SOTM LAB: C2

I. TEACHER'S NOTES AND GUIDELINES

TITLE OF LAB: Phase Change

DEVELOPERS OF LAB: A. De Cheke, J. Guadagno(JD524), T.Kiszkiel(JD851), R. Okraski(JD590), B. Riemer(JD819), J. Shillieto, J. Stoutenburgh(JD803), M.J. Tumer(JD587), L. Weisberg(JD591), R. Weiss; Kathy Poncelet(JD521), Pamela Iacovella (JD723), Mikki Bieber (JD705), SOTM staff

OVERVIEW:DESCRIPTIONThis lab is designed to enhance the student's understanding of phase changes of a substance and relate how energy changes and temperature variations accompany these changes of state. After seeing an example of the heating curve of water, students will be asked to use inquiry to identify other substances based on their freezing/melting point.

CURRICULUM CONSIDERATIONSThis would be appropriate when covering curriculum involving physical changes, energy transfers, and reading and interpreting their relationships using graphs. It is important for the student to be able to distinguish between melting and freezing; energy and temperature; and endothermic and exothermic changes. The purpose of this lab is to have students create a graph involving phase changes of a substance so they can clarify and explain the above concepts.

SAFETY CONSIDERATIONSUse goggles at all times in the laboratory.Keep all leads from probes, the probes, and sensors away from direct heat sources to avoid

damage to equipment.If using p-dichlorobeneze, or another hazardous chemicals, follow the precautions stated on

the Material Safety Data Sheet.Dispose of all chemicals as directed by your teacher.Make sure to wash your hands before leaving the lab

BACKGROUND INFORMATION:A SCIENTIFIC VIEWPOINTThe freezing point, the temperature at which a pure substance turns from a liquid to solid, and melting point, the temperature at which a pure substance turns from a solid to liquid, are characteristic of physical properties. The following concepts will be investigated in this experiment: phase changes occur at constant temperatures, melting is an endothermic process, freezing is an exothermic process, and both melting and freezing occur at the same temperature.

COMMON MISCONCEPTIONS:1. Melting and freezing occur at different temperatures.2. Boiling and condensation occur at different temperatures.3. During a change in phase, the temperature changes.4. Boiling can only occur at 100 'C.5. As you add heat, the temperature will always increase.

1

6. Heat is measured by temperature.7. Phase changes result in a chemical change in the substance.

OBJECTIVES:To study the effects of heating and cooling a pure substance through a change of phase.To construct heating and cooling curves of a pure substance using experimental data.To determine the freezing and melting point temperatures of a pure substances.To differentiate between temperature and heat.To interpret a graph generated from lab measurements.To unknown substances on the basis of their melting point and other physical properties

EQUIPMENT/MATERIALSPROVIDED BY SOTMLaptop Pasco InterfaceTemperature SensorHot plate p-Dichlorobeneze or lauric acid (approximately 20 g or 1/2 filled test tube)

PROVIDED LOCALLYRing stand with test tube clampTest tubes (2)Test tube standSpatula400 mL beaker

# For inquiry, students may need paraffin, chocolate, magic shell, fats. Etc.

ADVANCE PREPARATION:Set out required equipment and materials.Have available possible unknowns for students to investigate

II. PRE-LABSUGGESTED PRE-LAB EXERCISES FOR ELICITING STUDENTS PRIOR KNOWLEDGE AND MISCONCEPTIONS:

1. Create a concept map using the following vocabulary words: freezing point, kinetic energy, potential energy, thermometer, temperature, solid, liquid, phase change

2. Interview two friends or relatives using this question: why does freezing occur?a. Record their answers.b. Look up the correct answers.c. Compare the correct concept with their answers by explaining the differences

between each.3. Have students make a drawing comparing the three phases of matter, showing the

comparisons of motion, bonding, and spaces between molecules. 4. Administer assumption pre-test exercise to students.5. Preview answers to pre-test and discuss misconceptions with students prior to lab.

2

III. EXPLORATION OF SCIENTIFIC PRINCIPLE & INTRODUCTION OF EXPERIMENTAL PROTOCOLPURPOSE:The purpose of this lab is to learn to use the temperature probe in the Pasco Science Workshop to determine the freezing and melting point of a pure substance, create a table and graph of data, and interpret the results. When this part of the investigation is complete, the students will use what they have learned to do further inquiry into questions that might have arisen through this lab, or to investigate other unknown substances.

