Acid-Base Titration Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/8/2026
At a titration's equivalence point, C(known) × V(known) = C(unknown) × V(unknown). For a titrant solution at 0.1 mol/L, of which 25 mL was added to titrate 20 mL of unknown solution, the unknown concentration is 0.125 mol/L.
Explanation
Acid-base titration is an experimental analytical chemistry method used to determine the unknown concentration of an acidic or basic solution, by reacting it with a solution of known concentration (the titrant), added gradually until the equivalence point — the precise moment when the amounts of acid and base added exactly neutralize each other. This point is generally identified by a color change of an indicator, or by a sharp jump in pH measured with a pH meter. At the equivalence point, the fundamental relationship C(known) × V(known) = C(unknown) × V(unknown) follows directly from the fact that the number of moles of H⁺ ions provided by the acid exactly equals the number of moles of OH⁻ ions provided by the base (for a simple acid-base reaction, with a single equivalent on each side): rearranging this equality directly isolates the unknown concentration sought. This technique remains a reference laboratory method for precisely determining a solution's concentration, widely used in quality control and chemical analysis. For acids or bases with multiple equivalents (such as sulfuric acid H₂SO₄, which releases two H⁺ per molecule), an additional multiplying factor must be included, which our solution normality calculator covers more generally. To determine a molar concentration directly from a dissolved mass rather than by experimental titration, see our molar concentration calculator.
Example: titrant at 0.1 mol/L, 25 mL added to titrate 20 mL
Inputs
Titrant concentration: 0.1 mol/L. Volume added at equivalence: 25 mL. Volume of the solution to titrate: 20 mL.
Calculation
Unknown concentration = (0.1 × 25) ÷ 20 = 2.5 ÷ 20 = 0.125 mol/L.
Result
The unknown solution's concentration is 0.125 mol/L.
Frequently asked questions
How is the equivalence point precisely identified in a real titration?
In practice, either a color indicator is used (a substance that changes color at a precise pH, chosen to match the expected pH at the equivalence point), or the pH is measured continuously with a pH meter while the titrant is added, with the equivalence point corresponding to the sharpest inflection point of the titration curve (the steepest pH jump).
Does this formula apply to any acid or base?
It applies directly to an acid-base reaction with a single equivalent on each side (a monoprotic acid like HCl with a monohydroxylic base like NaOH, for example). For species with multiple equivalents (such as H₂SO₄ or Ca(OH)₂), the number of equivalents of each species must be factored into the calculation, which our solution normality calculator does for a more general reading.
Why is the titrant added drop by drop near the equivalence point?
Because pH changes very rapidly as the equivalence point approaches (it is precisely this sharp jump that allows it to be identified): adding too quickly risks overshooting this exact point and skewing the measured volume, and therefore the final calculation of the unknown concentration. Slowing the addition near this point allows a more precise reading of the exact volume at the equivalence point.