hypothesis.
  • Tell whether your hypothesis was ACCEPTED or REJECTED by the data. Use actual data (qualitative and quantitative data) from your experiment to back it up.
  • Tell if you had anything go wrong/ unexpected in your experiment or if it went as you expected AND WHY. How did that affect your results?
  • How could you extend this experiment? How could you make it better, what would you change next time?

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