Example: HClO4 [O3Cl(OH)] is very acidic NaOH is very basic Acid strength also increases with DECREASING radii of the “central atom” Example: HOCl (bond between Cl and OH is covalent acidic) – HOI (bond between I and OH is ionic basic) – 12. Acid Ionization Constant (Ka): HA + H2O H3O+ + A- Example: HF + H2O H3O+ + F- What is the pH of 0.5 HCN solution for which = 6.2 × 10-10? M Ka 13. Base Ionization Constant (Kb): B + H2O BH+ + Example: F- + H2O HF + What is the pH of a 0.5 NH2OH solution for which = 6.6 × 10-9? M Kb Do equal number of and problems as they are equally likely! Ka Kb 14. × = = 10-14 Ka Kb Kw ONLY applies for conjugate acids and bases at 25 oC! 15. Percent ionization = [H+]equilibrium / [HA]initial × 100 16. Lewis Acids and Bases: Lewis acid electron pair acceptor – Lewis bases electron pair donor – In complex ions formation, metal ions are Lewis acids, and ligands are Lewis bases. Example: Cu2+ + 4 NH3 [Cu(NH3)4]2+ Cu2+ acts as an acid; NH3 acts as a base 17. Buffers: Similar concentrations of a weak acid and its conjugate base -or- Similar concentrations of a weak base and its conjugate acid If these concentrations are large in comparison to SMALL amounts of added acid or base, equilibrium will be shifted slightly and the pH change resisted. Consider: HA H+ + A-
Example: HClO4 [O3Cl(OH)] is very acidic NaOH is very basic Acid strength also increases with DECREASING radii of the “central atom” Example: HOCl (bond between Cl and OH is covalent – acidic) HOI (bond between I and OH is ionic – basic) 12. Acid Ionization Constant (Ka): HA + H2O H3O+ + A- Example: HF + H2O H3O+ + F- What is the pH of 0.5 M HCN solution for which Ka = 6.2 × 10-10? 13. Base Ionization Constant (Kb): B + H2O BH+ + Example: F- + H2O HF + What is the pH of a 0.5 M NH2OH solution for which Kb = 6.6 × 10-9? Do equal number of Ka and Kb problems as they are equally likely! 14. Ka × Kb = Kw = 10-14 ONLY applies for conjugate acids and bases at 25 oC! 15. Percent ionization = [H+]equilibrium / [HA]initial × 100 16. Lewis Acids and Bases: Lewis acid – electron pair acceptor Lewis bases – electron pair donor In complex ions formation, metal ions are Lewis acids, and ligands are Lewis bases. Example: Cu2+ + 4 NH3 [Cu(NH3)4]2+ Cu2+ acts as an acid; NH3 acts as a base 17. Buffers: Similar concentrations of a weak acid and its conjugate base -or- Similar concentrations of a weak base and its conjugate acid If these concentrations are large in comparison to SMALL amounts of added acid or base, equilibrium will be shifted slightly and the pH change resisted. Consider: HA H+ + A-
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