Acids & Bases — pH, pKa, Buffers

Definitions:

Arrhenius: Acid produces H⁺; base produces OH⁻ in water

Brønsted-Lowry: Acid is proton donor; base is proton acceptor

Lewis: Acid accepts electron pair; base donates electron pair

pH scale:

pH = −log[H⁺]; pOH = −log[OH⁻]; pH + pOH = 14

pH < 7 = acidic; pH = 7 = neutral; pH > 7 = basic

Strong acids: HCl, HBr, HI, H₂SO₄, HNO₃, HClO₄ — dissociate completely

Strong bases: NaOH, KOH, Ca(OH)₂

Weak acids/bases: Partially dissociate; have Ka/Kb and pKa/pKb

Henderson-Hasselbalch equation:

pH = pKa + log([A⁻]/[HA])

At pH = pKa, [A⁻] = [HA] (half ionized)

Buffers: Weak acid + conjugate base; resist pH changes. Effective within ±1 pH unit of pKa. Blood is buffered at pH 7.4 by the bicarbonate system (H₂CO₃/HCO₃⁻).

Reference:

Wikipedia: Acid-Base Reaction

https://en.wikipedia.org/wiki/Acid%E2%80%93base_reaction