Freezing Point of Naphthalene

 Freezing Point of Naphthalene

Purpose: 

complete with the correspondent purpose

Materials

List the materials using bullets.

Procedure

1. Assemble the lab setup as in the picture.
2. Build a data table
3. Fill the test tube to approximately 2 cm high 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. Turn on your heat source (Bunsen burner or Hot plate)
6. Place the test tube inside the water bath and begin heating until the temperature of the water reaches around 90 degrees celsius. Be sure the naphthalene completely melted
7. Turn off the heat source and begin recording the temperature every 15 seconds until the temperature reaches 70 C.
8.  Properly dispose of the naphthalene liquid as instructed by the teacher.

Data table

This table is only an example. You need as many rows as there are in around 15 min to be recorded every 15 seconds!!!

complete the table up to 15 min

Graphs

Show the measurements of your data table in a line graph [temp (y)] vs [time (x)]

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 – melting point measured ^oC) / 80.1^oC) x 100

Percent Error = ________%

Analysis questions.

1. What is the formula of Naphthalene?
2. Which is the theoretical value for the melting point of naphthalene?
3. why do we perform the cooling curve of naphthalene instead of the heating curve?
4. How can you tell if the naphthalene used in the lab experiment was pure or not?
5. How can you improve the lab experiment?
6. What happened to the naphthalene (moth ball flakes),  temperature
   
       A) During freezing?

   B) During melting?

7. According to your data and graph, what is the freezing temperature of naphthalene (moth ball flakes),? The melting temperature? Express your answers to the nearest 0.1°C.
8. How does the freezing temperature of naphthalene (moth ball flakes),  compare to its melting temperature?
9. Tell if the kinetic energy of the naphthalene (moth ball flakes),  in the test tube increases, decreases, or remains the same in each of these time segments during the experiment:
   A) When the temperature is changing at the beginning and end of Part I.
   B) When the temperature remains constant in Part I.
   C) When the temperature is changing at the beginning and end of Part II.
   D) When The temperature remains constant in Part II.
10. In those parts of Question 4 in which there was no kinetic energy change, tell if Internal potential energy increased or decreased.