Secondary school students' conceptual understanding of physical and chemical changes

In recent years, researchers have shown an interest in understanding students’ own ideas about basic chemical principles and guiding them through innovative ways to gain conceptual understanding where necessary. This research was a case study designed to assess 50 first year high school students’ conceptual understanding about changes in matter, with interpretive underpinnings. A diagnostic probe was administered to find out if discrete particles could be used to differentiate chemical changes from physical changes and to unravel the different conceptual interpretations that students had. Submissions obtained from the students were classified on levels of conceptions, and analysed using frequency counts and percentages, after which an interview was conducted to gain a deeper insight into their unscientific submissions. Findings from the study indicated that only a few students had difficulties in distinguishing between physical and chemical changes. These few did not associate the changes in states with associated physical and chemical properties, as was expected at their level. Neither did they base their explanation on the breaking nor formation of bonds, nor with changes in the constitutions of entities. They overwhelmingly intimated that physical changes were reversible whilst chemical changes were not. About 38% of participants who provided correct definitions for physical and chemical changes in two of the probes could not assign reasons for them. However, almost 79% of the participants showed an appreciable knowledge of types of changes that occur in chemistry. The adopted diagnostic probe and interview were useful in identifying students’ alternative conceptions about changes in chemistry. Diagnostic probes are recommended as a pre-requisite for conceptual change strategies.