James S. Proctor and John E. Roberts University of Massachusetts
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Analysis of Aspirin:
Student interest often can be increased or even turned into enthusiasm by using other than the conventional reagents in an analytical experiment. We have found this to be true when students were asked to determine the amount of aspirin in a regular (5 grain) or children's size (1.25 grain) tablet. Total acidity can be assumed to be acetylsalicylic acid, formula weight 180.2. The figure shows typical student data obtained with a solution of one 5-grain tablet in 500 ml HzO; aliquots were employed in a conductometric titration. A Fisher Titrimeter can be used, but we have found that quite satisfactory results can be obtained by using instruments available in kit form which have been designed as resistance-capacitance testers to sell for about $20.00.' They operate on 60 cycle ac and use an electronic mill indicator. Although the potentiometer slide-wire in these is not uniformly linear, if 1 Among other sources, instruments of the type described can be obtained from (a) Allied Radio Corporation, 100 N. Western Avenue, Chicago 80, Illinois, No. 83Y124 Knight-kit R/C tester; and (b) Heath Company, Benton Harbor, Michigan, Model C-3 Condenser Tester.
A Conductometric T h t h
conditions and cell constant are such that the middle t,wo-thirds of the scale are used, errors are probably less than those inherent in graphical evaluation of the data.
MIUIEQUIVALENTS OF TITRANT Figure 1.
DireO tin'otion of aspirin.
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Volume 38, Number
9, Sepfember 1961
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471
