Models in chemistry education : A study of teaching and learning acids and bases in Swedish upper secondary schools

Sammanfattning: This thesis reports an investigation of how acid-base models are taught and understood in Swedish upper secondary school. The definition of the concepts of acids and bases has evolved from a phenomenological level to an abstract (particle) level. Several models of acids and bases are introduced in Swedish secondary school. Among them an ancient model, the Arrhenius model and the Brønsted model. The aim of this study was to determine how teachers handle these models in their teaching. Further, to investigate Swedish upper secondary students’ ideas about the role of chemistry models, in general, and more specific, of models of acids and bases. The study consisted of two parts. First, a study was performed to get an overview of how acids and bases are taught and understood in Swedish upper secondary schools. It consisted of three steps: (i) the most widely used chemistry textbooks for upper secondary school in Sweden were analysed, (ii) six chemistry teachers were interviewed, and, (iii) finally also seven upper secondary school students were interviewed. The results from this study were used in the second part which consisted of two steps: (i) nine chemistry teachers were interviewed regarding their pedagogical content knowledge (PCK) of teaching acids and bases, and (ii) a questionnaire was administered among chemistry teachers of 441 upper secondary schools in Sweden. The results from the interviews show that only a few teachers chose to emphasise the different models of acids and bases. Most of the teachers thought it was sufficient to distinguish clearly between the phenomenological level and the particle level. In the analysis of the questionnaire three subgroups of teachers were identified. Swedish upper secondary chemistry teachers, on the whole, had a strong belief in the Brønsted model of acids and bases. However, in subgroup one (47 %) teachers’ knowledge of how the Brønsted model differs from older models was limited and diverse. Teachers in subgroup two (38 %) and three (15 %) seemed to understand the differences between the Brønsted model and older models, but teachers in subgroup 2 did not explain the history of the development of acids and bases in their teaching. Instead they (as teachers in subgroup one) relied more on the content in the textbooks than teachers in the third subgroup. Implications for textbook writers, teaching, and further research are discussed.