This study examines the nature and process of ninth grade students' conceptual change regarding their mental model of dissolution and diffusion as a result of instructions using the Dual Situated Learning Model (DSLM). The dual situated learning events of this model are designed according to the students' ontological viewpoint of the science concepts as well as the nature of these concepts. Moreover, these events serve two functions by creating dissonance with the pre-existing knowledge and providing new schema for constructing a more scientific view of the concept. The concepts of dissolution and diffusion were chosen to examine students' conceptual change process because they involve the understanding of both invisible and process attributes. Results indicate that about 76%-90% of the students successfully underwent a change in their understanding of the concepts of dissolution and diffusion after instruction using dual situated learning events. Moreover, about 75% of the students successfully applied their previous mental sets into the challenging situated learning event. This current study demonstrates that DSLM indeed facilitates the processes of conceptual change and knowledge acquisition involving concepts of dissolution and diffusion, clarifying the nature of conceptual change involving science concepts of both an invisible and a process nature.