Lab Recrystallization Organic Chemistry

Recrystallization

I. Determining the Best Recrystallizing Solvent

1. Obtain four large test tube.

2. Place a pea size amount of benzoic acid into each test tube.

3. Place 1 mL of each solvent in Table 1 on the data sheet into each of the different test tubes.

4. Stir the solution with a glass stirring rod. Try to dissolve all of the benzoic acid into the solvent. If benzoic acid dissolves in the solvent, write S for soluble in both hot and cold. Note the amount of time it takes for the compound to dissolve in your lab notebook.

The sample is considered dissolved when the solution is clear with no cloudiness or solid is apparent. A solution of dissolved solute may have color however it is still considered dissolved if no solid is apparent. If you observed any solid on the bottom of the test tube, floating on the top of the solvent or dispersed in the solvent (cloudy) the sample is considered not to have dissolved.

5. If benzoic does not dissolve in the solvent, try adding another 4 milliliter of solvent to the test tube. If benzoic acid dissolves in the solvent, write S for soluble in both hot and cold. If benzoic acid still does not dissolve, write I for insoluble in cold.

6. If benzoic acid is insoluble in the cold solvent, place the test tube into a hot water bath. Be careful not to let the solvent boil off, add more solvent to the test tube if the volume of the solvent gets low.

7. Determine whether the solvent is soluble or insoluble in the hot solvent.

8. Repeat steps 1-7 for cinammic acid, acetanilide, urea.

9. Write in your notebook whether the sample precipitated when the sample was cooled. Note the ease of formation, the amount, size and shape of the precipitate.

10. Determine the best recrystallizing solvent for each compound.

II. Recrystallization of napthalene

Dissolving the compound

1. Weigh out approximately 1 gram of impure napthalene. Record your mass...