Purpose To determine the purity of aspirin obtained from preparation from a solution of salicylic acid and acetic anhydride by acid-base titrations; to become acquainted with the concept of back-titration analysis. Discussion of Theory While most commercial aspirin contains a majority of acetylsalicylic acid, not all tablets are 100% pure. These aspirin tablets contain a binding agent which holds them together. Titration is then used to determine the purity of aspirin. Procedure 0.5g of aspirin was placed in a 250 mL Erlenmeyer flask. Two burets were filled to the top, one o with an acidic solution and one with a basic solution. Next, 25mL of 95% ethanol at 15 C was added to the flask and swirled to dissolve the aspirin. 2 drops of phenolphthalein were added to the flask and the contents of the flask were titrated with 0.1M NaOH (basic solution). The contents were titrated until a faint pink color appeared in the flask. The reading for the buret was recorded. Data Prepared Aspirin Molarity of NaOH: 0.1M Molarity of HCl: 0.1M Mass of aspirin: 0.5g Volume of NaOH Required to Neutralize All Acid Material Final reading: 73.5mL Initial reading: 100mL Volume of NaOH: 26.5mL Millimoles of NaOH: 1410 mmol Analysis Grams of acetylsalicylic acid in sample: 0.49g Percent of Aspirin: 98% Average percentage of aspirin: 98% Standard deviation from the mean: 0 Calculations
Conclusion At the end of this experiment, it was determined that all forms of aspirin are not 100% pure acetylsalicylic acid. These impurities can be determined using the process of titration, where detective chemical reagents are used to determine the presence of these impurities. Back-titration does not necessarily have to be used as it is only needed to create more accurate sets of data. If the solution is accurate enough, it can be left the way it is.
