How to use this calculator
- Select the known ion, acid, or base model.
- Enter the concentration.
- Enter the ion factor or dissociation constant when the mode requires it.
- Calculate pOH, pH, and both ion concentrations.
Formula and variables
pH = -log10[H+]; pOH = -log10[OH-]
| Symbol | Meaning | Unit |
|---|---|---|
| [H+] | hydrogen-ion activity approximation | mol/L |
| Kw | water ion product | (mol/L)² |
Worked example
A hydrogen-ion concentration of 0.010 mol/L gives pH 2.000 at the stated Kw reference.
Interpretation
pH and pOH are logarithmic. The complementary value depends on the disclosed temperature-specific water ion product.
Common mistakes
- Concentrations must be positive before taking a logarithm.
- Do not assume pH + pOH is always 14 without specifying temperature and Kw.
Frequently asked questions
How do I convert pOH to pH?
Use pH = pKw - pOH. At 25 degrees Celsius, pKw is approximately 14.
Can the calculator handle a weak base?
Yes. Select Weak base and enter its initial concentration and Kb.
Why does the tool show both ion concentrations?
The values provide a direct check of the selected Kw relationship.
Can I use scientific notation?
Yes. Enter values such as 6.022e23 or 1.0e-6 in a numeric field.
How should I round the result?
Keep extra digits during the calculation. Round the final result to the precision required by your data.