Changing Phase
Spotting phase changes in the test tube


In the window above, you see a test tube containing ice. You can heat the test tube and its contents by clicking on the Bunsen burner, and cool the test tube and contents by clicking on the dry ice bucket. There is a thermometer sticking out of the test tube, which measures the temperature of the molecules inside.

Slowly heat the test tube to a maximum temperature by clicking on the Bunsen burner until it no longer functions. Then cool the test tube down to its minimum temperature. While heating and cooling the test tube watch carefully for signs of phase change.

Then please answer the question below and submit your answer for anonymous sharing with your teacher and classmates.




Which of the following phase changes did you observe? Check ALL that apply:

a. freezing b. melting c. sublimation d. deposition e. boiling f. condensing
Noticing temperature during phase change


Try heating and cooling the test tube again and watch the thermometer carefully.



Describe what happens to the thermometer when the water is going through a phase change.

Thermometer results
Some of your classmates' answers should appear below when your teacher selects them for display. If they aren't visible yet, move on to the next step and check back later for results or look at the results on the projector's screen.

Question




Your thermometer results


Do you think that any of the answers on this page are incorrect? Why or why not?
Taking a snapshot of liquid water






To the right of the test tube image you now see a molecular level model of water molecules at the temperature that is currently inside the test tube. The molecules are colored according to the kinetic energy they have. (Recall that kinetic energy is the energy an object possesses due to its motion.) In the model, high kinetic energy = red, and low kinetic energy = white.

Heat the ice until you have a liquid, and take a shapshot of the model in the liquid state.

In the snapshot's notes section, located at the bottom of your lab notebook window, describe why you think your shapshot represents liquid water.




Insert your snapshot and description of liquid water:
Liquid water results
Some of your classmates' answers should appear below when your teacher selects them for display. If they aren't visible yet, move on to the next step and check back later for results or look for the results on the projector's screen.

Question



Your liquid water results


Choose one picture that you think is correct, and one that is incorrect, and explain why you believe this is so for each one. (Identify the pictures by their number.)
Finding another phase change



Take a snapshot of one other phase change, and describe how you know the model is showing water going through a phase change. Talk about what you see in the test tube, what you see in the model, and what the thermometer is doing.


In the snapshot's notes section, located at the bottom of your lab notebook window, describe what you see in the test tube, what you see in the model, and what the thermometer is doing.





Insert your phase change snapshot and description:
Predicting a heating/cooling curve

Every time you click on the Bunsen burner you add to the total energy of the test tube and water. Every time you click on the dry ice you decrease the total energy of the test tube and water. If you were to graph temperature vs. total energy, what do you predict the graph would look like?





Heating/cooling predictions
Some of your classmates' predictions should appear below when your teacher selects them for display. If they aren't visible yet, move on to the next step and check back later for results or look for the results on the projector's screen.

Question




Your predictions

Why do you think these predictions look so different?
Making a heating/cooling curve



Heat the ice in the test tube until it turns to steam. The temperature vs total energy graph will automatically be plotted for you.

Prediction


Plateaus

Energy


How was your prediction similar or different from what actually occurred on the temperature vs total energy graph? What do the plateaus (stage II and IV) in the graph correspond to? In other words, what is happening with the water when the graph stays flat? During these plateaus, the total energy is changing (due to application of the flame or dry ice) but the temperature stays constant. Why does that happen? Where is the energy going to or coming from if the temperature doesn't change?
Prediction results


Plateau results

Question




Your plateau results


After looking at other answers, what do you think is happening with the water when the graph stays flat?
Energy results