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VISIBLE SPECTROSCOPY PURDUE UNIVERSITY INSTRUMENT VAN PROJECT SPECTROPHOTOMETRIC ANALYSIS OF ASPIRIN (Revised: 1-20-93) INTRODUCTION Aspirin is certainly the most widely used medicinal agent ever discovered. Currently 30,000,000 pounds are sold in the United States each year which provides more than 200 five grain tablets for every person in the country. It is effective as an antipyretic drug (i.e. it reduces fever) and as an analgesic, relieving the mild pain of headaches, neuralgia and rheumatism. The chemical name for aspirin is acetylsalicylic acid. It is an ester derivative of salicylic acid and its common name is derived from the old German version of the name, acetylspirasaeure. Aspirin was first marketed commercially by the Bayer Company in Germany in 1899. The discovery of its important medicinal value was actually a result of earlier studies on the parent compound, salicylic acid, which was shown to have medicinal value, but also some side effects. The highly colored complex which forms between acetylsalicylic acid (aspirin) and iron(III) chloride enables us to determine colorimetrically the specific amount of acetylsalicylic acid present in a tablet. Since the intensity of the color formed is directly related to the amount of acetylsalicylic acid present, a series of solutions, each with a different concentration of acetylsalicylic acid, can be prepared and the absorbance of each solution measured. A calibration curve is then constructed and from this curve the amount of acetylsalicylic acid in a commercial aspirin product can be determined. The complex ion is formed in two steps. First the acetylsalicylic acid is reacted with sodium hydroxide to form the salicylate dianion. Then the addition of acidified iron(III) ion produces the violet tetraaquosalicylatroiron (III) complex.
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VISIBLE SPECTROSCOPY PURDUE UNIVERSITY INSTRUMENT VAN PROJECT OBJECTIVES 1. To use the Spectronic 20 (Spec 20) to determine the milligrams of acetylsalicylic acid (aspirin) in a commercial aspirin product. 2. To compare the mass and cost of acetylsalicylic acid in various commercial aspirin products. PROCEDURE A. Preparation of Commercial Aspirin Solutions 1. Weigh out 0.400 g (400 mg) of acetylsalicylic acid and place it in a 125 mL Erlenmeyer flask. Add 10 mL of 1 M NaOH solution and heat to boiling. Quantitatively transfer the solution to a 250 ml volumetric flask and dilute with distilled water to the 250 mL mark. This solution will be referred to as the "Standard Aspirin Solution." 2. Using a 1 mL graduated pipette, transfer 0.5 mL of standard aspirin solution to a 10 mL volumetric flask or graduated cylinder. Dilute to the 10 mL mark with buffered 0.02 M iron(III) chloride solution. Use a medicine dropper to get the bottom of the meniscus on the 10 mL line. Transfer the solution to a small, clean, dry beaker for mixing and label this "Solution A." 3. Prepare "Solution B" in a similar manner by transferring 0.4 mL of standard aspirin solution as in step 2 and diluting to 10 mL with buffered 0.02 M iron(III) chloride.
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