Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)



First Advisor

Suazette Mooring

Second Advisor

Kathryn Grant

Third Advisor

Renee Schwartz


The acid ionization constant, Ka, is a fundamental acid-base equilibrium concept that is taught in US post-secondary general chemistry II and threaded through later chemistry courses as pKa. It is essential that students’ have prior knowledge of acid-base models, acid strength, equilibrium, and Ka to comprehend pKa fully. However, many students possess unstable and incoherent ideas regarding these topics. Therefore, more effective teaching strategies and assessments are needed to provide support for this network of linked concepts. Think-aloud interviews with twenty undergraduate students across general chemistry, organic chemistry, and biochemistry were used to investigate students’ explanations and reasoning about equilibrium and acid ionization constant. Students’ reasoning was examined through the lens of meaningful learning and the resources framework.

It was found that, with prompting, most students were able to define at least one acid-base model, generally the Bronsted-Lowry model. Students were placed into five levels of sophistication based on their reasoning about acid strength, equilibrium, Ka and pKa. Upper-level students were less coherent and stable than lower-level students for acid strength. Interestingly, most students were unable to define equilibrium for a reaction and had an incoherent understanding. A trend was observed for upper-level students to converge on describing equilibrium in terms of equal amounts. Furthermore, it was found that students did not attribute more than reversibility to a double-headed arrow. Approximately one-quarter of the students used the concept of Ka coherently in multiple contexts throughout the study; however, a trend of incoherency was observed for students in organic chemistry II. Most students did not utilize pKa beyond a mathematical entity involving Ka, without regard to the actual concept.

These findings suggest that instructors need to provide opportunities for students to make meaningful connections between Ka and pKa and the underlying prior knowledge that is required to understand this complex topic. Instructors need to provide clarity to students in the meaning of words and the symbols used in acid-base chemistry. Additionally, when conducting assessments, students need to be assessed in more than one context to assure comprehension.

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