Freezing point of Napthalene

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  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


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.