Lauric Acid Lab

Purpose:

In this investigation, you will observe the melting and freezing behavior of lauric acid (C12H24O2). You will measure the temperature at timed intervals as the lauric acid is heated and cooled and determine experimentally its freezing point and melting point.

Pre-Lab Questions:

1. Define melting point and freezing point. 2. Describe what happens to the particles of a solid as it is undergoing melting.

Procedure:

1. Put on goggles. Set up computer and logger pro as directed by your teacher. 2. Fill one beaker ¾ full with tap water and heat it to about 60C. Place the test tube containing lauric acid in the beaker while it is heating up. Attach a test tube holder near the top of the test tube and place in the hot water bath. Melt the lauric acid completely. 3. Use hot and cold tap water to fill a second beaker ¾ full of water to 30C. 4. Using the test tube holder, remove the test tube from the hot water bath and place it in the cool water bath. Make sure the level of water in the beaker is above the level of the liquid in the test tube. Also, double check to make sure the temperature is 30C. 5. Put the temperature probe into the test tube. Start the temperature readings making sure that you are stirring the lauric acid continuously. 6. When the sample is mostly solid, stop stirring. Continue to take temperature readings until the temperature of your sample has fallen to about 40C or below. 7. Adjust the hot water bath to 50C if necessary. 8. Remove the test tube from the 30C water bath and place it in the beaker of water at 50C. Immediately begin to take temperature readings every 30 seconds. Begin stirring gently as soon as you are able to move the thermometer easily. Continue to measure and record the temperature until the lauric acid is about 50C or above. 9. Remove the temperature probe from the lauric acid and return the test tube to your teacher. Do not pour this down the sink!! 10. Rinse off any lauric acid on the temperature probe by placing it into the warm water bath. Dry off with a paper towel. 11. Clean up your workstation and wash your hands. Questions:

1. On your graph, circle where melting and freezing are taking place. Record an approximate temperature for melting and freezing.

Melting point ______Freezing point ______

2. Does lauric acid freeze and melt at the same temperature? How do you know?

3. Explain the shapes of the graphs in terms of energy changes that occur as the lauric acid heats up and melts and as it cools down and freezes.

4. What effect would increasing the amount of lauric acid have on the melting point and the shape of the graph?

Conclusion: