This study explored elementary pre-service teachers' content knowledge for dissolving before and after an instructional intervention over a 15-week science methods course. Pre-service teacher knowledge was examined using pre/post concept maps (Cmaps) and drawings with narrative descriptions. A mixed methods approach was used for both data collection and analysis. All data were thematically analyzed and a paired t-test was conducted on all collected pre- and post- Cmaps. Results of the study showed that prior to the study, pre-Cmap data indicated that participants held misconceptions and scientific conceptions, while post-Cmap data revealed an 86% improvement in knowledge with substantial gains for scientific concepts (e.g., rate, reversibility, solutes/solvents, solution, and homogeneous distribution of particles). The t-test showed statistically significant differences between pre/post Cmap scores (t = -5.071, p < 0.001) with the instructional intervention larger for post-Cmap scores (M = 3.58; SD = 2.561) than for pre-Cmap scores (M = 0.67; SD = 1.278). The effect size was very large. Analysis of drawings and narratives demonstrated knowledge of the hydration shell structure and the concept that dissolving is a reversible process (76%). This study suggests that pre-service teachers may possess a mosaic of conceptual understanding that is not scientifically valid and that significant remediation through concrete learning experiences may be required to elevate prior knowledge before introducing abstract concepts.