Qualitative and Colorimetric Analysis of Salicylic Acid The experiment described here, combining the qualitative test with ferric chloride (1) and the colorimetric snalysis of salicylic acid in body fluids, (2) was developed to meet the needs and interests of students with nontechnical majors. Both the lectures and experiments emphasize the most important concepts and applications of chemistry with some analysis of social and consumer problems involving seience and technology. An important aspect of every experiment is an explicit introduction to a specific real problem and a description of how this translates into chemical cancepts and s laboratory procedure. The necessity for the analysis of potentially toxic salicylic acid in body fluids is readily perceived by students as a specific example of an important general type of laboratory problem: quantitative analysis. Each student receives an extensive introduction which includes a description of the properties and uses of aspirin (3, 4). This opportunity is taken to discuss the hydrolysis to salicylic acid and the interesting correlation between solubility and stomach bleeding (5, 6). In the first part of the experiment, the student is provided a report form with reproduced structural formulas for acetic acid, acetylsalicylic acid, benzoic acid, ethanol, phenyl acetate, phenol and salicylic acid. Utilizing 10 ml samples of 0.1% aqueous solutions of these com~oundsand a 1% ferric chloride solution. the student determines which iunctional group or combination of functional boupsis necessary for color formation. In the second part, the quantitative analysis, the method of Tietz (2) has been modified to utilize the laboratory skills students have acquired. Having developed the color for a series of aqueous solutions of known concentrations of salicylic acid and a urine sample, the students estimate the concentration by eye. Then the instructor or laboratory assistant operates the calorimeter, explaining the instrument operation and the use of sample blanks. Students prepare Beer-Lambert plots and determine the concentration of salicylic acid in the urine sample. This experiment was designed to (1) develop the concept of functional groups as part of the larger concept of correlation of observed properties with submicroscopic structure, (2) differentiate between qualitative and quantitative analysis. (3) demonstrate the qualitative relationship between concentrations and the intensity of color observed, and (4) use the colorimeter to demonstrate the Beer-Lambert Law and determine concentrations. Our purposes do not require producing results of high accuracy and precision although the methods are more than satisfactory. The experiment has proved valuable because it achievesthe purposes stated, is viewed as practical and interesting, and produces good results utilizing the elementary techniques these inexperienced students have acquired. One disadvantage has been the unexpected queasiness of certain students to obtain, handle or talk about urine samples and the difficulty of obtaining blood samples. Therefore, the experiment has been revised to supply solutions of "artificial blood serum." These solutions are isotonic sodium chloride solutions with added salicylic acid and food color.
Literature Cited 11) Shrinar, R. L., Fuson, R. C.. and Curtin. D. Y.. "The Syatsmatie Identifieation of Organic Compounds," 6th ad.. John W i c y and Sans, Ine.. New York,
,w, " >"" ...",r..-.. (21 Tiotz. N. W.. "Fundamentaisof Clinical Chsmirrv." W. B. SaunderaCo..Philadslohia. 1970. o.882.
StephenC. Hoops ~ e n n s y l v s h i aState University-New New Kensington. 15068
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Journal of Chemical Education
Kensington Campus
