Introduction:The purpose of this experiment is to create and isolate pure acetylsalicylic acid from the substances salicylic acid and acetic anhydride. Then one will find the melting point to determine purity.
Procedure:Make a hot bath. Weigh some salicylic acid and place in conical vial. Add .480mL of acetic anhydride and a drop of concentrated phosphoric acid. Drop in a magnetic spin vane and attach air condenser to vial. Partially submerge it in hot water. Stir with spin vane to dissolve salicylic acid. After mixture dissolves, heat for 8 to 10 minutes. Crystallize the Acetylsalicylic acid by cooling the mixture. Then add 3.0mL of water and stir.
Set up a Hirsh funnel for vacuum filtration. Add 1mL of cold water to help transfer all of crystallized substance. Rinse crystals with water once all collected in funnel. Let crystals dry in funnel. Let finish drying on a watch glass for the week. After a week take the product, and weigh it in a pre-weighed beaker. Calculate the percent yield.
Test for Purity. Take 3 test tubes filled with water and dissolve a little bit of crystals in the first 2 tubes. Add 1 drop of 1% ferric chloride solution to each tube. Shake and note color. If impure, red to violet color will appear. Melting point can be used to test for purity. Melting point from a dry sample should be 135-136°C for pure aspirin. There are impurities if much less than that.
Data and Calculations:
Amount of Salicylic Acid 0.216g
Amount of Acetic Anhydride 0.480g
Amount of final product (acetylsalicylic acid) 0.144g
0.144g Acetylsalicylic Acid
0.216g Salicylic Acid X 100% = 66.667%
Melting Point: 120-123°C
Ferric Chloride Test:
Test Tube ContentResults
Salicylic AcidDeep Purple
Acetylsalicylic Acid (Product)Light Lilac
Water (control)Clear& Colorless
*All tubes contain 0.5mL of water
Results and Discussion: