pH and Ion Concentration Calculator
Convert pH and ion concentrations or model a single strong or weak monoprotic acid/base. Include water autoionization instead of ignoring dilute-solution effects.
YOUR CALCULATION
Result
—
Calculation steps
Work through one step at a time or reveal the complete calculation. The steps use your current inputs.
How to calculate
Use pH=−log10[H₃O⁺] and [H₃O⁺][OH⁻]=Kw in the ideal concentration model. For an acid/base input, enforce charge balance including water. For a weak species also enforce its mass balance and dissociation equilibrium.
Strong acid H=(C+√(C²+4Kw))/2; weak acid H−Kw/H=C Ka/(Ka+H)
Worked example
A 0.001 mol/L strong monoprotic acid with Kw=1e−14 gives pH very close to 3. Pure water has pH 7 only when Kw=1e−14. A very dilute strong acid approaches the neutral pH from below.
Assumptions and input details
Aqueous ideal concentration approximation: thermodynamic pH uses activity. Kw defaults to 1e−14 near 25°C; edit Kw for a different scenario, because temperature is not automatically modeled. The acid/base models describe one neutral monoprotic acid or monobasic base with its counterion, complete strong-species dissociation and no added salts/buffer. Concentration is 0–10 mol/L; Ka/Kb 1e−20–1e4. Direct pH is −3–30; direct ion concentration positive. Resulting ion concentrations must be 1e−30–1000 mol/L. High concentrations can be strongly nonideal. Polyprotic species, mixtures and ionic-strength corrections are unsupported.
References: OpenStax pH and pOH · OpenStax acid/base equilibria
Using this calculator
Can I enter my own problem?
Yes. Replace the example values with your own inputs. The result, calculation steps, tables and applicable diagrams update from those inputs. Blank or invalid values clear the result; example values are never silently substituted for missing inputs.
Are the results exact?
Results use floating-point arithmetic and displayed rounding. Read the formula, assumptions and any stated data precision before interpreting the result.
Is my input uploaded?
The calculation runs in your browser. No account, file upload or external AI service is required. Inputs are not saved between page reloads.
Convert mass fraction, mass percent, mass ppm, g/L, mg/L and mol/L using an explicit solution density and solute molar mass.
Enter a chemical formula and mass or amount of substance. Find molar mass, moles and particle count with an element-by-element breakdown.
Calculate the stock quantity needed for a target concentration and final batch size. Choose a concentration basis and see dilution factors, steps and batch-size comparisons.
Reserved advertising space.