LAB PROCEDURES:1. Plug in AC adapter into back of computer.2. Plug in PASCO interface into computer3. Plug in the interface power cord.4. Plug in the temperature probe.5. Turn on interface then turn on the computer.6. Double click on the Science Workshop icon with the mouse.7. When the Science Workshop program is loaded, click and hold on the analog plug icon and

drag to it to position "A" on interface.8. Choose "temperature sensor" using mouse and double click on temperature sensor.9. Click and hold on graph icon and drag to position "A" on interface.

10. Move the graph display by clicking on the title bar and dragging the graph display to the lower part of screen.

11. Click and hold on the table icon and drag it to position "A" on interface. Move the table to lower part of the screen by clicking on the title bar and dragging to lower part of screen.

12. Double click on sampling option.a. Select none for "Start" and "Stop" conditions by clicking on "none" with mouse.b. Under periodic sample select 15 secondsc. Click on okay.

13. Reduce interface screen by clicking on middle box in title bar.14. Drag the graph display to the center of the screen. Refer to procedure #10 for dragging

instructions.15. Drag table to center of screen in a similar manner.16. Testing the operation of probe.

a. Double click on the "Rec" button.b. Observe the graph and table to see if readings are being recorded.c. Record for 30 seconds.d. Click on the "Stop" button.

17. Investigating the graph display function keys.a. Expand the graph to see entire graph by double clicking on the graph title barb. Expand one portion of graph by clicking on the magnifying glass icon and moving

the magnifying glass on to the graph. Click on top/left of the area you want to examine and drag the mouse to the opposite bottom comer of the area you want to examine.

c. Return the graph to full size by following step A.d. Locate an exact point on the graph by clicking on the cross hair icon and moving it

to the desired location on the graph. Read and record the "x" and "y" coordinates.e. To clear the graph, highlight run #1 under DATA with the mouse and press the

Delete key.

3

18. Prepare a hot water bath, using a 400 mL beaker half full of water and heat on a hot plate to a temperature of about 70o C. (The temperature of the water bath can be monitored by putting the temperature probe in the water and clicking on the “Mon” button.)

19. Heat the test tube with the sample to be investigated by placing it in the hot water bath.20. When the sample is completely melted, remove it from the water bath.21. Insert the probe making sure that the probe is in the middle, of the sample, not touching the

test tube or the results may be inaccurate.22. Click on "Rec".24. While the sample is cooling, observe any changes that take place in the sample.23. When the temperature reaches 40°C, click on "Stop".24. Replace the sample in the hot water bath and slowly heat the sample back up to 70°C25. Record the temperature as the sample is heated26. Investigate the graphs using the display function keys (refer to step 17).

a. Click on data.b. Highlight runs 1 & 2 so both have check marks.c. Expand entire graph (step 17d. Expand and view the region where the heating and cooling graphs coincide (step

17b)27. Record the temperature and times at which the heating and cooling curves cross (step 17d).28. Save the data.

a. Insert a disc into drive A.b. Highlight the table by clicking on the title bar.c. Display the data from both runs by dragging the table icon to channel A, then click

on temperature probe.d. Click on “Data” on the first table, click on Run #1.e. Click on “Data” on the second table, click on Run #2.f. Click on file in the upper left comer of screeng. Check on export active display.h. Click drive and select drive "A" by double clicking.i. Click on file name.j. Double click in file name box and type the name of the file (no more than 8

characters).k. Click on OK.

29. Shut down the computer.a. Click on file in upper left-hand comer.b. Double click on quit.c. Click on start in bottom left comer of screen.d. Click on shutdown.e. Answer "yes". The computer will shut itself off.

30. Clean-up the lab area and put supplies away.32 Print the graph.

4

POST LAB DISCUSSION QUESTIONS1. Define and explain the terms: heat of fusion and heat of vaporization.Correct response: Heat of fusion is the amount of heat energy absorbed per gram of substance

in melting or the amount of heat energy released per gram of substance in freezing at a constant temperature. Heat of vaporization is the amount of heat energy absorbed per gram of substance in boiling or the amount of heat energy released per gram of substance in condensing at a constant temperature.

2. How do these terms relate to the lab?Correct Response: The heat of fusion is the point on the graphs where there is no change in

temperature- the flat region. The same idea is true for phase changes at the boiling point.

