Heating and Cooling Curves
Paris Thatos
Partner: Alan Delaney
Partner: Mikey Christopher
Due 10/26/09
PreLab:
The transfer of heat is indicated by measuring its effect on the temperature
of the surroundings (one example being the water in a calorimeter). No direct
measurements of the substance undergoing the heat transfer are made. IN this
experiment, we will observe, by direct measurement, the effects of heating and
cooling a pure substance.
Purpose:
To study the effects of heating and cooling a pure substance through change of
phase. To also construct heating and cooling curves based on observational data.
And to determine the freezing and melting point of the substance.
Materials:
Refer to lab pages 89 – 90 for materials and equipment.
One change in the equipment was used: lauric acid was substituted out for steric
acid.
Safety:
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Do not come into contact with or inhale vapors of the steric acid. Avoid
consumption
Tie back long hair and loose clothing when using the Bunsen burner.
Heat safety goggles in the laboratory.
If using a mercury thermometer, take caution. The mercury is highly
poisonous and can be deadly if the thermometer breaks.
Procedure:
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Obtain a test tube of steric acid and use a beaker of water to construct a hot
water bath.
Once the steric acid has fully melted, put a thermometer into the acid and
begin keeping track of the time.
Record the temperature every 30 seconds until the emperature drops to 45
degrees Celsius.
If there is adequate time, remove from source of heat and begin taking
measurements every 30 seconds until the temperature reaches 80 degrees
Celsius
Observations:
Time (minute)
Temp (degrees Celsius)
0
83
0.5
78
1
74
1.5
68
2
65
2.5
64
3
62
3.5
60
4
59
4.5
57
5
56
5.5
54
6
53
6.5
53
7
53
7.5
53
8
53
8.5
53
9
53
9.5
53
10
53
10.5
53
11
53
11.5
53
12
53
12.5
53
13
53
13.5
53
14
53
14.5
53
15
53
15.5
53
16
53
16.5
53
17
53
17.5
53
18
53
18.5
52
19
52
19.5
52
20
51
20.5
51
21
51
21.5
51
22
51
22.5
50
23
50
23.5
50
24
49
24.5
49
25
49
25.5
48
26
47
26.5
47
27
46
27.5
45
Calculations:
Construct a cooling curve with the data:
Inadequate time to run experiment needed to construct heating curve
Questions:
1. Referring to your graph, determine the freezing point of steric acid. How
does this temperature compare with the melting point of the same substance
as indicated by your graph?
The freezing point of steric acid is 53 degrees Celsius. There was inadequate
time to complete the heating curve, but the melting point would be the same
temperature.
2. Explain the diagonal parts of the cooling curve in terms of changes in kinetic
and potential energy
The diagonal parts of the graph are the times where kinetic energy and the
potential energy of the substance change.
3. What phase changes are exothermic? Endothermic?
The endothermic phase changes are melting and boiling. The exothermic
phase changes are freezing and condensing.
4. In which phase of a substance do the particles have the greatest amount of
kinetic energy.
The phase of a substance where the molecules have the greatest amount of
kinetic energy is the gas phase.
Conclusions:
Heating and cooling curves can be used to accurately tell us important
information about certain substances. We can use them to tell the melting points
and boiling points of many pure substances. That, and the fact that they can be easily
constructed; make heating and cooling curves an important aspect of chemistry.