Freezing Point of Naphthalene

I. Purpose

To determine the freezing point of a known substance, naphthalene

II. Materials

ringstand gas source
test tube test tube clamps
thermometer naphthalene
Bunsen burner goggles
hose stopwatch

III. Procedure

1. Assemble the Bunsen burner, attaching one end of the hose to the
burner and the
other to a gas source.
2. Assemble the ring stand so that a ring clamp is attached to the
stand holding the
test tube that will be used in the experiment.
3. Fill the test tube to approximately 1/8 capacity with
naphthalene crystals.
4. Place the thermometer in the crystals so that it is surrounded
by the naphthalene
powder but not touching the sides or bottom of the test tube.
Use a clamp to hold
the thermometer in place.
5. Ignite the Bunsen burner and using direct heat melt the
naphthalene powder until
it completely turns to a liquid. When the temperature reaches
approximately 90o
Celsius, stop heating.
6. Observe the change in temperature from 90o to 70o Celsius,
recording the
temperature at regular intervals, preferably 15 seconds. This
data will be used to
make a chart later.
7. Once the temperature has fallen to 70o, melt the naphthalene
which is now
frozen to remove the thermometer. Properly dispose of
the naphthalene liquid as
instructed by the teacher.

IV. Data

Time Elapsed Temperature of Naphthalene Time

Initial (0:00) 100oC 7:00
0:30 97.5oC 7:15
1:00 93.0oC 7:30
1:30 89.5oC 7:45
2:00 86.1oC 8:00
2:30 84.6oC 8:15
2:45 82.3oC 8:30
3:00 81.2oC 8:45
3:15 81.0oC 9:00
3:30 80.5oC 9:15
3:45 80.2oC 9:30
4:00 80.0oC 9:45
4:15 79.9oC 10:00
4:30 79.8oC 10:15
4:45 79.4oC 10:30
5:00 79.1oC 10:45
5:15 79.1oC 11:00
5:30 79.0oC 11:15
5:45 78.9oC 11:30
6:00 78.8oC 11:45
6:25 78.8oC 12:00
6:30 78.7oC 12:15
6:45 78.6oC 12:30

V. Graph

(See following pages)

VI. Calculations

Using 80.1 oC as the theoretical value for the freezing point of
naphthalene, we can now
determine percent error.

Percent Error = ((Theoretical - Experimental) / Theoretical) x 100
Percent Error = ((80.1 oC - 79.0 oC) / 80.1oC) x 100
Percent Error = 1.4%

VII. Conclusions

In this lab, we heated the known substance naphthalene in a test tube to
approximately 100oC and observed its temperature while it cooled to
approximately 70oC. Over a time period of 12 minutes and 30 seconds, we recorded
the temperature at regular 15 second intervals, and, with this data, constructed
a chart showing the general curve. Upon inspection of the graph and our data
chart, we found the experimental freezing point of naphthalene to be around 79oC.
This results in 1.4% error when compared to the actual value for the freezing
point of naphthalene, 80.1oC. Considering the impurities in the consumer grade
naphthalene, the interference of outside air on the temperature of the test tube
and its contents, and the inaccuracy of 1/10 measurements on a thermometer
graduated by whole numbers, the error we accquired in this lab was minimal and
easily explained.

Category: Science