Percent Ionized at a pH
Percent of a weak acid or weak base that is ionized at a pH, from its pKa.
Open the tool → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- The drug is a weak acid or a weak base
- Weak acid
- pKa
- 4
- pH
- 5
Result: 90.9% ionized and 9.1% un-ionized at pH 5.
The tool opens with these values already filled in. Replace them with your own.
What you enter
- The drug is a weak acid or a weak base
- pKa (for a weak base, of its conjugate acid)
- pH
How this is calculated
Citation
Physical chemistry: the mass-action expression for a weak acid, solved for the ionized fraction. Weak acid: 100 ÷ (1 + 10^(pKa − pH)); weak base: 100 ÷ (1 + 10^(pH − pKa)). The pKa is the reader's own figure.
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.