Date of Award
Program or Major
Doctor of Philosophy
Christopher F Bauer
Understanding how students construct knowledge of pH buffer concepts is essential to developing effective instructional strategies to support student learning. A resource theoretical framework and the phenomenographic method were used to explore 12 general chemistry students’ conceptions of pH buffers using three buffer questions ranging from algorithmic to conceptual. Open coding of student responses revealed a diverse array of resources that varied in productivity and connectedness. A layered resource graph was introduced to visually compare resource activations across question contexts, highlighting some resources as important for all sensemaking about pH buffers, while others were specific to particular topics. The phenomenographic outcome space included three levels of resource activation: reliance on surface features; building connections between resources; and a knowledge structure that is interconnected. Students with the most interconnected resource structures were more likely to demonstrate an accurate understanding of buffer concepts. Therefore, promotion of productive and connected resources was hypothesized as a strategy to promote student learning. A laboratory activity was designed to promote activation of productive resources for buffer composition and how buffers work. Twelve groups of general chemistry students (25 students) investigated pH changes of an acetic acid–acetate buffer and an acetic acid non-buffer solution upon addition of strong base and completed associated worksheets. Promotion of the conjugate resource was successful during the laboratory activity itself. However, stability of resources over time was a challenge since less than half of the groups activated the conjugate resource when responding to the post-question on preparation of a buffer. In addition, targeting several concepts of pH buffers in one session as well as comparing four complex equilibria calculations caused significant strain on working memory and shifted students to a mathematical epistemology rather than chemical sensemaking. The intent to target the equilibrium resource was not successful since only two students showed an improved use of equilibrium in their explanation of how buffers work. Nonetheless, analysis of students’ responses led to the identification of dissociation and covariational reasoning as key gateway resources for understanding pH buffer concepts, knowledge that was incorporated into the next intervention. Backward design and visuospatial thinking were used to create a graphical visualization activity to promote activation of productive resources for choosing buffer components. To prevent cognitive overload, simple-to-complex sequencing was used to show pH and concentration changes of a buffer exemplar solution and two non-buffer solutions upon addition of strong acid and base. Inclusion of an explicit statement on ionic solution behavior promoted productive activation of the dissociation resource. Comparison of pre- and post-responses for a preparation of a buffer question revealed that nine of 13 students had an increase in their level of resource activation. Moreover, nine students productively activated the conjugate resource in the post-question compared to zero students in the pre-question. Resource maps were created to visualize the chronology of students’ resource activation pathways throughout the activity. Students’ maps showed that the graphical representations were effective at promoting productive resources that generally stayed activated during the post-question response. However, structural similarity was observed to be a superficial resource activated by students who did not have stable resource structures involving a relationship between pH, pKa, and conjugate pairs. Overall, the graphical teaching strategy was effective in promoting productive resources and improving student understanding of how to choose buffer components at a particular pH.
Sheppard, Mary Alice Woodland, "Investigation and Enhancement of Students’ Conceptions of pH Buffers" (2023). Doctoral Dissertations. 2766.
Available for download on Thursday, June 26, 2025