Titration Curve Calculator
Simulate a titration of a monoprotic acid with a strong base and inspect the pH curve.
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What it does
The titration curve calculator simulates the titration of a monoprotic acid with a strong monoprotic base and plots the pH as a function of added base. It is used by students and analysts to understand acid-base behavior and to locate the equivalence point of a titration.
How it works
The tool models one acid titrated by one strong base. For a strong acid such as HCl, the initial pH is -log10([H+]) = -log10(Ca), and near the equivalence point the pH rises steeply through 7. For a weak acid, the initial pH is set by its Ka, and in the buffer region the pH follows the Henderson-Hasselbalch equation pH = pKa + log10([A-]/[HA]). At the equivalence point the weak acid has been converted to its conjugate base, so the pH there is above 7 and is found from the hydrolysis of A-. The equivalence volume is the base volume that neutralizes all acid: V_eq = Ca × Va / Cb, where Ca and Va are acid concentration and volume and Cb is base concentration.
Worked example
Titrate 25.0 mL of 0.100 M acetic acid (pKa 4.76) with 0.100 M NaOH. The initial pH from Ka is about 2.88. The equivalence volume is V_eq = (0.100 M × 25.0 mL) / 0.100 M = 25.0 mL. At the half-equivalence point (12.5 mL added) pH = pKa = 4.76. At equivalence the solution is sodium acetate, whose hydrolysis gives a pH of about 8.72. The curve rises steeply around 25 mL.
When to use it
Use it to preview the shape of a titration before running it in the lab and to choose an indicator. Use it to find the equivalence volume and equivalence pH for a weak-acid standardization. Use it in teaching to show how the buffer region and the pKa appear on the curve.
FAQ
- What does a titration curve show?
- It plots the pH of the acid solution as strong base is added. You see a slow buffer region, a steep rise near the equivalence point, and the equivalence volume where all acid is neutralized.
- How do I calculate the equivalence volume?
- Use stoichiometry: V_eq = Ca × Va / Cb, where Ca and Va are the acid concentration and volume and Cb is the base concentration. At equivalence, moles of base equal moles of acid.
- Why is the equivalence point above 7 for a weak acid titrated with a strong base?
- At equivalence the weak acid has become its conjugate base, which hydrolyzes water to produce OH-, so the pH is above 7. For a strong acid titrated with a strong base the equivalence pH is 7.
- What pH do I read at the half-equivalence point?
- For a weak acid, at half equivalence the amounts of acid and conjugate base are equal, so by Henderson-Hasselbalch the pH equals the pKa.