My Easy Science
Titration Curve Simulator
Add base drop by drop and watch the pH jump. Find the equivalence point and pick an indicator that changes colour there.
Set the titration and the indicator, then tap Draw the curve.
For learning only. Not for patient care decisions. Always check with a qualified professional and the product label.
Indicator
| Value | Result |
|---|---|
| Colour change starts | — |
| Colour change ends | — |
| Suitable? | — |
An indicator is suitable when its colour change happens within about 1 mL of the equivalence point.
pH data
| Titrant added | Volume (mL) | pH |
|---|---|---|
| 0% (start) | — | — |
| 25% | — | — |
| 50% (half-equivalence) | — | — |
| 75% | — | — |
| 90% | — | — |
| 99% | — | — |
| 100% (equivalence) | — | — |
| 101% | — | — |
| 110% | — | — |
pH at each stage of the titration.
Starting values
Worked example: 25.00 mL of 0.100 M HCl with 0.100 M NaOH — pH 1.00 at 0 mL, 3.70 at 24.9 mL, 7.00 at 25.0 mL, 10.30 at 25.1 mL.
How it works
Checked against hand-worked examples (see the page source comments).
Results are shown to 2 decimal places.
A titration adds a base to an acid, or an acid to a base, one drop at a time. The pH barely moves at first, then jumps almost vertically at the equivalence point, where the moles of acid and base are exactly equal. That jump is what you watch for. The equivalence volume is just the analyte moles divided by the titrant concentration: 25 mL of 0.1 M acid needs 25 mL of 0.1 M base.
For a strong acid and a strong base the jump passes through pH 7, so the equivalence pH is 7. For a weak acid the story is different: before the equivalence point the mixture is a buffer, so pH = pKa + log([A−]/[HA]), and at half-equivalence the pH equals the pKa. At the equivalence point only the conjugate base is left, and it pulls a proton from water, so the pH is above 7. For acetic acid, pKa 4.76, the equivalence pH is 8.73.
An indicator is a dye that changes colour over a small pH range. It is only useful if that change happens right at the equivalence point. Phenolphthalein, 8.2 to 10.0, is right for a weak acid titration, because the equivalence pH is 8.73. Methyl orange, 3.1 to 4.4, changes colour long before the equivalence point in that titration, in the buffer region, so it would give a wrong answer. For a strong acid and strong base the jump is so steep that almost any indicator works, because the pH flies through every range within a drop or two of equivalence.