This study investigated the quality of content knowledge (CK) held by Grade 12 Physical Sciences teachers regarding acids and bases, a critical component of the South African Curriculum and Assessment Policy Statement (CAPS). The investigation was motivated by persistent concerns over poor learner performance in Physical Sciences, which has been linked to inadequate teacher content knowledge. National Diagnostic Reports from 2015 to 2024 consistently indicate underachievement in questions relating to acids and bases, with the average national performance for related items often below 50%. Against this background, this study sought to determine the quality of CK among teachers currently teaching the topic in Johannesburg Metropolitan District high schools.

Using a survey research design, data were collected from 18 grade 12 physical sciences teachers who were purposively sampled, each meeting specific inclusion criteria: qualified to teach at the FET level, currently teaching grade 12, and with at least three years of experience teaching acids and bases at the grade 12 level. A CK questionnaire, whose design was informed by the Grade 12 CAPS Physical Sciences curriculum, was administered. The CK questionnaire consisted of multiple-choice and open-ended items designed to assess teachers’ understanding across symbolic, macroscopic, and microscopic levels of science representation.

The findings indicate that only 33.3% of the teachers met the benchmark score of 80%, which was set as the threshold for good CK. Qualitative and statistical analyses revealed specific challenges, including confusion between the Arrhenius and Brønsted–Lowry theories, a shallow understanding of acid-base reactions and pH calculations, and difficulty articulating scientific reasoning with clarity. Notably, some participants displayed good conceptual understanding when responding to diagrammatic representations (macroscopic level) but struggled to articulate this understanding in written form, indicating potential language proficiency barriers. Conversely, others succeeded in providing symbolic explanations but failed to interpret diagrams correctly, highlighting fragmented content understanding.

The findings underscore that some teachers possess a surface-level or compartmentalized grasp of core concepts in acids and bases, which may inhibit their ability to teach the topic effectively in the future. Given the pivotal role of teacher CK in shaping learner performance, these deficits have serious implications for curriculum delivery and learner success in Physical Sciences. The study recommends ongoing professional development targeting conceptual depth and pedagogical clarity, particularly for scientifically dense topics such as acids and bases. Furthermore, this suggests the need for integrating strategies to enhance language-in-science instruction, which may help address the issues of clarity and articulation observed in open-ended responses.

This research contributes to the discourse on teacher content knowledge as a determinant of educational quality and highlights the urgent need to support teachers in strengthening their CK to foster improved learner performance in Physical Sciences.

Keywords: Content knowledge, acids and bases, physical sciences education, CAPS curriculum.