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Section 13.2 and 13.3 Control of Solubility

Section 13.2 and 13.3 Control of Solubility. Bill Vining SUNY Oneonta. In these sections… Molecular structure control: Entropy and thermodynamic control Gas mixtures Mixtures of neutral molecules in liquids Mixtures of ionic compounds in water External (conditions) control: pressure

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Section 13.2 and 13.3 Control of Solubility

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

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

  3. Enthalpy and Entropy Enthalpy: Bond strength- stronger bonds = lower enthalpy = more stable Entropy: 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 For now, we are examining molecular compounds- not ionic compounds. 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?

  9. Hydrophilic groups:Hydrophobic groups: –OH and –NH groups Examples: CH3OH, NH3, H-O-O-H Long hydrocarbon groups: CH3CH2CH2CH2CH2CH2 Examples: CH3CH2CH2CH2CH3 CH3CH2CH2CH2Cl

  10. Which of these will not dissolve in water? • NH3 • CH3CH3 • CH3OH

  11. Which of these is least soluble in water? • CH3OH • CH3CH2CH2OH • CH3CH2CH2CH2OH

  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? • Experiments show mixing water and oil has: • H close to zero • S highly negative

  16. Control of Solubility of Ionic Compounds

  17. Control of Solubility of Ionic Compounds

  18. Enthalpy Control Entropy Control

  19. 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

  20. Control of Solubility of Ionic Compounds

  21. 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 O2 under a pressure of 0.66 atm?

  22. External Control of Solubility • Temperature Effects • In general, • if Hdissolution is exothermic, solubility decreases as temperature increases • if Hdissolution is exothermic, solubility decreases as temperature increases

  23. In general, but not always: • if Hdissolution is exothermic, solubility decreases as temperature increases • if Hdissolution is endothermic, solubility increases as temperature increases What do we expect for ammonium nitrate?

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