Strong Acid pH Calculator

How it is calculated

The acid is assumed to be strong and monoprotic, so it releases exactly one hydrogen ion per molecule and dissociates completely: [H⁺] = c, where c is the concentration in mol/L. Then pH = −log₁₀(c) and pOH = 14 − pH, with both shown to two decimals. The value 14 holds for water at 25 °C; at other temperatures it changes. The concentration must be above zero. The tool does not include the hydrogen ions coming from water itself, so it is not meaningful for very dilute solutions (around 10⁻⁷ mol/L or lower), and it does not handle weak acids or acids that release more than one proton.

Common mistakes

• Applying the tool to sulfuric acid or another diprotic acid with the molarity unchanged. Each mole releases more than one H⁺, so the concentration you enter should be the hydrogen-ion concentration, not the acid's.
• Using it for acetic acid, citric acid or other weak acids. They dissociate only partly, so the real pH is noticeably higher than the number shown.
• Typing the concentration in mmol/L or as a percentage. The field is in mol/L, so 25 mmol/L must be entered as 0.025.
• Trusting very dilute inputs. At 10⁻¹⁰ mol/L the tool returns a pH of 10, which would describe a base; water's own ions dominate there, and the formula no longer applies.
• Assuming a negative pH is an error. Concentrated strong acids above 1 mol/L give a pH below 0, for example about −0.70 at 5 mol/L, which is the formula's output, although real solutions deviate at such concentrations.