1. Energetics of the Solution Process

2. When a solute dissolves in a solvent… IMFs of solvent are disrupted IMFs of solute are disrupted IMFs between solute-solvent are created Which steps are endothermic? exothermic?

3. Time for an experiment… (Investigate This 2.2) ethanol, colorless liquid in vial urea, white crystals in vial H 2 O in pipet

4. Investigate This 2.2  Add water to urea until the vial is ~1/2 full. Recap the vial and swirl to dissolve. Does the solution become warm or cool?  Add water to ethanol until the vial is ~full, cap, and mix. What happens?

5. Does this describe ethanol dissolving? Urea dissolving? The diagram shows changes in the solute only.

6. Predicting Solubility (Investigate This 2.5) methanol CH 3 OH hexane CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 1-butanol CH 3 CH 2 CH 2 CH 2 OH Which solute is most soluble in water?

7. Polar Solute + Water methanol CH 3 OH Type of Solute- Solvent IMFs?

8. Non-Polar Solute + Water hexane CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 Type of Solute- Solvent IMFs?

9. 1-butanol CH 3 CH 2 CH 2 CH 2 OH Water + Solute with Polar/Non-Polar Regions Type of Solute- Solvent IMFs?

10. Dissolving of Ionic Compounds

11. Interactions Between Ions Magnitude of attraction E coulomb  q 1 q 2 /d small ions of big charge have largest attractive forces ~400-4000 kJ/mol (huge!) accounts for high melting/boiling points d ion of charge q 1 ion of charge q 2

12. So,why do ionic compounds dissolve at all? How can strong ion-ion forces be overcome?

13. Ion-Dipole Interactions Ions can interact with polar molecules (dipoles) Magnitude of attraction E coulomb  q 1 q 2 /d Increases with ion charge, dipole moment ~40-600 kJ/mole iondipole with partial charges d  - + 

14. Ion-Dipole Interactions Most important example is ion-water Na + + 6H 2 O    [Na(OH 2 ) 6 ] +  E = -397 kJ/mole

15. Ion-Dipole Interactions Overcome Ion-Ion Forces

16. Energy Changes for NaCl Dissolving in Water

17. Like Dissolves Like Type of Solute Polar Molecules Nonpolar Molecules Ionic compounds Soluble in polar solvents (water, methanol, acetone) nonpolar or slightly polar solvents (C 6 H 6, CCl 4, CHCCl 3 ) very polar solvents (water) Solute-Solvent IMF dipole-dipole or H-bonding dispersion or weak dipole- dipole attractions ion-dipole attractions