Grade 12 Chemistry
Lab – Preparation and Testing of Aspirin
Purpose: To prepare a sample of acetylsalicylic acid (ASA), more commonly known as aspirin, and to test
its purity compared to commercial aspirin. Aspirin is made by the reaction of salicyclic acid and
acetic anhydride, as shown below.
Materials: List all the equipment and chemicals you used in the lab. You must wear safety glasses
throughout the lab. Make the list as you go along. Include labeled diagrams of the reaction set up, the
filtration apparatus, and the melting point apparatus to avoid long lists of all the separate components.
(4 marks)
Procedure:
Part 1 – Preparation of Aspirin
1) Obtain a sample of about 4 g of salicylic acid in the following way: Zero a 125 mL Erlenmeyer on the
balance, and then determine the mass of the salicylic acid by measuring it directly into the flask.
2) Go to the fumehood, and add approximately 8 mL of acetic anhydride to the flask. Stir the mixture with a
stirring rod. Add 4 drops of concentrated sulfuric acid while you continue stirring.
3) Clamp the flask containing the mixture in a 600 mL beaker of boiling water (with boiling chips!) and
clamp it into place. Allow the reaction to proceed for about 10 minutes.
4) Fill a 150 mL beaker about one third full of crushed ice and water. Take the flask out of the water bath,
and then pour its contents directly into the ice water. Rinse the flask with another small amount of ice water
in order to transfer all the aspirin into the beaker. The ASA should recrystallize out of solution at this point.
5) Allow the product mixture to cool down completely, stirring it until recrystallization appears to be
complete (ie. until no more white solid is formed).
6) Find the mass of a piece of dry filter paper. Filter the crystals using the filter paper and a funnel in a ring
clamp. While filtering, wash the crystals with small amounts of ice water three times.
7) Find the mass of a clean, dry watch glass. Dump the aspirin and the filter paper onto the watch glass, and
place it in the prep room, with a label to identify it. After one night drying, find the mass of the aspirin, the
filter paper and the watch glass.
Part 2 – Testing the Purity of the Aspirin
a) Melting Point: Your teacher will do this for the whole class at the front of the room.
1) Get two capillary tubes, and fill them with your prepared ASA and commercial aspirin by pushing the end
of the capillary tube into the chemical and then tapping gently until it moves up the tube a little. Do not
confuse the two substances once they are in the capillary tubes!
2) Attach the tube to a 150 C thermometer with a small circle of rubber tubing. Place the apparatus into the
oil-filled Erlenmeyer flask, hold it steady with a ring clamp attached to a retort stand, and then heat the oil
bath using a hot plate.
3) Heat the oil gradually, watching the capillary tubes for signs of melting when the temperature approaches
120 C. At the first sign of melting, record the temperature for the prepared and the commercial ASA.
b) Acidity:
Place a few crystals of your aspirin and of commercial aspirin on a piece of moist blue litmus paper. Record
your observations.
c) Chemical Test:
1) Put three test tubes in a test tube rack, add a few crystals of salicylic acid (the reactant) to the first test
tube, your prepared aspirin to the second test tube and commercial aspirin to the third test tube.
2) Come to the front of the room and add one dropper full of methanol to each test tube and shake the test
tube to dissolve the solid. Then add one or two drops of 0.1 M ferric chloride solution to each test
tube. Make observations.
Observations:
Qualitative: Describe using physical properties and full sentences.
a) Describe the reactants, the reaction and the products. (4 marks)
b) Describe the litmus test for the prepared and the commercial ASA. (1 mark)
c) Describe the 0.1 M FeCl3(aq) / methanol test for the prepared and commercial ASA and also for salicylic
acid. (1 marks)
Quantitative:
mass of salicylic acid used (g)
mass of filter paper (g)
mass of watch glass (g)
mass of filter paper + watch glass + prepared ASA (g)
mass of prepared ASA (g)
melting point of prepared ASA (°C)
melting point of commercial ASA (°C)
Questions:
Show all units and chemicals used in your calculations, all steps of your work and paraphrase your answer
with the correct number of significant digits for full marks.
1a) Calculate which reactant is the limiting reagent (assume that the density of acetic anhydride is
approximately the same as that of water). (4 marks)
b) Use the limiting reagent to calculate the theoretical yield of your ASA.
(3 marks)
c) Calculate the % yield of your prepared ASA. (2 marks)
2a) The melting point of pure acetylsalicylic acid (ASA) is 136 °C. Compare this value to the melting point
test of the prepared and commercial ASA. There are probably some differences between the melting points
of commercial ASA, your prepared ASA and pure ASA. Suggest specific reasons for this, commenting on
both the prepared ASA and the commercial ASA. (3 marks)
b) Use the results of the acidity and chemical tests to compare the purity of your prepared ASA to the
commercial ASA. Are these tests as accurate as the melting point test? Why? (3 marks)
Conclusion: Summarize all the results of your experiment. (3 marks)
Suggest at least two major sources of error that affected the % yield of the prepared ASA.
(2 marks)
TOTAL: Thinking/Inquiry: ________ / 30
Communication: _________ / 10