Resumen de Using Particulate Drawings to Determine and Improve Students' Conceptions of Pure Substances and Mixtures
Students were interviewed to identify the ways in which they classify particulate drawings as pure substances or heterogeneous or homogeneous mixtures. Those who successfully classified the heterogeneous and homogeneous mixtures used a "randomly mixed" definition. Unsuccessful students were more likely to use a "visual" or "sampling" definition. Some students' difficulties in classifying these drawings can be attributed to their applying macroscopic definitions (such as the visual or sampling definitions) to microscopic drawings. An instructional lesson was developed that incorporated the randomly mixed definition, computer-generated visuals at the microscopic level, and physical samples of these substances at the macroscopic level. It was administered to another set of students. Those who received this instruction were more likely to correctly identify particulate drawings of liquids, pure compounds, heterogeneous mixtures, homogeneous mixtures, elements, and compounds than students who received traditional instruction. As a result of the new lesson, students' interpretations of particulate drawings of pure compounds and heterogeneous and homogeneous mixtures appeared to evolve from the assumption that all mixtures are heterogeneous and that pure compounds are homogeneous mixtures to the correct classifications.
