Activity-Based Approach For Teaching Aqueous Solubility, Energy, and Entropy

Abstract

We describe an activity-based approach for teaching aqueous solubility to introductory chemistry students that provides a more balanced presentation of the roles of energy and entropy in dissolution than is found in most general chemistry textbooks. In the first few activities, students observe that polar substances dissolve in water, whereas nonpolar substances do not, and that in some cases, dissolution is endothermic. Because energy minimization alone cannot explain these observations, we introduce entropy descriptively as another factor promoting dissolution. The increase in entropy due to mixing can counteract unfavorable energy changes, whereas unfavorable entropy changes due to reorganization of the water explain why nonpolar substances do not dissolve. In another activity, students mix combinations of positive and negative ions and formulate a simple rule that predicts the solubility of most ionic compounds: salts in which the cations and anions are multiply charged are likely to be insoluble; other salts are likely to be soluble. Students later discover that the sign and magnitude of the entropy changes explain why the rule works so often. Salts that are exceptions to the rule generally have unusually large enthalpies of dissolution.

Identifying microbes from environment water samples in a discovery-based learning module

“…Accumulating evidence from education research indicates that inquiry-based exercises with practical experiential components (also known as active learning) are useful for increasing students' motivation towards learning and enhancing content mastery. [48][49][50][51][52][53][54] Specifically, acquisition of conceptual understanding and problem-solving skills often go beyond algorithmic exercises; for example, students need to feel a sense of challenge in working on an interesting problem, which would further motivate them to go the extra mile in thinking about various solution strategies. 51 Finally, casting a forward glance, the next generation of students would likely judge the quality of teaching and the education they received by yardsticks different from those of earlier eras.…”

Identifying microbes from environmental water samples in a discovery-based learning module

“…Accumulating evidence from educational research indicates that inquiry-based exercises with practical experiential components (which fall under the general category of active learning tools) are useful for increasing students' motivation towards learning and enhancing content mastery. [48][49][50][51][52][53][54] In particular, acquisition of conceptual understanding and problem-solving skills often go beyond algorithmic exercises; for example, students need to feel a sense of challenge in working on an interesting problem, which would motivate them to go the extra mile in thinking about various solution strategies. 51 Finally, casting a glance towards the future, the next generation of students would likely judge the quality of teaching and the education that they receive via yardsticks such as the extent of critical thinking and active learning incorporated in educational exercises (e.g., homework, laboratory classes, field work, etc.).…”

Factors affecting the solubility of ionic compounds

“…Empirical tables predicting the solubility of ionic compounds have been developed and are regularly published in introductory-level collegiate chemistry textbooks [2]. However, explaining the solubility of any given individual compound has proven very difficult [3].…”

“…Aqueous ionic solubility is another such example, and is actually intimately tied to the idea of the chemical bond [3]. There exist several explanations within general chemistry texts or online discussion boards as to why certain ionic compounds are soluble in water and why others are not in contradiction to the general solubility rules.…”

“…However, there lacks a systematic analysis of more fundamental properties such as the molecular volume and the intimately related charge density property even though such phenomena are known to permeate the underlying chemical physics of solvation [1,3,4]. In order to develop simple theoretical explanations for ionic solubility, this work produces the volumes for a number of typical ions from quantum chemical computations.…”