Basics of Acids and Bases

Identifying Acids and Bases

• Acids:
  • Typically have a hydrogen (H) in front (e.g., HCl, HF, acetic acid HC₂H₃O₂).
  • Positively charged hydrogen (H⁺).
• Bases:
  • Typically contain a hydroxide ion (OH⁻) (e.g., NaOH, KOH).
  • Negatively charged hydrogen (H⁻), often found next to metals.

Definitions of Acids and Bases

• Arrhenius Definition:
  • Acid: Releases H⁺ ions into solutions.
  • Base: Releases OH⁻ ions into solutions.
• Brønsted-Lowry Definition:
  • Acid: Proton donor.
  • Base: Proton acceptor.

Examples

• HCl in water:
  • HCl (acid) donates a proton to water, forming Cl⁻ (conjugate base) and H₃O⁺ (conjugate acid).
• Ammonia in water:
  • NH₃ (base) accepts a proton, forming NH₄⁺ (conjugate acid) and OH⁻ (conjugate base).

pH and pOH

• pH Scale:
  • Ranges typically from 0 to 14.
  • 7 is neutral; <7 is acidic; >7 is basic.
• Calculating pH:
  • pH = -log [H₃O⁺].
  • pOH = -log [OH⁻].
  • pH + pOH = 14 at 25°C.

Strong and Weak Acids/Bases

• Strong Acids (e.g., HCl, HBr, HI, HNO₃, H₂SO₄, HClO₄): Ionize completely.
• Weak Acids: Partially ionize.
  • Strong acids form strong electrolytes; weak acids form weak electrolytes.
• Strong Bases: Fully ionize (e.g., KOH, NaOH).
• Weak Bases: Partially ionize (e.g., ammonia, NH₄⁺).

Chemical Reactions

• Strong Acids in Water: Single arrow in reactions (complete ionization).
• Weak Acids/Bases in Water: Reversible reaction (equilibrium, double arrow).

Lewis Acids and Bases

• Lewis Acid: Electron pair acceptor.
• Lewis Base: Electron pair donor.

Amphoteric Substances

• Can act as an acid or base (e.g., water, H₂PO₄⁻).

Acid/Base Strength and Trends

• Oxyacids: More oxygen atoms generally mean stronger acid (e.g., H₂SO₄ > H₂SO₃).
• pKa and pKb:
  • pKa = -log Ka; pKb = -log Kb.
  • Stronger acids have lower pKa values.
  • Ka × Kb = Kw = 1.0 × 10⁻¹⁴ at 25°C.

Practical Problems

• Calculating pH, pOH, [H₃O⁺], [OH⁻], Ka, Kb, etc.

Conductivity

• Strong Acids/Bases: Strong electrolytes (conduct electricity well).
• Weak Acids/Bases: Weak electrolytes.

Reactivity

• Acids react with active metals to produce hydrogen gas.

Indicators

• Acids turn blue litmus paper red.
• Bases turn red litmus paper blue.

This summary covers the identification of acids and bases, their definitions, reactions, and properties, including the understanding of pH, conductivity, and practical applications in chemistry.