A Didactic Sequence Inspired by the Historical Evolution of Colorimetry to Introduce the Lambert–Beer Law at High School Level

This research paper aims to propose a novel didactic sequence inspired by an historical / epistemological study of the evolution of spectroscopy and in particular of colorimetry. The working principles of the historical color comparators and the visual color matching method, first proposed by Duboscq, stimulated us in the development of a five-steps sequence of experiments, following a phenomenological approach. The teaching sequence was designed to help students understanding several key-aspects of the well-known and widely used Lambert-Beer equation, which is typically introduced to high school students for analytical chemistry applications. Through the proposed laboratorial experiences students should understand the meaning and the role of the optical path and of the concentration of the solution in the color intensity. Moreover, students should realize that the intensity of color is determined by the number of absorber particles the light encounters during its optical path. The didactic sequence has been experimented with 95 high school students from four different institutes and a qualitative study was carried out based on the analysis of students’ answers to a 15 open questions survey which was specifically designed to investigate students’ misconceptions, way of reasoning and understanding of the main aspects related to the phenomenon of light absorption of a colored solution. The main results of the experimentation based on the analysis of the questionnaires are here reported and discussed. The description of the sequence and relevant technical aspects together with the materials useful for high school teachers are also provided.