Determination of the Amount of Acetylsalicyclic Acid in One Tablet of Commercial Aspirin

(I) Experimental objective The percentage of acetylsalicylic acid in commercially available aspirin tablets was determined using the principle of back titration. (II) Discussion Post-use titration is used instead of direct titration because there are no suitable indicators for acetylsalicylic acid and sodium hydroxide solution. Therefore, it is reacted with acetylsalicylic acid using excess NaOH. The number of moles of unreacted NaOH was determined by titration with hydrochloric acid. Finally, the number of moles of acetylsalicylic acid and its proportion in the commercially available aspirin tablets were estimated.

Despite your best efforts, your previously synthesized aspirin may not be pure. The most likely impurity is acid - salicylic acid (unreacted starting material) or acetic acid. Even commercially available aspirin tablets are not 100% acetylsalicylic acid. Most aspirin tablets contain a small amount of binder to prevent tablet breakage. Binding agents are chemically inert and intentionally added by the manufacturer, but their presence means that aspirin tablets do not have 100% purity. In addition, moisture can hydrolyze acetylsalicylic acid. Therefore, aspirin which is not dried can be decomposed. Acetic acid is a hydrolyzate formed by the reaction of water and acetylsalicylic acid.

HA (aq) + NaOH (aq) -, H 2 O (1) + NaA (aq) (1) Acidic base salt The common chemical name of aspirin and the common chemical name of aspirin is acetylsalicylic acid. To determine the amount of aspirin (acetylsalicylic acid) in the sample, it is necessary to know the exact amount and concentration of NaOH and the total reaction. NaOH is used as a secondary standard because concentration may change over time. In order to determine the exact concentration of NaOH, completely water soluble acid with high molar mass has to be titrated according to the primary standard. It is pure even if left to stand, it does not absorb moisture. . Since sodium hydroxide is hygroscopic, it absorbs moisture from the surrounding environment. Therefore, the most common way to determine the concentration of sodium hydroxide solution is titration. Using the main criteria to determine the exact concentration of NaOH is called normalization.