pH, pOH & buffers

Conversion

Select the known quantity, enter its value and convert. Concentrations are in mol/L; decimal commas and scientific notation are accepted. Only the other quantities are listed. Changing the source reuses the calculated value if available. Reset restores pH 7 and clears the result.

Model

At 25 °C: pH = −log₁₀[H₃O⁺], pOH = −log₁₀[OH⁻], pH + pOH = 14. Neutral means pH 7; lower values are acidic and higher values basic. Values outside 0–14 are allowed. This is the ideal concentration convention; activities matter in concentrated solutions. Zero concentrations, overflow and inaccurate underflow are rejected.

Buffer estimate

For a conjugate weak acid HA and base A⁻: pH = pKₐ + log₁₀([A⁻]/[HA]). Choose pKₐ for the same temperature. Equilibrium concentrations give the ideal relation; using initial mixture concentrations is an approximation. The usual ratio 0.1–10 is a guideline, not a guarantee of buffer capacity. A warning also appears if predicted free hydronium exceeds 5% of HA or hydroxide exceeds 5% of A⁻. This screening does not replace solving coupled equilibria, water ionization or activities. It does not calculate added acid/base or buffer capacity.

Reload preserves inputs but requires calculation; switching tools retains unchanged results. Each tab resets independently.

References: OpenStax: pH and pOH; buffers.