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Name ___________________________
Chapter 17 •
34
Date ___________________
Class __________________
Thermochemistry
EXPERIMENT
THE SPECIFIC HEAT OF A METAL
PURPOSE
To determine the specific heat of a substance.
Text Reference
Sections 17.1 and 17.2
Time Required
40 minutes
Objectives
• Measure the specific heat
of lead.
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• Identify an unknown metal
from its specific heat
(optional).
Advance Preparation
Unknown metal samples
Use 1-cm diameter rods of
aluminum, brass, copper,
zinc, and stainless steel. Saw
them into lengths between
2 cm and 5 cm.
Students may wish to cut
some cardboard lids for their
cups. There should be holes
in the lids to accommodate
the stirring rods and
thermometers.
BACKGROUND
On a sunny day, the water in a swimming pool may warm up a degree or
two while the concrete around the pool may become too hot to walk on
in your bare feet. This may seem strange because both the concrete and
the water are being heated by the same source—the sun. This evidence
suggests it takes more heat to raise the temperature of some substances
than others. This, in fact, is true: The amount of heat that is required to
raise the temperature of 1 g of a substance by 1C is the called the specific
heat capacity, or simply the specific heat, of that substance. Water, for
example, has a specific heat of 1.0 cal/(gC). This value is high in
comparison with the specific heats for other materials, such as concrete.
In this experiment, you will use a simple calorimeter and your
knowledge of the specific heat of water to determine the specific heat of
lead.
MATERIALS (PER PAIR)
safety goggles
400-mL beaker
ring stand
ring support
wire gauze
gas burner
50-mL beaker
centigram balance
large test tube
utility clamp
100-mL graduated cylinder
plastic-foam cup
250-mL beaker
thermometer
glass stirring rod
lead shot, Pb t
distilled water
unknown metal t
SAFETY FIRST!
In this lab, observe all precautions, especially the ones listed below. If
you see a safety icon beside a step in the Procedure, refer to the list below
for its meaning.
Caution: Wear your safety goggles. (All steps.)
Caution: Lead is a toxic metal. Wash your hands thoroughly
after use. (Step 2.)
Caution: Do not touch hot equipment. (Steps 1, 3, 6.)
Experiment 34 The Specific Heat of a Metal 211
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Date ___________________
Class __________________
Caution: If you should break a thermometer, immediately
report the incident to your teacher. Never use a thermometer
as a stirrer. (Step 6.)
Note: Return or dispose of all materials according to the
instructions of your teacher. (Step 7.)
PROCEDURE
As you perform the experiment, record your data in Data Table 1.
1. Heat 250 mL of water in a 400-mL beaker until it is boiling
gently.
2. While the water is heating, determine and record the mass of a
clean, dry 50-mL beaker to the nearest 0.01 g. Add between
80 g and 120 g of lead shot to the beaker. Measure the
combined mass of the beaker and lead to the nearest 0.01 g and
record the measurement.
3. Transfer the lead shot to a large, dry test tube. Use the utility
clamp to suspend the test tube in the boiling water, as shown
in Figure 34.1. The lead shot should be below the level of the
water in the beaker. Leave the test tube in the boiling water
bath for at least 10 minutes.
Large test tube
Ring stand
400-mL beaker
Metal
Wire gauze
Ring support
Figure 34.1
212 Chemistry Laboratory Manual
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Utility clamp
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Date ___________________
Class __________________
Plastic-foam cup
250-mL beaker
100 g water
Figure 34.2
4. While the lead shot is heating, measure 100 mL of distilled
water in a graduated cylinder. Pour the water into a plasticfoam cup and place the cup in a 250-mL beaker for support, as
shown in Figure 34.2.
5. Measure and record the temperature of the water in the plasticfoam cup and of the water in the boiling bath.
6. Remove the test tube from the boiling water and quickly pour
the lead shot into the water-filled, plastic-foam cup. Place a
thermometer and a glass stirring rod into the cup. Use the
stirring rod to gently stir the lead shot. Do not stir the lead shot
with the thermometer. Note the temperature frequently and
record the maximum temperature reached.
