Phase Change Lab
Name____________________________Period___________
Do this again! READ 17.3 /ADD to your 17.3 notes
Learning Goals
I can..
describe the phases of matter and explain qualitatively and quantitatively how energy flow affects
changes in phase/state.
discuss heat transfer and temperature changes on the cooling/heating curve for the phase changes of
water, paraffin wax, or lauric acid.
perform a phase change experiment demonstrating the different phase changes of water, paraffin was, or
lauric acid.
Research Question:
How can you use a warming/cooling curve to determine a substance's melting and/or freezing point?
Materials
Ring stand
Clamp
large beaker
Test tube holder
Tap water
Paraffin wax
SPARK with temperature probe for wax temp
“Extra” thermometer for water temp
***Safety Goggles Should be Worn At All Times***
Procedure:
1. Begin by obtaining all necessary materials.
2. In a beaker, warm some tap water to 60° - 65°C using a hot plate. Place the “extra” thermometer into the water bath.
3. Once the water bath is up to temperature, immerse the solid paraffin into the water bath.
4. Wait for the wax to melt completely. It may be necessary to re-heat your water if melting slows.
5. Place the SPARK thermometer into the melted wax. Move the test tube to a beaker with room temp or slightly cooler
water (cool tap water is OK).
6. IMMEDIATELY begin collecting data. Record the temperature of the PARAFFIN every 30 seconds.
7. Record your data for 8-12 minutes, or until the wax is more-or-less completely solidified.
IMPORTANT: As the wax solidifies, make sure its thermometer is in the center of the test tube,
NOT TOUCHING the sides or BOTTOM!!! Your temperature probe should now be stuck in the wax.
The data you just collected should be recorded in the COOLING CURVE table.
8. Repeat the experiment to obtain a WARMING CURVE set of data. To do this, place the solid wax into the hot water
bath and record your temperatures until the wax is more-or-less completely melted.
9. When finished, allow your wax to re-solidify at room temperature. Clean off the thermometer...use warm water and a
paper towel to remove any residual wax.
10. Clean up your lab table and wash your hands.
Cooling Curve Data:
TIME
TEMPERATURE
TIME
TEMPERATURE
TIME
TEMPERATURE
9. When finished, allow your wax to re-solidify at room temperature. Clean off the thermometer...use warm water and a
paper towel to remove any residual wax.
10. Clean up your lab table and wash your hands.
Cooling Curve Data:
TIME
TEMPERATURE
0
30
60
90
120
150
180
210
240
Warming Curve Data:
TIME
TEMPERATURE
0
30
60
90
120
150
180
210
240
TIME
270
300
330
360
390
420
450
480
TEMPERATURE
TIME
540
570
600
630
660
690
720
750
510
TIME
270
300
330
360
390
420
450
480
510
TEMPERATURE
780
TEMPERATURE
TIME
540
570
600
630
660
690
720
750
780
TEMPERATURE
Conclusion & Reflection:
1. Using an Excel spreadsheet, create a line graph showing the temperature vs. time of the paraffin wax warming AND
cooling, using the data you collected.
2. Compare the warming curve of the paraffin with that of the cooling curve. What is the general “trend” of the graphs yo
made?
3. What effect would increasing amount of wax have of the shape of the curve?
BIG IDEAS…
4. From the data collected, what is the melting point of paraffin wax? What is the freezing point?
5. Why does the graph look like it does? What do the "flat" areas on your cooling/warming curves represent?
Do the following to complete a phase change graph for water:
1. Make 100mL ice water slurry in a 250mL beaker.(This should be mostly ice, with enough water to fill
the spaces.)
2. When the temperature has stabilized record the temperature. This will be time zero
3. Place your beaker on a hotplate or over a Bunsen burner and record the temperature about every 30 seconds. (Fill in
data table bleow) Finish the time column
4. BE SURE TO STIR BEFORE MEASURING THE TEMPERATURE! Your thermometer MUST NOT touch the sides
or bottom of the beaker.
5. Allow your water to come to a boil.
TIME
TEMPERATURE
0
30
60
90
120
150
180
210
240
270
300
330
360
390
420
450
480
510
TIME
540
570
600
630
660
690
720
750
TEMPERATURE
TIME
780
Post Lab Questions:
1. Explain what happens when heat is absorbed (endothermic)?
2. Explain what happens when heat is released (exothermic)?
3.Why are the melting point and freezing point of a substance always the same?
TEMPERATURE
4.Why is there a plateau in a heating curve as a substance changes state? (where does the energy go?)
5. Sketch the shape of a cooling curve as a substance goes from a gas to a liquid to a solid.
6. What was the first phase change called?
a. What two phases of water were present during the first phase change?
b. What was the temperature range during the first phase change?
7. What was the second phase change called?
a. What two phases of water were present during the second phase change?
b. What was the temperature range during the second phase change?
8. Mark the area of the graph during which the water was NOT undergoing a phase change.
a. What phase of water was present during this period of time?
b. What was the temperature range during this period of time?
8. Compare the temperature ranges of the three areas of the graph.
What happens to temperature during the phase changes of water?
9. Are boiling point and melting point intensive properties of a substance, or extensive properties?
10. What if one group of students misread the lab directions and made a 1000mL ice water slurry instead
of
100mL.
a. What affect would this have on the amount of time it takes to boil the water?
b. What affect would this have on the temperature at which the water boiled?
11. Are melting and boiling exothermic, or endothermic processes? Explain
12. Is the kinetic energy of the water molecules increasing or decreasing during the lab?
13. If we reversed the process of the lab, we would take water vapor and change it to liquid water.
a. What is this phase change called?
b. At what temperature would the gas to liquid phase change happen?
c. Is it an exothermic or endothermic process?
14. If we continued to reverse the process of the lab, we would take liquid water and change it to solid
water.
a. What is this phase change called?
b. At what temperature would the liquid to solid phase change happen?
c. Is it an exothermic or endothermic process?
15. Would kinetic energy increase or decrease during the reverse process?
16.Unless a substance is at absolute zero (zero on the Kelvin scale), it has kinetic energy, and thus the
particles are moving.
a. What type of motion do particles within a solid have?
b. What types of motion do particles within a liquid have?
c. What types of motion do particles within a gas have?
17. Identify heat of fusion on your graph. Explain heat of fusion.
18. Identify heat of vaporization on your graph. Explain heat of vaporization.
Lauric Acid Lab Directions:
http://teacherweb.com/NY/SpackenkillHighSchool/jlatino/Lab6HeatingandCoolingCurves.pdf
Heat of Vaporization and Heat of Fusion Calculations:
http://www.kentchemistry.com/links/Energy/ComplexCalProblems.htm