Simulate acid-base titrations with real-time pH curve plotting. Identify equivalence points, buffers, and indicator color changes.
Choose the analyte - an acid or base with its concentration and volume - and the titrant, and the tool computes the pH of the mixture at every added volume, plotting pH against titrant volume. The curve shows the initial pH, the steep equivalence jump, the flat buffer plateau, and the color-change range of a chosen indicator on the same axes. The common surprise: the equivalence point is not pH 7 unless both reagents are strong. For a weak acid titrated by a strong base it lands near 9, and pH at half-equivalence equals the acid's pKa.
A concrete input and expected output from the current implementation.
Input
Titrate 25.0 mL of 0.100 M acetic acid (pKa 4.75) with 0.100 M NaOH
Expected output
pH 2.88 at 0 mL added; pH 4.75 at 12.5 mL (half-equivalence, buffer); pH 8.72 at 25.0 mL (equivalence point, steepest jump); pH 11.68 at 27.5 mL
The start is a 0.100 M weak acid, so pH = (pKa - log C)/2 = 2.88. At 12.5 mL, half the acid is converted to acetate and the buffer ratio is 1:1, so pH = pKa. At 25.0 mL the solution is 0.050 M sodium acetate, whose hydrolysis makes pH 8.72 rather than 7; the 2.5 mL excess of strong base afterwards dominates, driving pH to 11.68.
Each point on the curve is the equilibrium pH of the solution after that volume of titrant: strong reagents dissociate fully, weak ones set the pH through their Ka or Kb, and water's own ionization matters only at the extremes. The dominant species flips from acid to conjugate base as you pass the equivalence volume, which is what makes the jump steep.
The tool marks the equivalence point at the steepest slope, the half-equivalence buffer point where pH equals the weak acid's pKa, and the pH window where a chosen indicator changes color. Weaker acids and more dilute solutions give shallower jumps and flatter plateaus, so the same nominal titration looks different when Ka is one or two orders of magnitude smaller.
Because the salt left at equivalence is basic: the acid has been fully converted to its conjugate base, which pulls a proton from water and releases hydroxide. pH 7 at equivalence happens only when both reagents are strong, like HCl with NaOH. The tool is behaving correctly; the basic endpoint is the weak-acid case's real behavior.
Indirectly, yes. Simulate with your known titrant concentration and adjust the acid's concentration until the simulated equivalence volume matches what you measured; at equivalence the moles of base added equal the moles of acid, so C_acid = C_base x V_base / V_acid. The tool draws the curve; the back-calculation is stoichiometry you can verify by hand.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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