pKb from Base Dissociation Constant
Worked example: Methylamine Kb = 4.4e-4 → pKb = 3.35655 — press Try an example to run it live, then adjust anything.
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pKb from Base Dissociation Constant explained
Kb measures how far a base pulls a proton off water, and taking its negative logarithm produces the same compact scale that pKa gives on the acid side: small pKb means a strong base. Methylamine, with Kb = 4.4 × 10⁻⁴, has pKb = 3.36 and is a distinctly stronger base than ammonia at Kb = 1.8 × 10⁻⁵ and pKb 4.74 — the extra electron density from the methyl group is worth more than a full order of magnitude.
Modern practice increasingly skips pKb entirely and quotes the pKa of the conjugate acid instead, since a single acid scale ranks everything from sulfuric acid to hydroxide without ever switching frameworks. The two are locked together by pKa + pKb = 14 at 25 °C, so a base of pKb 9.25 has a conjugate acid of pKa 4.75. Just remember that identity, like pH + pOH = 14, holds only near room temperature: Kw climbs with heat, and at 60 °C the sum is closer to 13.0.
pKb from Base Dissociation Constant formula
- = pKb
- = Base dissociation constant
Missing one of these? Work it out first, then come back
- Base dissociation constant — Ka and Kb Relation through Kw, pKa from Acid Dissociation Constant
Acid–base relations
7 formulaspH, pOH, Kw, Ka and Kb and the weak-acid shortcut — the chain that turns a concentration into a pH and back again.
The buffer equations
4 formulasHenderson–Hasselbalch in both its acid and base forms, plus the pKa and pKb conversions that feed them — buffer pH from a ratio.