8.6 Molecular Structure of Acids and Bases

Explain the relationship between the strength of an acid or base and the structure of the molecule or ion.

• The protons on a molecule that will participate in acid-base reactions, and the relative strength of these protons, can be inferred from the molecular structure.
  • i. Strong acids (such as HCl, HBr, HI, HClO4, H2SO4, and HNO3) have very weak conjugate bases that are stabilized by electronegativity, inductive effects, resonance, or some combination thereof.
  • ii. Carboxylic acids are one common class of weak acid.
  • iii. Strong bases (such as group I and II hydroxides) have very weak conjugate acids.
  • iv. Common weak bases include nitrogenous bases such as ammonia as well as carboxylate ions.
  • v. Electronegative elements tend to stabilize the conjugate base relative to the conjugate acid, and so increase acid strength.