Scientific behavior is characterized by the construction of explanations and this process takes a central role in the advancement of science and technology. The US Next Generation Science Standards posit the construction of explanations as one of eight science practices that are essential for all students to learn. To produce sound scientific explanations, skills associated with scientific behavior (e.g., analytical reasoning and critical thinking) must come into play to generate causal relationships between empirical evidence (e.g., experimental data) and theories (e.g., chemistry concepts). Research on science learning voiced the need to design activities that support scientific skill development to improve student’s skillset. The work herein presents a learning experience centralized on the construction of explanations designed for chemistry teaching laboratories. In the lab, students studied two ternary systems and their equilibrium state when the chemicals were mixed. The two systems were water-acetone-hexane and K2CO3-water-isopropanol. For both systems, it was found that the value of the equilibrium constant (Kd) changed when the initial masses of all species were changed. That is, the Kd was affected by the total number of molecules of each species present in the mixture. This result was not expected by students, thus they needed to construct an explanation for these empirical data. To understand the dependency of Kd with the composition of the total mixture, students then studied the effect of temperature on the equilibrium via the van’t Hoff isochore equation using different mass mixtures. Findings from these studies allowed for the determination of the ΔH and ΔS of the processes. With the values of ΔH and ΔS, students then worked on building causal relationships in regards to the intermolecular interactions and the changes in molar volume leading to the establishment of the equilibrium state. Examples of the procedures, data, and results will be presented and discussed to showcase their future implementation in teaching laboratories.

Constructing evidence-based chemical explanations in the lab via causal relationships between equilibrium constants and molecular interactions

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.