This paper discusses metacognition, defined as thinking about one's own thinking, and its role in conceptual change and problem solving in chemistry. Educational research shows that promoting metacognition in the science classroom prompts students to refine their ideas about scientific concepts and improves their problem-solving success. Examples of how metacognition affects problem-solving success are presented, some instructional tools that have been employed to promote metacognition in introductory science courses are discussed, and possible directions for research on metacognition and learning in chemistry are proposed.

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In the studies reported here, we investigate the effects of context on students' molecular-level ideas regarding aqueous solutions. During one-on-one interviews, 19 general chemistry students recruited from a two-year community college and a research university in the United States were asked to describe their molecular-level ideas about various aqueous solutions in the contexts of conductivity and boiling-point (BP) elevation. Results indicate that context is important for determining the molecular-level ideas that students express. Specifically, students were significantly more likely to draw pictures of aqueous NaCl as separated ions in the conductivity context compared with the BP elevation context, for which they more often drew "molecular" NaCl. This phenomenon was particularly striking because the students drew molecular-level NaCl(aq) pictures in the BP elevation context just minutes after completing the identical task in the context of conductivity. Additional data from laboratory assignments and course examinations further indicate that, even if students are able to correctly represent the molecular level in some contexts, their knowledge may remain inert in slightly different contexts. The results emphasise the importance of the context dependence of molecular-level ideas and have implications for designing instruction in which students develop robust, coherent understandings that they can apply appropriately in new contexts.

This article describes a laboratory module designed to help students understand how different compounds behave when they are dissolved in water. Students measure the conductivities of various aqueous solutions using handheld conductivity testers with LED displays. By counting the number of LEDs illuminated, students can differentiate between electrolytes and nonelectrolytes and approximate the relative numbers of ions in solution. This enables students to discover how ionic compounds dissociate when dissolved in water. The laboratory module introduces the model–observe–reflect–explain (MORE) thinking frame, an instructional tool that encourages students to connect their macroscopic observations with their understanding of the behavior of particles at the molecular level. These activities are designed for college-level general chemistry courses, but have also been adapted to the high-school level.

Metacognitive monitoring of one's own understanding plays a key role in learning. An aspect of metacognitive monitoring can be measured by comparing a student's prediction or postdiction of performance (a judgment made before or after completing the relevant task) with the student's actual performance. In this study, we investigated students' postdiction accuracies for a series of exams within a twosemester general chemistry course. The research questions addressed include (1) How accurate are general chemistry students at postdicting their exam scores? Are there gender differences in postdiction accuracy?(2) How do general chemistry students' postdiction accuracies relate to their exam performance? (3) How do general chemistry students' postdiction accuracies and metacognitive monitoring of their exam performance change over time? Results indicate that most general chemistry students are not accurate in their exam score postdictions and that, consistent with research conducted in other domains, higher-performing students make more accurate postdictions than lower-performing students. In addition, although students who were new to a general chemistry course appeared to improve in their metacognitive monitoring on the second course exam compared with the first, monitoring did not significantly improve after that initial adjustment. Given the importance of metacognitive monitoring for student learning of chemistry, these findings suggest that further research and development of interventions to improve the metacognitive monitoring of introductory chemistry students is warranted.