Purity of Aspirin by Spectrophotometry

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Experiment 7a
Title: Purity of Aspirin by Spectrophotometry
Aim: i. To measure the absorbance of different volumes of sodium salicylate solutions and aspirin with iron chloride
ii. To find the concentration of each standard solutions
iii. To determine percentage purity of aspirin.
Abstract:The mass of acetylsalicylic acid was determined using a analytical balance. Sodium hydroxide (NaOH) was added to the acetylsalicylic acid and heated in order to hydrolyze acetylsalicylic acid. Iron chloride was added to each volumetric flask as the purity of the aspirin can be tested by addition of Fe+3 to a suspension of the product. Phenols such as salicylic acid react with iron chloride to form coloured (violet) complexes Aspirin easily absorbs green light and green is the compliment of violet, which allows a determination of the amount of aspirin present. The percentage purity of aspirin was found to be 90.62%. Aspirin tablets (about 5-grams) are usually compounded of about 0.32 g of acetylsalicylic acid, which indicates that aspirin should be about 94% pure. The calculated value for aspirin content was close to the true value and indicates that aspirin sample tested was very pure. .Introduction

Aspirin is a member of a family of chemicals called salicylates. This chemical can be converted (changed) by the body after it is eaten to another chemical, salicylic acid. Salicylic acid may be irritating because it is an acid; therefore one of the acidic parts was covered up with an acetyl group, converting it to acetylsalicylic acid (ASA). ASA not only could reduce fever and relieve pain and swelling, but better for the stomach and worked even better than salicylic acid. Salicylic acid produces a salicylate dianion, when dissolved in water, which reacts with an acidic solution Fe (NO3)3(aq), to produce a strong violet tetraaquosalicylatroiron (III) complex. The violet color of the complex results from the fact that the complex strongly absorbs...
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