pH from Concentration Calculator
Calculate the pH of a strong acid or base solution from its molar concentration.
How it works
pH = −log₁₀[H⁺] · pOH = −log₁₀[OH⁻] · pH + pOH = 14 (25 °C)
pH measures how acidic or basic a solution is on a logarithmic scale: the negative base-10 logarithm of the hydrogen-ion concentration. For a strong acid, which dissociates completely, the H⁺ concentration equals the acid concentration. For a strong base you find pOH from the OH⁻ concentration first, then subtract from 14 to reach pH. Each whole pH unit is a tenfold change in acidity.
Worked example
A 0.01 mol/L solution of a strong acid has [H⁺] = 0.01 = 10⁻², so pH = −log₁₀(10⁻²) = 2 — clearly acidic.
Sources: pH — Wikipedia
Frequently asked questions
Why does pH 7 mean neutral?
At 25 °C pure water self-ionises so that [H⁺] = [OH⁻] = 10⁻⁷ mol/L, giving pH 7. Below 7 the H⁺ concentration is higher (acidic); above 7 it is lower (basic).
Does this work for weak acids?
No. Weak acids only partly dissociate, so [H⁺] is less than the acid concentration and depends on the acid dissociation constant Ka. This calculator assumes complete dissociation, which is valid for strong acids and bases.
What does a negative pH mean?
Very concentrated strong acids (above 1 mol/L H⁺) can give a pH below 0. It is unusual but real — the formula simply returns the negative logarithm.
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