Paradichlorobenze

Title:

Freezing and Melting of Paradichlorobenzene

Purpose:

Melting, freezing, and boiling points are properties that can easily be determined and help in identifying a substance. These properties can be found in chemical literature ad reference tables, and can be used to distinguish a pure substance from many other pure substances. In this lab you will use the pure substance Paradichlorobenzene and determine its melting an freezing points by warming and cooling a sample of the substance, then plotting heating and cooling curves and analyzing them. Data that you collect will represent the heating and cooling behavior common to all pure substances.

List of Materials:

-Large Test Tube (18*15 mm) -Safety goggles -Paradichlorobenzene

-Hot Plate -Lab Apron -Acetone

-Test Tube Holder -Ring Stand

-2 Thermometers -A Ring Clamp

Procedure:

1. Make a data table with headings for time, temperature of Paradichlorobenzene, and temperature of water.

2. Fill a 250mL beaker about 3/4th full of cool tap water. Place a thermometer in the beaker and record the temperature to the nearest 0.2C

3. Obtain a test tube containing solid Paradichlorobenzene from your teacher and gently heat the test tube over a medium Bunsen burner flame. Move the test tube in and out of the flame at a slight angle.

4. Once the Paradichlorobenzene has melted, remove it from the flame and shut the gas valve off.

5. Before moving on to part I, fill up another 250mL beaker 3/4th full of cool tap water and begin to heat up a hot plate on medium to high heat.

Part I - Cooling of Paradichlorobenzene

6. Put a thermometer into the test tube of melted Paradichlorobenzene. Record the temperature in your data table.

7. Lower the test tube into the beaker of water until all of the Paradichlorobenzene is under water. Fasten the clamp onto the ring stand.

8. Wait 30 seconds. During that time, stir the Paradichlorobenzene by moving the thermometer up and down. At the end of 30 seconds record the temperature of the Paradichlorobenzene.

9. Continue to record the temperature of the Paradichlorobenzene every 30 seconds. Also take the temperature readings of the water in the beaker every 60 seconds. Stop timing when the temperature of the Paradichlorobenzene and the water are within 3-5 degrees of each other.

10. After completing this part of the experiment, remove the test tube from the water, and leave it clamped to the ring stand. Leave the thermometer stuck in the test tube.

Part II - The Warming of Paradichlorobenzene

11. Remove the heated beaker of water from the hot plate and turn the heat off. Adjust the temperature to about 70 degrees Celsius.

12. Lower the test tube into the warm water until all of the Paradichlorobenzene is under water, then clamp the test tube in place.

13. From the moment you clamped the test tube, wait 30 seconds and as before, record the temperature of the Paradichlorobenzene at the end of the 30 seconds.

14. Continue recording the temperature of the Paradichlorobenzene every 30 seconds and of the water every 30 seconds.

15. When the temperature of the Paradichlorobenzene is within 3-5 degrees of the temperature of water, stop recording and remove the thermometer from the liquid,