1. 1 Properties of Solutions Brown, LeMay Ch 13 AP Chemistry CaCl 2 (aq)

2. 2 13.1: Types of Solutions ExampleSolventSolute Air (g in g) Soda (g in l) H 2 in Pt (g in s) Alcoholic beverages (l in l) Sea water (s in l) Brass (s in s) N2N2 O2O2 H2OH2OCO 2 PtH2H2 H2OH2OC 2 H 5 OH H2OH2O NaCl (one of many salts) Copper (55% – 90%) Zinc (10% – 45%)

3. 3 When do solutions form? Solutions form (the solute and solvent will mix) when: Energy: solute-solvent interactions are stronger than solute-solute or solvent-solvent interactions. Disorder: Solutions result in a more disordered state than the separate solute and solvent states, since molecules will be “mixed” that were once “well organized”. NaCl (s) + H 2 O (l) → Na + (aq) + Cl - (aq) Ion-dipole interactions > H-bonds (H 2 O···H 2 O) < Ionic bonds (Na + Cl - ) The increase in disorder also drives the dissolving process.

4. 4 13.2: Ways to Express Concentration Mass Percent Mole Fraction: commonly used for gases Molarity: commonly used for solutions Molality: commonly used for colligative properties Does not vary with T Varies with T

5. 5 13.3: Solubility Vocabulary Solvation: dissolving; the interactions between solute and solvent Hydration: solvation with water Crystallization: “un-dissolving”; process by which solute particles leave the solvent. Solute + solvent ↔ solution (equilibrium)

6. 6 13.3: Solubility Vocabulary Saturated: a solution that is in equilibrium with undissolved solute (appears as solution and crystals) Solubility: the amount of solute needed to form a saturated solution Unsaturated: a solution containing less than the saturated amount (appears as solution only) Supersaturated: a solution containing more than the saturated amount, yet appears unsaturated.

7. 7 13.4: Factors Affecting Solubility 1.“Like dissolves like.” Miscible: liquids that mix (polar or ionic solute with polar solvent, or nonpolar with nonpolar) Immiscible: liquids that do not mix (polar or ionic solute with nonpolar solvent) Covalent network solids do not dissolve in polar or nonpolar solvents.

8. 8 13.4: Factors Affecting Solubility 2.Pressure: does not significantly affect solubility of liquids and solids Gases: increased P means increased solubility Henry’s law: C g = k P g C g = solubility of gas in solution (M) k = Henry’s law constant P g = partial pressure of gas over solution William Henry (1775-1836)

9. 9 13.4: Factors Affecting Solubility 3.Temperature Most solids: increased T means increased solubility * Exception: Ce 2 (SO 4 ) 3 Gases: increased T means decreased solubility

10. 10 13.5: Colligative Properties Properties that are dependent on the number of solute particles present in solution 1.Vapor pressure lowering: the greater the concentration of a nonvolatile solute, the lower the vapor pressure of the solvent Solute takes up surface area Introduction of solute-solvent IMF Raoult’s law: P A = X A P° A P A = vapor pressure of solvent vapor above solution (solute A is nonvolatile) X A = mole fraction of solute A P° A = normal vapor pressure of solvent François- Marie Raoult (1830-1901)

11. 11 Ideal solution: described by Raoult’s law Has low concentration of solute Solute and solvent have similar types of IMF & molecular sizes

12. 12 Extension of the Liquid Phase 2.Boiling point elevation:  T b = i K b mK b (H 2 O) = 0.51 ºCkg/mol 3.Freezing point depression:  T f = i K f mK f (H 2 O) = 1.86 ºCkg/mol  i = van’t Hoff factor: Unitless constant associated with the degree of dissociation of a solute in a solvent Jacobus van’t Hoff (1852-1911)

13. 13 Ideal i values i = 1Substances which do not ionize in solution Ex: sucrose (sugar) i = 2Substances which ionize into 2 ions Ex: NaCl i = 3Substances which ionize into 3 ions Ex: MgCl 2 Ex: Determine the solute “equivalent molality” (factoring in i) for the following solutions: 1-m sucrose 1-m NaCl 1-m CaCl 2

14. 14 Osmotic Pressure (  ) 4.Pressure required to prevent osmosis of solute particles Applied on solution side to stop net movement of solvent from the pure solvent side. Osmosis: net movement of solvent toward the solution with the highest solute concentration  = iMRT = (n/V)RT R = 0.0821 L-atm/mol-K Prevents flow of solute particles Solvent “wants” to flow 

15. 15 13.6: Colloids Mixtures containing particles intermediate between: A solution (homogeneous, < 10 Å) and A suspension (heterogeneous, > 2000 Å) Tyndall effect: scattering of light seen in a colloid John Tyndall (1820-1893)