1. Section 13.2 and 13.3 Control of Solubility Bill Vining SUNY Oneonta

2. Control of Solubility In these sections… Molecular structure (inherent) control: a.Entropy and thermodynamic control b.Gas mixtures c.Mixtures of neutral molecules in liquids d.Mixtures of ionic compounds in water External (conditions) control: a.pressure b.temperature

3. Enthalpy and Entropy Enthalpy,  H : Bond strength- stronger bonds = lower enthalpy = more stable Entropy,  S : Free motion of atoms- freer mobility = higher entropy = more stable

4. Example: Enthalpy and Entropy of Evaporation

5. Enthalpy and Entropy Control of Dissolution

6. Gas Mixtures

7. Liquid-Liquid Mixtures

8. Predicting Miscibility of Two Liquids General rules: 1. polar solutes dissolve in polar solvents 2. nonpolar solutes dissolve in nonpolar solvents “Like dissolves Like” Oil and water don’t mix: is oil polar or nonpolar? For now, we are examining molecular compounds- not ionic compounds.

9. Hydrophilic groups: Hydrophobic groups: –OH and –NH groups Examples: CH 3 OH, NH3, H-O-O-H Long hydrocarbon groups: CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 Examples: CH 3 CH 2 CH 2 CH 2 CH 3 CH 3 CH 2 CH 2 CH 2 Cl

10. Which of these will not dissolve in water? 1.NH 3 2.CH 3 CH 3 3.CH 3 OH

11. Which of these is least soluble in water? 1.CH 3 OH 2.CH 3 CH 2 CH 2 OH 3.CH 3 CH 2 CH 2 CH 2 OH

12. Why don’t oil and water mix? What controls Solubility: Enthalpy (enthalpy of solution) Negative if new forces are stronger than original forces Entropy Depends on the entropy change of both the water and the solute.

13. Assume they mix fully

14. Assume water retains its hydrogen bonds

15. Which is it? “Do the experiment.” Experiments show mixing water and oil has:  H close to zero  S highly negative

16. Why do Proteins Fold?

18. Without lipids, you’d fall apart.

19. What holds DNA together?

20. Laundry!

23. Control of Solubility of Ionic Compounds

25. Enthalpy Control Entropy Control

26. Control of Solubility of Ionic Compounds Enthalpy: lattice energies and hydration energies follow same trends and mostly offset Entropy: smaller ions and ions of high charge have larger hydration spheres and are entropy disfavored from dissolving

27. Control of Solubility of Ionic Compounds

28. External Control of Solubility Pressure Effects : Solubility of Gases in Liquids As P of a gas increases, its solubility increases. Henry’s Law: What is the solubility of O 2 under a pressure of 0.66 atm?

29. External Control of Solubility Temperature Effects In general, if  H dissolution is exothermic, solubility decreases as temperature increases

30. In general, but not always: if  H dissolution is exothermic, solubility decreases as temperature increases if  H dissolution is endothermic, solubility increases as temperature increases What do we expect for ammonium nitrate? NH 4 Cl(s)  NH 4 Cl(aq)  H o = +14.8 kJ/mol KCl(s)  KCl(aq)  H o = +17.2 kJ/mol Li 2 SO 4 (s)  Li 2 SO 4 (aq)  H o = -29.8 kJ/mol But: LiCl(s)  LiCl (aq)  H o = -37.0 kJ/mol