Acid/Base Equilibria

• Bronsted-Lowry Acid


  Proton donor (H+)
• Bronsted-Lowry Base


  Proton acceptor
• Lewis Acid


  Electron pair Acceptor
• Lewis Base

  Electron pair donor
• Buffer


  An aqueous solution that resist changes in pH when added to an acid or base
• Buffers


  • Weak acid with conjugate base
  • Weak base with conjugate acid
• Phosphate buffer


  Commonly used buffer
• Ka


  Acid ionization constant/ acid dissociation constant
• Weak acid equilibrium

  • HF (hydrofluoric acid): Ka= 3.5 x 10^-4
  • CH3COOH (acetic acid): Ka= 1.8 x 10^-5
  • CH3OH (methanol): Ka= 2.9 x 10^-16
• Weak base equilibrium

  • NH3 (Ammonia): Kb= 1.8 x 10^-5
  • C6H5NH2 (Aniline): Kb= 4.3 x 10^-10
• Ka x Kb

  Always equal Kw
• Stronger/higher Kb


  The weaker Kb
• pKa + pKb

  = 14
• Neutral salt solution


  Neither the cation or anion will react in water or solution
• Neutral salt solutions

  • Ba(NO3)2
  • NaCl
• Basic salt solution


  The cation does not react in water, but the anion does
• Basic salt solutions

  • Ba(CH3COO)2
  • NaClO
• Acidic salt solution


  The cation will react with water but the anion will not react with water
• Acidic salt solutions

  • NH4NO3
  • AlCl3
• Acidic, Neutral, or Basic salt solution


  The cation and anion both interact with water
• Acidic, Neutral, or Basic salt solution


  • (NH4)2CO3
• Increasing the concentration of one of the products


  Shifts the equilibrium to the left
• the larger the Ka value= the stronger the acid
• the smaller the Ka value= the weaker the acid
• the larger the Kb value= the stronger the base
• the smaller the Kb value= the weaker the base