Diagnosing teacher candidates’ reasoning on solution concentration: a theoretical analysis of definitional and procedural difficulties

This study examines teacher candidates’ reasoning about solution concentration units (mass percent, molarity, and molality), with a focus on difficulties seen in definitional tasks and item-based applications. A 12-item diagnostic test informed by Cognitive Load Theory (CLT), Dual Process Theory (DPT), Conceptual Change Theory (CCT), and Representational Competence Theory (RCT) was administered to 152 teacher candidates. Additionally, semi-structured interviews were conducted with purposefully selected teacher candidates to clarify the reasoning routes underlying their response choices. Quantitative findings showed an overall accuracy of 70.29%, but performance was notably low on some items ( e.g. , Item 5: 32.30%), particularly when tasks required coordinating unit meaning with the correct referent and managing conversions and proportional reasoning. Error coding revealed recurring response patterns across five categories: definitional confusion (DC), unit mistake (UM), ratio-reasoning mistake (RR), superficial decision (SD), and computational mistake (CM). Interview evidence suggested that, within the formats of this instrument, some teacher candidates relied on cue-based responding and limited checking rather than explicitly grounding choices in the intended referent meaning ( e.g. , solution volume vs. solvent mass). Interpreted through CLT, DPT, CCT, and RCT, the findings suggest that effective instruction may require more than definitional recall and routine calculation. It may also benefit from supports that explicitly connect formula, unit, and problem context and encourage checking during problem solving. The study aims to contribute to chemistry education research by offering a theory-informed interpretation of recurring error patterns in concentration tasks based on integrated test and interview evidence.