Lab 6: Cooling Curve
Name:
Group:
Minutes:
Grade:
Objective:_____________________________________________________________________________________
Introduction:
Substances are made of molecules, which can act as magnets and attract other molecules. The strength of
these attractions, called intermolecular attractive forces (IMAF), determines many of the physical properties that
substances exhibit. Among the most easily measured properties dependent on IMAF are the phase change
temperatures.
Equipment & Materials:
goggles
ring stand
test tube with substance
test tube clamp
Procedure: Obtain a test tube of the melted solid from the hot water bath on the hot plate under the fume hood. Bring
it back to your station, carrying it carefully with the included test tube holders. Clamp the test tube into place with the
test tube clamp and immediately begin timing. Record the temperature and phase (liquid, liquid + solid, solid) every 30
seconds in the “Temp” column. Continue this until the temperature reaches 30 oC.
Data Table
Time
(min)
Temp
(oC)
Phase
Time
(min)
Temp
(oC)
Phase
Time
(min)
Temp
(oC)
Phase
Time
(min)
0.0
6.5
13.0
19.5
0.5
7.0
13.5
20.0
1.0
7.5
14.0
20.5
1.5
8.0
14.5
21.0
2.0
8.5
15.0
21.5
2.5
9.0
15.5
22.0
3.0
9.5
16.0
22.5
3.5
10.0
16.5
23.0
4.0
10.5
17.0
23.5
4.5
11.0
17.5
24.0
5.0
11.5
18.0
24.5
5.5
12.0
18.5
25.0
6.0
12.5
19.0
25.5
Temp
(oC)
Phase
Analysis:
Part 1: Graph: A line graph will be used to analyze the data. You should use more than half of the graph
paper to complete the graph. Time is plotted on the X axis and Temperature on the Y axis. You will plot the
cooling data on the graph, starting at 0 minutes. Each data point point protector around it. Lines of best fit
will be drawn to represent the three line segments…substance as a liquid, substance as solid and substance
during the phase change. An example is given on the next page of how the graph should look when done.
The temperature where the slope is zero represents the phase change temperature. The middle line segment
(phase change) should have a ZERO slope…be perfectly level. Start the best fit line after the first steep slope
(this represents the glass in the test tube cooling, not the substance).
Example Of Graphing The Data
© 2011, Mark Rosengarten
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Label the graph with the following (check off as you do it):
Check
Job
1) Give the graph a title
2) On both axes, label what was plotted and the units
3) SOLID PHASE
4) LIQUID PHASE
5) LIQUID AND SOLID PHASE
6) FREEZING (put the temperature below)
What is the freezing point, based on the cooling curve?______________oC
Part 2: Identification of the Pure Substance
The list below contains substances that have many properties that are similar. Using the average phase change
temperature you determined above, identify the substance!
Substance
Capric Acid
Lauric Acid
Maleic Anhydride
Napthalene
Palmitic Acid
Paradichlorobenzene
Stearic Acid
Freezing Point
31 oC
44 oC
56 oC
81 oC
63 oC
53 oC
70oC
What is the identity of the pure substance?_________________________________________________
Calculate your percent error, using the temperature on the chart above as the accepted value and your
freezing point determined by the graph as the experimental value:
© 2011, Mark Rosengarten
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Questions:
Using the introduction for this lab, your notes and your brain, complete all of the following statements. Two lines
means two words in the answer. The statements are in chronological order.
1 The mystery pure substance started out as a
_________.
2 Since the temperature was decreasing, the
__________ energy was also increasing.
3 When there was very little change in the temperature, I
knew a _____ ______ was occurring.
4 The mystery pure substance was at its _________
__________.
5 Now, the ________________ energy was decreasing.
6 The temperature began to change again, when the
_________ phase was the only phase present.
7 The intermolecular attractive forces were now
_________ than they were in the beginning of the
experiment.
8 Since every substance has a unique freezing/melting
point, I looked on the chart and determined the
substance to be___________.
9 The temperature where the phase change occurred is
also the ______ ______ of the substance when heat is
added to turn the solid into a liquid.
Attach the graph that you drew and labeled to this page.
© 2011, Mark Rosengarten
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