conjugate acid-base pairs - HX + H2O >> X- + H3O+  

• HX is acid
  • conjugate acid of X- (add proton)
• H2O acts as base
  • conjugate base of H3O+ (subtract proton)
• X- is base
  • conjugate base of HX (subtract proton)
• H3O+ acts as acid
  • conjugate acid of H2O (add proton)
• conjugate acid of strong base = weak acid
• conjugate acid of weak base = strong acid
• conjugate base of strong acid = weak base
• conjugate base of weak acid = strong base
• Ka x Kb = Kw
  • Kw = 1.0 x 10-14 (water autoionizes)
  • Ka = Kb >> neutral solution

Find the pH for 0.25 M of sodium lactate  

• conjugate acid is lactic acid
• Ka of lactic acid = 1.4 x 10-4
• Kb = Kw / Ka = 10-14 / (1.4 x 10-4) = 7.14 x 10-11
• Kb = [OH-] [lactic acid] / [lactate]
• [OH-] = [(7.14 x 10-11) (0.25)]1/2 = 4.2 x 10-6
• pOH = -log [OH-] = 5.37
• pH = 14 - 5.37 = 8.63

hydrolysis - ability of ions to react w/ water to make H+, OH- ions  

• anions act as bases (adding proton >> acid)
  • identify conjugate acid, use Kw to find the strength
  • anions of strong acids have negligible effect
  • anions of weak acids increase pH
• cations act as acids (subtract proton >> base)
  • identify conjugate base, use Kw to find the strength
  • cations of strong bases have negligible effect
  • cations of weak bases decrease pH