Synthesis

1. Go to the fume hood, where your teacher will place 8–10 drops of acetic anhydride in your test tube and then will add 3–4 drops of sulfuric acid. Be sure your lab partner stays at the lab bench to keep watch over the water bath on the hot plate.

2. Take the tube back to your lab station. Heat the test tube and contents in the hot (boiling) water bath for approximately 3 minutes.

Purification

1. Remove the test tube from the hot water bath and use the plastic pipet to cautiously add 10 drops of water to the tube.

2. Stopper the test tube and shake it well.

3. Carefully remove the stopper and place the test tube in the ice bath. Allow the tube to remain in the ice bath for at least 5 minutes. Observe and record your observations as it cools.

4. Use a pipet to remove as much liquid as possible from the crystals that have formed.

5. Add enough hot water to just dissolve the crystals.

6. Cool again and new crystals should form.

7. Rinse the pipet and once again use it to remove as much liquid as possible from the crystals that have formed.

8. Place the crystals on a piece of filter paper and place this on a watch glass to dry overnight.

Analysis (the next day)

1. Examine the crystals under a magnifying glass and record your observations.

2. Find the mass of the dry crystals and record this amount in your lab notes.

Follow-up (optional)

1. Test the product for relative purity as follows. Place a few crystals of salicylic acid in one test tube; in a second, place a little crushed commercial aspirin; in the third test tube, add a few crystals of your prepared acetylsalicylic acid. Now add a few drops of iron(III) chloride to each tube and shake to mix the contents. Observe and record the results.

2. You can also test the relative purity of a sample by determining its melting point. Typically, pure compounds have a distinct melting point. The wider the range of temperatures between the point at which you see the first signs of melting and the temperature at which all melting has finished, the less pure the mixture. Your teacher will give you the procedure for determining the melting point of your synthesis product.

3. Your teacher may also want you to analyze the composition of your product using a spectrophotometer. He or she will provide procedural details.

 

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