lab 10 - EXPERIMENT 10 TITRATION OF ASPIRIN 07F The Web is...

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EXPERIMENT 10 TITRATION OF ASPIRIN 07F The Web is replete with procedures for the determination of aspirin, acetylsalicylic acid {ASA}, in commercial tablets as experiments for quantitative analysis. The procedure that appeared to be most common was a back titration: adding excess standard NaOH, heating the sample, and then titrating the remaining NaOH with standard HCl – a somewhat tedious procedure. The direct titration was presumed to be inaccurate because of the (possible) hydrolysis (reaction given below and not the same as neutralization) of aspirin during the titration. The structural formula for aspirin is given below. If you open an old bottle of aspirin, you can sometimes detect the odor of acetic acid (vinegar) because of the hydrolysis reaction of aspirin – also given below. O C O O C O CH 3 H 2 O H O C O O H H + CH 3 COOH ASA Salicylic Acid Acetic Acid If one titrates aspirin, acetylsalicylic acid {ASA} directly, one mol of HO - reacts with one mol of ASA, because there is only one acidic proton in ASA. However, if the titration occurs in water, the hydrolysis reaction {above} may occur during the titration and the results will be high because two mol of acid are produced per mol of ASA for some of the ASA. A direct titration is possible in a non-aqueous solvent – one that dissolves ASA, but does not react (at least not rapidly). Alcohols, methanol (CH 3 OH), ethanol (C
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This note was uploaded on 04/13/2008 for the course CHEM 119H taught by Professor Munson during the Fall '07 term at University of Delaware.

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lab 10 - EXPERIMENT 10 TITRATION OF ASPIRIN 07F The Web is...

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