This study aims to determine the cognitive structures of students at different educational levels (8th grade and 12th grade) related to acid-base chemistry. The research was designed as a case study and structured in two stages. The first stage analyzed concepts related to acid-base chemistry and their direction and strength in students' knowledge structures. The second stage determined the descriptive and structural features of students' knowledge structures related to acid-base chemistry in a more holistic approach. The study was carried out with a total of 160 students, 80 grade 8th and 80 12th grade students. A word association test (WAT) and the free writing technique (FWT) were used together. In the WAT, ten different frequency ranges were determined forming cognitive structure maps of the students. With high-frequency values on the map, it was found that the number of stimulus and response words decreased but the strength of associations increased. In frequency ranges where the frequency values of associations were low, it was found that the number of stimulus and response words increased and the cognitive structure organization was at the most advanced level compared to other frequency ranges, but the strength of associations was weak. In general, it was observed that there were no bidirectional and cross-associations between the concepts in the cognitive structures of the students about chemistry and that there was a static structure that included one-way associations only. Additionally, the concepts in the cognitive structures of students related to acid-base chemistry were analyzed in terms of their structural characteristics. It was found that, in the cognitive structures of the students there were no associations between many concepts that should be related to each other.