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Part 2. Recrystallization of Aspirin

Schedule

Detailed schedule and instructions for the prelab, the lab report and the required reading This schedule is unofficial and subject to modifications.
Prelab					Report
Instructions + Supplementary Material	Evaluation	Required Reading - to be done before the experiment			Instructions + Information	Evaluation
		Lab Manual by Turkewitsch	Lab Textbook Macroscale and Microscale Experiments 5th edition by Williamson	First-year chemistry textbook Chemistry: The Central Science 13th edition by Brown, LeMay and Bursten
Part 2. Purification of aspirin by recrystallization After having read the required reading and the procedure provided below, prepare a prelab as follows: 1. Prepare data tables following the example in the Chemistry Guide. 2. Answer the following prelab question: Draw the molecules of acetylsalicylic acid and ethyl acetate. List the types of attractive intermolecular forces that are likely to exist between these two (2) molecules and place them in order of decreasing strength. Provide a separate labeled drawing for each intermolecular force. One example of each force is sufficient. Do not forget to use arrows to describe and/or identify precisely the components of the diagram, and what is represented by the diagram (for example, the formation of an intermolecular force, etc.). Cite your sources.	The prelab for Part 2 will be marked before the beginning of the lab session.	Section - Lab notebook & prelab assignment provides information on how to prepare your prelab	Chapter 4 Recrystallization	---	Hand in the report sheet at the beginning of the next lab period or one week after the lab work has been completed.	Lab Report Sheet Recrystallization of aspirin

Safety

Detailed schedule and instructions for the prelab, the lab report and the required reading
This schedule is unofficial and subject to modifications.
Some of the chemicals used are irritants, are toxic and are suspected carcinogens. It is always wise to assume that the chemicals used are toxic and take necessary precautions. Be careful when handling all chemicals.
Always wear a lab coat, wear safety glasses and gloves, even while cleaning up and washing glassware.
Always work under the hood with the sash lowered as far as possible. Avoid breathing the vapours.

Cleanup and disposal

All solutions and mixtures are to be placed in the designated waste receptacle for that purpose. Under no circumstances are the solutions or mixtures to be flushed down the drain. If you are unsure of how to handle a solution, ask your professor or the lab technician. Throw used rinsed test tubes in the glass waste box.

Experimental procedure

Recrystallization of Crude Aspirin¹

Before beginning the recrystallization of crude aspirin, do not forget to examine and weigh the crude aspirin crystals. Note the exact mass of crude aspirin crystals obtained.
Place a small amount of crude aspirin, about 20 mg (verify wtih your professor), in a vial for use in the analysis. The remainder of the crude aspirin will be recrystallized from ethyl acetate following the procedure directly below.
Take out a 10-mL Erlenmeyer flask and a reaction tube. Make sure the reaction tube is clean.
Fill the Erlenmeyer flask with approximately 5 mL of ethyl acetate (the recrystallization solvent) and place a boiling stick in the liquid.
Fill a 50-mL beaker with 20 mL of distilled water and place it into an ice-water bath to cool. This ice-cold distilled water will be using during the vacuum filtration step below.
To add the crude aspirin crystals into the reaction tube, place the reaction tube on the electronic balance, re-zero the balance, add the crystals and note the exact mass of crude aspirin to be recrystallized.
Heat the ethyl acetate on a hot plate to just within a few degrees of the boiling point and maintain at this temperature. Watch it closely!
To the reaction tube, add the hot ethyl acetate dropwise. Once the solid is wet enough, with constant swirling, heat the mixture in a hot water bath (maintained at about 90ºC) to just before the boiling point. Wait long enough between additions of solvent to allow for the dissolution of the solid to occur. However, once the mixture begins to boil, remove it from the hot water bath to avoid evaporating the solvent that you have just added. With constant swirling, maintain the mixture to within a few degrees of the boiling point.
Once the crude aspirin crystals have completely dissolved, note the approximate volume of ethyl acetate using the graduatins on the reaction tube.
Remove the reaction tube from the hot-water bath and place it at the back of the hood to cool at room temperature. Do not touch it while it is cooling!
After approximately 5 minutes, place the tube into an ice-water bath to allow complete crystallization to occur. If crystallization does not begin, rub the sides of the flask with a glass stirring rod to induce the formation of crystals.
Filter the cold mixture by vacuum filtration using a Hirsch funnel. Use ice-cold water, and NOT ethyl acetate, to help in transferring the crystals and to wash them. Maintain suction for a few minutes to air dry the crystals before transferring them (with the filter paper) onto the watch glass (labelled and preweighed).
Allow the crystals to dry for a few days.
Come back in two or three days to examine and weigh the recrystallized aspirin.
Calculate the percentage yield of the reaction as well as the percentage recovery of the recrystallization.

References

Williamson KL, Minard R, Masters KM. Chapter 4, Recrystallization. In: Macroscale and microscale: organic experiments. 5th edition. Boston: Houghton Mifflin; 2007. p. 78.