08-Jun-2012

Knowledge Statements

1. A solution is a stable homogenous mixture of two or more components; it will not become “unmixed” over time.
2. For a solute to dissolve in a solvent, the Gibbs Energy change must be negative.
3. The factors that effect solubility are the enthalpy change which is due to changes in solute-solute, solute-solvent, and solvent-solvent molecular level interactions and the entropy change, which arises from changes in the number of available states.
4. When a solution forms and the temperature increases (and exothermic reaction), this is because more stable interactions are being formed between solute and solvent. The entropy change cannot be predicted from this observation.
5. When a solution forms and the temperature decreases (and endothermic reaction), this is because the interactions between the solute and solvent are less stable than the original solute-solute and solvent-solvent interactions. In this case the entropy change must be positive since ΔG is negative.
6. The common rule of thumb of “like dissolves like” completely ignores entrophic effects (which is often critical). 

Performance expectations:

• Interconvert between mass, moles, molarity (M), and volume for both molecular and ionic species.
• Draw the structure of molecules in solution (include solvent).
• Explain why temperature changes when a solution forms, in terms of the interactions that are broken and formed during the solution process (i.e. enthalic effects).
• Describe the solution process in terms of entropy changes for both solute and solvent.
• Construct models that explain how amphipathic molecules self-organize in water, including structural, energetic, and entropic factors involved.
• Explain the factors that lead to colloid and emulsion formation, rather than the formation of a “simple” solution.