Chapter 16: Acid-Base Equilibria

Definitions of Acids and Bases

• Arrhenius:
  • Acid: Increases concentration of H₃O⁺ in water.
  • Base: Increases concentration of OH⁻ in water.
• Brønsted-Lowry:
  • Acid: Proton (H⁺) donor.
  • Base: Proton acceptor.
• Lewis:
  • Acid: Electron pair acceptor.
  • Base: Electron pair donor.

Brønsted-Lowry Acids and Bases

• Acids must have a removable H⁺.
• Bases must have a lone pair of electrons.

Water as a Proton Acceptor

• H⁺ ions in water form H₃O⁺ stabilized by hydrogen bonding.

Amphiprotic Substances

• Can act as both acid and base.
• Water can donate or accept H⁺.

Lewis Acids and Bases

• All Brønsted-Lowry acids/bases are also Lewis acids/bases.
• Proton acceptors require an unshared electron pair.

Conjugate Acid-Base Pairs

• An acid and a base differing by H⁺ are conjugate pairs.
• Acid-base reactions yield conjugate acids and bases.

Relative Strengths of Acids and Bases

• Strong acids donate protons easily; weak acids do not.
• Inverse relationship: stronger the acid, weaker the conjugate base, and vice versa.

Acid-Base Equilibrium

• Equilibrium favors proton transfer from stronger acid to stronger base.

Autoionization of Water

• Water can act as both acid and base.
• Ion product constant for water: Kw = 1.0 x 10⁻¹⁴.

The pH Scale

• pH reports hydrogen ion concentration.
• Neutral: pH = 7, Acidic: pH < 7, Basic: pH > 7.
• pKa indicates acid strength: lower pKa, stronger acid.

Strong Acids and Bases

• Strong acids dissociate completely in water.
• Strong bases include soluble hydroxides of alkali metals and some alkaline earth metals.

Weak Acids and Bases

• Weak acids partially dissociate; characterized by Ka.
• Weak bases characterized by base-dissociation constant, Kb.

Calculating pH and pKa

• For weak acids: use ICE tables to calculate equilibrium concentrations and pH.
• Relationship between Ka and Kb for conjugate pairs: product is Kw.

Acid-Base Properties of Salts

• Salts can be acidic, basic, or neutral based on their ionization in water.
• Hydrolysis of anions or cations affects pH.

Acid-Base Behavior and Chemical Structure

• Factors affecting acid strength:
  • Bond polarity and strength.
  • Stability of the conjugate base.
• Binary Acids:
  • Within a group, bond strength is key.
  • Within a period, bond polarity is key.
• Oxyacids:
  • Acidity increases with electronegativity and number of O atoms.
• Carboxylic Acids:
  • Acidity influenced by electron-withdrawing effects and resonance stabilization.