Ka to pKa Converter (and Kb, pKb)
Enter Ka, pKa, Kb or pKb to see all four values.
Your numbers
For Ka and Kb enter a number like 1.75e-5
Your results
Ka
Ka
—
pKa
—
Kb of the conjugate base
—
pKb
—
Acid strength
—
Ka to pKa Converter (and Kb, pKb) by TheCalcTools
How the Ka to pKa Converter (and Kb, pKb) works
pKa = −log₁₀ Ka. A smaller pKa means a stronger acid. For a conjugate acid-base pair in water at 25 °C, Ka × Kb = Kw = 1.0 × 10⁻¹⁴, so pKa + pKb = 14.
The formula
pKa = −log₁₀ Ka; pKa + pKb = 14 (25 °C)
Worked example
Using the default values shown in the calculator:
| I know | Ka |
|---|---|
| Value | 1.75e-05 |
- Ka 1.75 × 10⁻⁵ → pKa 4.757; the conjugate base has pKb 9.243.
Result:
| Ka | 0.0000175 |
|---|---|
| pKa | 4.757 |
| Kb of the conjugate base | 5.714e-10 |
| pKb | 9.243 |
| Acid strength | Weak acid |
Frequently asked questions
Why 14?
pKw is 14.00 at 25 °C. It changes with temperature (about 13.6 at 37 °C).
Sources and further reading
Related calculators
More in Chemistry · All calculators
This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.