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        Temperature

Initial (0:00)          100oC                         7:00        78.5oC

0:30              97.5oC                              7:15        78.3oC

1:00              93.0oC                              7:30        78.3oC

1:30              89.5oC                              7:45        79.0oC

2:00              86.1oC                              8:00        79.0oC

2:30              84.6oC                              8:15        79.0oC

2:45              82.3oC                              8:30        79.0oC

3:00              81.2oC                              8:45        79.0oC

3:15              81.0oC                              9:00        79.0oC

3:30              80.5oC                              9:15        78.5oC

3:45              80.2oC                              9:30        78.1oC

4:00              80.0oC                              9:45        78.0oC

4:15              79.9oC                              10:00       78.0oC

4:30              79.8oC                              10:15       77.5oC

4:45              79.4oC                              10:30       77.0oC

5:00              79.1oC                              10:45       76.5oC

5:15              79.1oC                              11:00       76.0oC

5:30              79.0oC                              11:15       75.2oC

5:45              78.9oC                              11:30       73.8oC

6:00              78.8oC                              11:45       73.0oC

6:25              78.8oC                              12:00       72.1oC

6:30              78.7oC                              12:15       71.1oC

6:45              78.6oC                              12:30       70.3oC

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 acquired in this lab was minimal and easily explained.


Leave a Reply

Your email address will not be published. Required fields are marked *

Post comment