pH from a concentration, and back
Any one of pH, pOH, [H⁺], [OH⁻] unlocks the other three — the 25 °C relations in one step.
Tools used in this guide
The job
Lab work and pool chemistry both ask the same questions in different units. pH = −log₁₀[H⁺] and pH + pOH = 14 at 25 °C are the whole mechanism.
One field in, three out
Enter whichever value you have — a pH of 3.5, or 2e-4 mol/L of H⁺ — and the other three appear. Concentrations take scientific notation.
Worked example
[H⁺] = 1e-4 → pH 4.0, pOH 10.0, [OH⁻] = 1e-10. A neutral 7.0 balances at [H⁺] = [OH⁻] = 1e-7.
Where it stops
Ideal dilute solutions at 25 °C: no activity coefficients, so concentrated acid reads optimistically. Weak acids need Ka and the quadratic — this is the strong/ideal case only.