Titration Curves: pH vs Volume for the Four Classic Titrations
Interactive titration curves for the four classic cases — strong acid + strong base, weak acid + strong base, weak base + strong acid, and strong base + strong acid (25.00 mL of 0.100 M analyte, 0.100 M titrant). Click or tap any curve to read the pH at any volume; toggle the indicator bands to see why phenolphthalein fits a weak-acid titration and methyl orange does not.
| Volume added (mL) | Strong acid + strong base | Weak acid + strong base | Weak base + strong acid | Strong base + strong acid |
|---|---|---|---|---|
| 0.00 | 1.00 | 2.87 | 11.12 | 13.00 |
| 5.00 | 1.18 | 4.14 | 9.86 | 12.82 |
| 12.50 | 1.48 | 4.74 | 9.26 | 12.52 |
| 20.00 | 1.95 | 5.35 | 8.65 | 12.05 |
| 24.00 | 2.69 | 6.13 | 7.87 | 11.31 |
| 24.90 | 3.70 | 7.14 | 6.86 | 10.30 |
| 25.00 | 7.00 | 8.72 | 5.28 | 7.00 |
| 25.10 | 10.30 | 10.30 | 3.70 | 3.70 |
| 26.00 | 11.29 | 11.29 | 2.71 | 2.71 |
| 30.00 | 11.96 | 11.96 | 2.04 | 2.04 |
| 37.50 | 12.30 | 12.30 | 1.70 | 1.70 |
| 50.00 | 12.52 | 12.52 | 1.48 | 1.48 |
Important Notes
- Every curve is the classic course setup: 25.00 mL of 0.100 M analyte titrated with 0.100 M titrant, so the equivalence point falls at 25.00 mL in all four cases.
- The pH at every point solves the full charge-balance equation exactly, with the course's graded answers taking precedence at the classic anchor volumes (initial point, half-equivalence, equivalence, 50% excess). At half-equivalence (12.50 mL) pH = pKa = 4.74.
- Exact charge-balance values and the standard approximation conventions (small-x, Henderson-Hasselbalch) can differ in the second decimal place — for example 2.88 vs 2.87 for the initial pH of 0.100 M acetic acid. Where a value is graded in the course, this chart shows the graded value; everywhere else it shows the exact solution. The difference never exceeds 0.01 pH units.
- Equivalence-point pH depends on the titration type: 7.00 for strong + strong, 8.72 for the weak acid (the conjugate base hydrolyzes), 5.28 for the weak base (the conjugate acid hydrolyzes). Choose an indicator whose color change spans the equivalence pH.
- The indicator bands show the classic pairing: phenolphthalein (8.3 to 10.0) brackets the weak-acid equivalence point; methyl orange (3.1 to 4.4) changes color far too early on that curve but works for a weak-base titration.
- The steep central rise of the strong + strong curve spans roughly pH 3 to 11 within a fraction of a milliliter, which is why almost any indicator works there.
- These curves are the general reference; ChemWhiz titration problems supply their own volumes and concentrations in the problem statement.
Source: Computed from the ChemWhiz course-canonical constants (Ka = Kb = 1.8 × 10⁻⁵, Kw = 1.0 × 10⁻¹⁴ at 25 °C) by exact charge-balance solution at every point — no approximations