Heating and Cooling Curve of Paradichlorobenzene

HEATING AND COOLING CURVE OF PARADICHLOROBENZENE

Paradichlorbenzene (PDB) is the compound found in what is more commonly called “mothballs”. It sublimes at room temperature and so can be hung in closets in the solid form and the gaseous state is offensive to moths, keeping them out from eating your clothing. It has a melting/freezing point above room temperature, so can be heated and cooled from a solid to a liquid and back. By recording the temperature at regular intervals and plotting the data, a temperature/time heating and cooling curve can be produced. We have seen these graphs, and have discussed the various regions and the kinetic and potential energy changes that occur as heat is added or removed.

MATERIALS

hot plate test tube holder test tube ring stand Vernier “Go Wireless” interface

thermometer

test tube holder temperature probe

paradichlorobenzene (PDB) beakers (400-600 mL x3) ice chips

METHOD

Part A: Cooling of Paradichlorobenzene

1. Set up a hot plate and fill a 400 mL beaker about 2/3 full and heat the water. Use the thermometer to bring the

water to approximately 80oC. Once it reaches approximately 80oC monitor to hold it at this temperature.

2. Obtain a test tube containing PDB and place in the hot water bath. The test tube should be about 1⁄3 full of

liquid PDB when liquefied.

3. Open the Vernier Graphical Analysis app on your iPad that you should have installed (this is a free app).

4. Get a Vernier Go Wireless interface and temperature probe and wait until instructed to turn it on. Do not turn

your link unit on until instructed!

5. When the PDB has liquefied, place the temperature probe in the liquid and use this to monitor the temperature of the PDB.

6. Prepare a cool water bath. The temperature should be kept close to 25oC. You will likely require ice chips to maintain this once you place the hot test tube of PDB in the cold water bath. Use the thermometer to monitor this temperature.

7. Once the temperature of the PDB reaches 70-75oC, start recording data using the “Collect” button on the graph that should be showing on your iPad.

8. Quickly place the test tube into the cold water bath.

9. Make certain you hold the temperature probe in the middle of the liquid and stir gently to obtain an accurate

reading. The PDB should eventually solidify and the probe should be embedded in the solid formed and not be

touching the sides of the test tube for the best results.

10. Continue recording until the temperature has dropped to about 30oC. The temperature of the cold water bath

must be kept at about 25oC for this to occur, so you may need ice chips.

11. Stop recording data and email the data and graph to yourself and your partners.

Part B: Heating of Paradichlorobenzene

1. Place the test tube of PDB in a beaker of ice to further cool it.

2. Prepare a hot water bath by adjusting the temperature of the hot water in the beaker to about 65oC by adding tap

water to cool it. Monitor this temperature