Organic Chemistry 250
RECRYSTALLIZAION OF NAPHTHALENE FROM A MIXED SOLVENT
The purpose of this experiment, crystallization and recrystallization is to separate and purify compounds. In this case, naphthalene. A solid containing undesired impurities is dissolved in a small amount of solvent, cooled allowing the crystals to form then filtered out. An ideal solvent will dissolve the solute when solution s hot not when the solution is cold. Either can dissolve impurities very well or not at all.
1. Add 2 g of impure naphthalene to a 50 mL round bottom Erlenmeyer flask with a condenser.
2. Add 25 mL of methanol, heat up the solution to the boiling point (65◦-66◦ C) to dissolve most of the solid. Boil using the voltage transformer at 60-80V.
3. Filter through a fluted filter paper in a previously warmed solvent, then funnel into a 150 mL Erlenmeyer flask, this method is gravity filtration.
4. When the filtration is complete, the volume of methanol should be 15 mL. If not the excess methanol should be evaporated.
5. Heat the solution to boiling point, then add water drop-wise with a pipette, no more than 3.5mL of water should be used.
6. Remove the flask from the heat, place it on a cork ring and cool it down to room temperature without being disturbed.
7. Collect the solid by suction filtration using 30:7 cold methanol and water to rinse it.
8. Weigh the product and test for the melting point in degrees Celsius.