Choose a pH calculation model
The pH calculator provides separate models for a strong monoprotic acid, a strong monobasic base, and a weak monoprotic acid. Select the chemical situation before entering concentration. Separating these paths prevents a strong-acid shortcut from being silently applied to a weak acid or a hydroxide calculation from being mistaken for hydrogen-ion concentration.
Strong modes assume complete one-for-one dissociation. Weak-acid mode uses formal acid concentration and Ka, then solves the simple equilibrium quadratic. Every path displays hydrogen or hydroxide concentration, logarithm steps, and the assumptions behind the reported pH estimate.
Calculate strong acid or strong base pH
For the strong-acid model, [H+] is approximated by the entered acid concentration and pH is −log10[H+]. A 0.01 mol/L monoprotic strong acid therefore gives pH about 2. This does not apply unchanged to an acid that releases multiple protons or dissociates incompletely.
For the strong-base model, [OH−] is approximated by concentration, pOH is −log10[OH−], and pH = 14−pOH under the stated 25°C dilute-water assumption. A 0.01 mol/L one-for-one strong base gives pOH 2 and pH about 12.
Solve a weak monoprotic acid equilibrium
Weak-acid mode solves Ka = x²/(C−x), where x is the equilibrium hydrogen-ion concentration for the simplified HA equilibrium. The stable positive quadratic root is used instead of assuming x is negligible. The page also shows the common √(KaC) shortcut for comparison.
Percent ionization provides a practical approximation check. When ionization exceeds the familiar 5% guide, the square-root shortcut is flagged rather than presented as equally reliable. The exact simple root still belongs to a limited concentration model and does not include water autoionization, activity, or additional acid-base reactions.
Understand concentration pH versus activity pH
Thermodynamic pH is defined through hydrogen-ion activity. Classroom calculations often substitute concentration under dilute conditions, but ionic strength and activity coefficients can shift measured pH. Temperature also changes water autoionization, so pKw = 14 is not a universal constant at every temperature.
Very dilute strong-acid or strong-base inputs require a full water-equilibrium treatment, while concentrated solutions require activity models and may fall outside the ordinary aqueous pH scale interpretation. A numeric answer from a selected simple model is not proof that the real sample satisfies that model.
Measurement, safety, and private calculation
Use the result to understand formulas or check homework, then compare with calibrated measurement or a validated equilibrium method when pH affects health, environment, manufacturing, or chemical handling. The page does not identify a substance, assess corrosivity, recommend neutralization, or provide mixing instructions.
The values are calculated in the current browser tab. NexaCurrent does not upload the quantities, formulas, chemical names, element choices, or other information entered here, and no account is needed. Copying is a deliberate action after the answer and working are visible. Refreshing or leaving the page clears the current calculation, so keep a copied result if it is needed for later study.