Examining Strategies Used by Pre-service Science Teachers in Stoichiometry Problems in Terms of Proportional Reasoning

Stoichiometry problems are one of the best examples of problem solving in chemistry education. Proportional reasoning supports correct answers in stoichiometry problems. It is needed to examine how these problems are solved as well as the accuracy of solutions because of the importance and benefits of conceptual problem solving. This study utilizes the embedded multiple case study design. The stoichiometry problem solutions of 37 pre-service science teachers (PSTs) were examined based on three units of analysis; (i) whether pre-service teachers balanced the equations correctly or not, (ii) the accuracy of solutions, and (iii) strategies used to solve problems. More than half of the PSTs balanced the equations correctly but most of them did not interpret the integers in the equations appropriately. Participants were inclined to use algorithmic approach more than proportional reasoning. The accuracy of solutions and the frequency of algorithmic approach increased while the complexity of problems decreased. PSTs had difficulties in making sense of integers of chemical reactions, using intensive units such as density, and converting units. It is thought that PSTs prefer to use strategies that they learnt in their prior learning experiences. Within the context of findings, we suggest that PSTs should be supported conceptually about the meanings of integers and should be introduced using proportional reasoning in problem solving prior to algorithms