Strong vs Weak
| Property | Strong | Weak |
|---|---|---|
| Dissociation | Complete (→) | Partial (⇌) |
| pH (same conc) | Lower (more acidic) | Higher |
| Conductivity | Higher (more ions) | Lower |
| Examples (acid) | HCl, HNO₃, H₂SO₄ | CH₃COOH, H₂CO₃ |
The pH Scale
Ka — Acid Dissociation Constant (HL)
For a weak acid HA: \( K_a = \frac{[\text{H}^+][\text{A}^-]}{[\text{HA}]} \)
Large Ka = stronger weak acid. \( pK_a = -\log K_a \) (small pKa = stronger acid)
Think About It
0.1 mol dm⁻³ HCl and 0.1 mol dm⁻³ CH₃COOH — both are 0.1 M acids. Why do they have different pH values?
HCl fully dissociates → [H⁺] = 0.1 M → pH = 1. CH₃COOH only partially dissociates → [H⁺] < 0.1 M → pH > 1 (typically ~2.9). Same concentration but different degrees of dissociation.