3. Using a reference book, record the heat of fusion and the heat of vaporization for the substances used.

4. Do melting and freezing occur at approximately the same temperature? Support your answer using your observations and graph.

Correct Response: Yes, students should reference points on their graph where heating and cooling graphs coincide. Some students might have a slightly higher temp during melting than cooling, due to contamination, inconsistent heating or cooling, or location of the probe.

5. How is energy involved in phase changes?Correct Response: Energy is absorbed in melting and released in freezing at a constant

temperature.

6. Explain endothermic and exothermic changes.Correct Response: Endothermic change occurs when energy is absorbed. Exothermic change

occurs when energy is released.

7. Explain the difference between melting and freezing.Correct Response: The difference is in the direction of heat flow. Melting is endothermic and

freezing is exothermic.

8. Are heat and temperature the same thing? Explain.Correct Response: No, heat is a form of energy. Temperature is a measure of the average

kinetic energy of a substance.

9. Why does a drink get colder when you put an ice cube in it?Correct Response: Ice absorbs heat from the drink making the drink colder and melting the ice

cube.

5

IV. ELABORATION OF SCIENTIFIC PRINCIPLE: INQUIRY-BASED STUDENT INVESTIGATION

PROBLEM:Using what you have learned in the previous exercise, design an experiment to test a question that you have devised. Attempt to determine the identity of an unknown substance using the samples provided by your teacher and the known values of melting and freezing points of these substances.

HYPOTHESIS OR PREDICTIONUsing the information available, make a prediction of your results based on your experience

EXERIMENTAL DESIGNDesign an experiment to test your hypothesis, listing all materials to be used, safety considerations, and complete, reproducible, step by step instructions.

What is the control?What is the variable?How will you test your hypothesis?How will you collect and record the data?

6

Rubric for assessment of Student Inquiry Lab

Student’s Name___________________________

Student Activity Date of Completion Teachers InitialsStudents have proposed a questionStudents have proposed a hypothesisStudents have stated reason for predicted outcomeStudents have created procedureStudents have considered safety and viabilityStudents have identified controlsStudents have identified variablesStudents have created a material listStudents have successfully run procedureStudents have recorded data correctlyStudents have completed calculationsStudents have listed % error and sources of errorStudents have proposed ways to improve the procedureHave students tested their hypothesis?Are the student’s conclusions consistent with their dataAre student’s data, calculations and outcome logical and consistent with known scientific concepts?What new questions have arisen during this lab?

7

Student’s Name ______________________

PLAN FOR DATA COLLECTION & ANALYSIS

Checkpoint (Teacher checks students’ plan for feasibility.)

CONDUCTING THE EXPERIMENT

Checkpoint (Teacher monitors students’ investigations in progress.

ANALYSIS OF DATA

Checkpoint (Teacher checks students’ analysis.)DISCUSSION OF RESULTS

COMPARE

PERSUADE

RELATE

8

ASSUMPTION PRE-TEST

1. Which of the following graphs shows a solid undergoing a phase change from solid to liquid?

2. Which set of diagrams reflects the boiling point of different substances?

3. Which graph shows the melting of a solid with the absorption of heat?

4. Is energy involved as a substance melts? Explain.

5. Do different phases of the same substance have different chemical properties? Explain.

6. Does melting and freezing occur at the same temperature? Explain.

9

V. EVALUATIONPOST LAB DISCUSSION QUESTIONS PHASE CHANGE LAB

1 Define and explain the terms heat of fusion and beat of vaporization.

2. How do these forms relate to the lab?

3. Using a reference book, record the heat of fusion and the heat of vaporization for the substances used.

4. Do melting and freezing occur at approximately the same temperature? Support your answer using your observations and graph.

5. How is energy involved in phase changes?

6. Explain endothermic and exothermic changes.

7. Explain the difference between melting and freezing.

8. Are heat and temperature the same thing? Explain.

9. Why does a drink get colder when you put an ice cube in it?ALTERNATIVE

Write a story of Joe/Josie the molecule and trace their existence through the three phases of matter.

10

This may be done in the form of a cartoon, written story, or advertisement.

SCORING RUBRICDoes the student illustrate knowledge of the following concepts?

Phase changeEnergy transferTypes of energySpatial relationships between molecules in the three phasesEndothermic and exothermic reactions

Does the student use appropriate examples in their representation?

Is it clearly written and presented well?

This material is based upon work supported by the National Science Foundation under Grant No. ESI 9618936. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

11