Titration Calculator

Introduction

Acid–base titration uses a measured titrant to find an unknown acid or base concentration at the equivalence point, where stoichiometric acid equivalents equal base equivalents. This calculator applies Ca·Va·na = Cb·Vb·nb, the same relation behind molarity and solution concentration work. It follows the IUPAC idea of amount concentration and equivalence used in volumetric analysis (see the IUPAC Gold Book and LibreTexts titration overview).

What this titration calculator solves

Enter any three of Ca, Va, Cb, and Vb plus the stoichiometric equivalence numbers na and nb. The calculator solves the missing term for acid concentration, acid volume, base concentration, or base volume. Volumes may be in millilitres or litres as long as Va and Vb use the same unit.

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  Default: solve Ca, the unknown acid/analyte concentration.

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  Use solve Cb when a standardized acid determines a base concentration.

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  Use solve Vb to plan the titrant volume needed before a lab run.

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  Use solve Va to back-calculate the aliquot neutralized by a known titrant.

Equivalence-point formula

At equivalence, acid equivalents equal base equivalents: Ca × Va × na = Cb × Vb × nb. The concentration terms are mol/L, the volume terms are matching volume units, and n values count reactive H+ or OH− equivalents per formula unit. For monoprotic HCl and NaOH, na = nb = 1, so the relation simplifies to CaVa = CbVb.

Choosing na and nb

The n values are not coefficients from a balanced equation by themselves; they represent the number of acidic or basic equivalents per mole that react in the titration. HCl, HNO3, KOH, and NaOH usually have n = 1. Sulfuric acid commonly uses na = 2 for complete neutralization, while Ca(OH)2 uses nb = 2.

Endpoint vs equivalence point

The equivalence point is the theoretical stoichiometric point where acid and base equivalents are exactly balanced. The endpoint is the observed signal, often a colour change from an indicator. Good titrations choose an indicator whose transition range falls on the steep part of the titration curve, so the endpoint is as close as possible to the equivalence point.

Indicator and pH guidance

Indicator choice depends on the pH near equivalence, not just on whether the analyte is an acid or a base. Strong acid–strong base titrations have a sharp jump near pH 7, many weak acid–strong base titrations have basic equivalence points, and weak base–strong acid titrations have acidic equivalence points. Estimate solution pH with the pH calculator or buffer regions with the buffer pH calculator.

Strong acid + strong base:

bromothymol blue or phenolphthalein often works.

Weak acid + strong base:

phenolphthalein is usually suitable.

Strong acid + weak base:

methyl orange or methyl red may be suitable.

Weak acid + weak base:

a pH meter is usually preferred over a visual indicator.

Practical accuracy tips

Titration precision depends on standardization, clean glassware, careful meniscus reading, and avoiding overshooting the endpoint. Rinse the burette with titrant, remove air bubbles from the tip, swirl continuously, and approach the endpoint dropwise. For detailed lab practice, compare with university analytical chemistry notes such as UC Davis LibreTexts and standards organizations such as NIST.