ACIDS AND BASES

• Acids


  Substances that produce hydrogen ions (H+) in aqueous solution
• Bases


  Substances that produce hydroxide ions (OH-) in aqueous solution
• Dissociation of HCl in water

  HCl (aq) → H+ (aq) + Cl- (aq)
• Dissociation of H+ in water

  H+ (aq) + H2O (l) → H3O+ (aq)
• Dissociation of NaOH in water

  NaOH (s) → Na+ (aq) + OH- (aq)
• Bronsted-Lowry definition of acids and bases

  Acid: Proton donor, Base: Proton acceptor
• Reaction of NH3 with water

  NH3 (aq) + H2O (l) ⇌ NH4+ (aq) + OH- (aq)
• Conjugate acid-base pair


  Acid and base formed from each other by the loss/gain of a proton
• Lewis definition of acids and bases

  Acid: Electron pair acceptor, Base: Electron pair donor
• Arrhenius, Bronsted-Lowry, and Lewis definitions


  Arrhenius is the most specific, Lewis is the most general
• CH 3 COOH (aq) + H 2 O (l) ⇌ CH 3 COO — (aq) + H 3 O + (aq)

  1. CH 3 COOH converted to CH 3 COO —

  2. CH 3 COOH is a Bronsted-Lowry acid, CH 3 COO — is its conjugate base

  3. H 2 O acts as a base, H 3 O + is its conjugate acid
• CN — (aq) + H 2 O (l) ⇌ HCN (aq) + — OH (aq)


  1. CN — converted to HCN

  2. CN — acts as a base, HCN is its conjugate acid

  3. H 2 O acts as an acid, — OH is its conjugate base
• Strong acids and bases

  Dissociate completely in water
• Weak acids and bases


  Dissociate partially
• Strong bases


  • Hydroxides of Group I and Group II in the periodic table
• Strong acids


  • HCl, HBr, HI, HNO3, H2SO4 (first dissociation only), HClO4
• Dissociation of strong acids and bases

  Uses a unidirectional arrow as the reaction goes to completion
• Dissociation of weak acids and bases

  Uses bidirectional harpoons to signify the reaction is reversible and does not go to completion
• HCl (aq) + H 2 O (l) → Cl — (aq) + H 3 O + (aq)

  Strong acid in water
• CH 3 COOH (aq) + H 2 O (l) ⇌ CH 3 COO — (aq) + H 3 O + (aq)

  Weak acid in water