What does pKb tell you?

pKb measures base strength on a logarithmic scale. Lower pKb means stronger base. Each unit decrease represents a 10-fold increase in base strength.

How are pKa and pKb related?

For a conjugate acid-base pair at 25°C, pKa + pKb = 14. This comes from Ka × Kb = Kw = 10⁻¹⁴.

How do I convert pKb back to Kb?

Kb = 10^(-pKb). For example, pKb = 4.74 gives Kb = 10^(-4.74) = 1.82 × 10⁻⁵.

Free pKb Calculator

Calculate pKb from the base dissociation constant Kb, or convert between Kb and pKb values.

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Kb (Base Dissociation Constant)

pKb

4.74

View formula & how it works →

How to Calculate pKb

Formula

pKb = −log₁₀(Kb)

Where:

pKb = negative base-10 logarithm of Kb

Kb = base dissociation constant

A lower pKb indicates a stronger base. pKa + pKb = 14 at 25°C for a conjugate pair.

Example Calculation

Ammonia has Kb = 1.8 × 10⁻⁵.

01pKb = -log₁₀(Kb)
02pKb = -log₁₀(1.8 × 10⁻⁵)
03pKb = 4.74

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