JOHN J. ALEXANDER University of Cincinnati Cincinnati, 45221
Applying Beer's Law Allan Kahn San Jose State University S a n Jose, California 95192
As students in analytical chemistry learn to use Beer's Law, they can also be made aware of the range of its application and of the need for critical judgment in reading the literature. Cognitive behavior a t the level of synthesis and evaluation is required here. Question In a scientific article the following statement was made: "For a substance which obeys Beer's Law, if the concentration is douhled the amount of light absorhed is more than trebled." Can this statement he true? Explain why or why not. Answer Beer's Law may be stated as laha = 10(1 - Fh") where Iaha and lostand, respectively, for the intensity of absorbed and of incident light; k is a positive constant and x is the concentration of absorbing material. We now investigate what happens when the concentration is doubled
where = &'
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When the concentration of light absorbing material is 0,y = 1. When x is very low, y is nearly 1. And when x is very high, y 0. Thus, the range of values of y which has physical significance is 1 to 0. Clearly the amount of light absorbed when the concentration is doubled ean never be more than doubled. The statement in the article is incorrect.
Volume 55, Number 10. October 1978 1 653
