Measure acidity from concentration, Ka, hydronium, or hydroxide. Compare strong and weak acid behavior instantly. Visualize pH trends clearly with exports, formulas, and examples.
1. Direct hydronium: pH = -log10([H3O+])
2. Direct hydroxide: pOH = -log10([OH-]) and pH = pKw - pOH
3. Strong acid model: [H3O+] = C × n, where C is acid molarity and n is acidic protons released per mole.
4. Weak acid equilibrium: Ka = x² / (C - x), solved exactly as x = (-Ka + √(Ka² + 4KaC)) / 2
5. Water relationship: pKw = -log10(Kw), and pH + pOH = pKw
6. Percent dissociation: % dissociation = ([H3O+] / C) × 100
1. Choose the method that matches your available chemistry data.
2. Keep Kw at 1.0 × 10^-14 for standard 25°C work, or update it for another temperature.
3. Enter concentration values in molarity.
4. For strong acids, provide concentration and acidic proton count.
5. For weak acids, provide initial concentration and either Ka or pKa.
6. Click Calculate Acidity to show the result summary above the form.
7. Review the graph, export the summary to CSV, or save it as PDF.
| Scenario | Input Values | Estimated pH | Interpretation |
|---|---|---|---|
| Strong monoprotic acid | 0.010 M HCl, n = 1 | 2.0000 | Clearly acidic due to full dissociation. |
| Strong diprotic assumption | 0.005 M acid, n = 2 | 2.0000 | Effective hydronium equals 0.010 M. |
| Weak acid equilibrium | 0.10 M acid, Ka = 1.8 × 10^-5 | 2.8753 | Only a small fraction dissociates. |
| Direct hydronium input | [H3O+] = 3.2 × 10^-4 M | 3.4949 | Slightly less acidic than 0.001 M hydronium. |
It calculates pH, pOH, hydronium concentration, hydroxide concentration, and related acidity indicators from strong acid, weak acid, hydronium, or hydroxide inputs.
Yes. In weak acid mode, you can enter pKa if Ka is unavailable. The calculator converts pKa to Ka automatically before solving the equilibrium expression.
Kw changes with temperature. Editing it lets you adapt the pH and pOH relationship for conditions other than the standard 25°C chemistry assumption.
Yes. That mode assumes the acid releases all listed acidic protons completely. It is most suitable for textbook strong-acid calculations and dilute ideal solutions.
The calculator uses the exact quadratic solution of the acid equilibrium expression rather than a rough approximation, which improves accuracy for broader concentration ranges.
Yes. Very concentrated acid solutions can produce negative pH values mathematically. That result indicates extremely high hydronium concentration, not an error.
Because this page lets you change Kw. When Kw differs from 1.0 × 10^-14, pKw changes, so pH + pOH equals pKw instead of 14.
Export the summary when you want a clean record of method, pH, pOH, ion concentrations, classification, and model details for reports or lab notes.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.