Session S26d (Wednesday, 9:30am, Thomas 117)

P723: Inquiry-based module for teaching about solubility in general chemistry

Laura Eisen (George Washington University, USA)

The generalization “like dissolves like” is traditionally rationalized in terms of energy interactions.  However, enthalpy changes alone cannot always explain why polar and ionic substances dissolve in water, or why non-polar substances do not.   Furthermore, many ionic compounds are not appreciably soluble in water, yet most textbooks do not 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 utilizes 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.


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