Experiment: the cooling curve of naphthalene

Materials: test tube, naphthalene, thermometer, hot water, burner, stand, clamp

Be careful as naphthalene vapour is poisonous: you can wear a breathing mask to reduce the risk of you inhaling the vapour

Method

1. Fill a test tube with naphthalene until it is about a quarter full
2. Place the test tube in hot water to allow the naphthalene to melt
3. Insert a thermometer into the test tube
4. When the temperature rises above 90ºC remove the test tube from the water and clamp it
5. Once the temperature begins to fall take readings every 30 seconds
6. Stir the naphthalene while it is cooling
7. When the temperature stops falling stop stirring as you risk breaking the thermometer
8. Continue cooling until the temperature is about 30ºC
9. Once the experiment is complete you will need to melt the naphthalene again so as to be able to remove the thermometer
10. Plot a graph of the results

Results and observation

Cooling curve of naphthalene and results. Image credit askmrtan.com

• The naphthalene’s temperature falls until it starts to solidify
• During the time when it is solidifying heat is given out resulting in no change in temperature
• Once the solidification process is complete the temperature of the naphthalene begins to fall again

To access more topics go to the Combined Science Notes page.