P634: Exploring the roles of energy and entropy in aqueous solubility: An activity-based approach
The generalization “like dissolves like” is traditionally rationalized in terms of energy. However, enthalpy changes alone cannot explain why polar and ionic substances generally dissolve in water and non-polar substances do not. Furthermore, many ionic compounds are not appreciably soluble in water, yet few textbooks explore why some salts dissolve and others do not. Instead, they simply present solubility rules for students to memorize. This presentation describes an inquiry-based module that uses hands-on activities and worksheets to help students understand solubility. For example, students observe what happens when pairs of ionic solutions are mixed, and then use their observations to construct a single solubility rule. This approach encourages them to think about solubility in terms of chemical structure. When they later examine the thermodynamic changes that take place during dissolution, students discover the importance of entropy in the solution process, and recognize what causes some common exceptions to their solubility rule.