Step 7.
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The lead shot can be toweldried initially and then airdried between classes.
7. Pour the water off and return the lead shot to your teacher.
8. (Optional) Follow the same procedure to determine the
specific heat of an unknown metal.
Experiment 34 The Specific Heat of a Metal 213
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Date ___________________
Class __________________
OBSERVATIONS
DATA TABLE 1: MEASUREMENTS OF MASS AND TEMPERATURE
Trial 1
mass of 50-mL beaker
Trial 2
32.14 g
32.16 g
mass of 50-mL beaker lead shot
142.76 g
138.24 g
mass of lead shot
110.62 g
106.08 g
initial temperature of water in cup
23.00C
23.20C
initial temperature of lead shot
(temperature of boiling water)
99.02C
99.24C
maximum temperature of lead water
25.54C
25.47C
mass of water
100 g
100 g
ANALYSES AND CONCLUSIONS
1. Determine the changes in temperature of the water (Twater) and of the lead shot
(Tlead) for each trial.
trial 1
trial 2
2. Calculate the heat gained by the water in each trial.
trial 1
trial 2
qwater¬ mwater cwater Twater
¬ 100 g 1.00 cal/(gC) 2.54C
¬ 254 cal
qwater¬ mwater cwater Twater
¬ 100 g 1.00 cal/(gC) 2.27C
¬ 227 cal
214 Chemistry Laboratory Manual
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Twater¬ 25.54C 23.00C 2.54C
Tlead¬ 25.54C 99.02C 73.48C
Twater¬ 25.47C 23.20C 2.27C
Tlead¬ 25.47C 99.24C 73.77C
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3. Remembering that the heat gained by the water is equal to, but has the opposite
sign of, the heat lost by the lead, calculate the specific heat of lead for each trial.
trial 1
qlead¬ qwater mlead clead Tlead
254 cal
qwater
clead¬ 110
.
62
g
(73.48C)
mlead Tlead
¬ 0.0312 cal/(gC)
trial 2
qlead¬ qwater mlead clead Tlead
227 cal
qwater
clead¬ 106.08 g (73.77C)
mlead Tlead
¬ 0.0290 cal/(gC)
4. Calculate the average value for the specific heat of lead in your experiment.
trial 1 value trial 2 value
average¬ 2
0.0312 0.0290
¬ 2
¬ 0.0301 cal/(gC)
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5. If you tested an unknown, repeat these calculations to determine the specific heat
of the unknown metal.
6. Calculate the percent error in the specific heat value that you determined
experimentally. Use the accepted value given by your teacher.
|experimental value accepted value|
percent error 100%
accepted value
The accepted value for the specific heat of lead is 0.0306 cal/(gC).
|0.0301 cal/(gC) 0.0306 cal/(gC)|
percent error¬ 100%
0.0306 cal/(gC)
0.0005 cal/(gC)
¬ 100%
0.0306 cal/(gC)
¬ 1.63%
¬ 2% (one significant figure)
Experiment 34 The Specific Heat of a Metal 215
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Date ___________________
Class __________________
7. You assumed that the initial temperature of the lead shot was the same as that of
the boiling water. If the lead shot was actually at a lower temperature than the
water, how would your value for the specific heat be affected?
The value calculated for the specific heat of lead would be low.
8. Identify other possible sources of error in this experiment.
Errors could be introduced in taking the temperatures and in measuring the mass
of the lead shot.
9. Compare your value for the specific heat of lead to the values obtained by your
classmates. Can specific heat be used to identify substances? Explain.
Yes. It is a value that is constant for the same substance under different conditions,
and that varies for the different substances under identical conditions.
GOING FURTHER
Develop a Hypothesis
Design an Experiment
Propose an experiment to test your hypothesis. If resources are available and you
have your teacher’s permission, perform the experiment.
216 Chemistry Laboratory Manual
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Based on the results of this lab, develop a hypothesis about how the measured
specific heat of lead would differ if the hot lead was added to water in vessels made
of different materials.