Equivalence and endpoint are not identical
The equivalence point is the stoichiometric target, while the endpoint is the color or instrument signal you observe experimentally.
Titration Calculator
Inputs
Needed only for weak-acid or weak-base modes.
Results
Current point
pH -
Region: -
Neutralized: -
Key volumes
Equivalence volume: -
Half-equivalence volume: -
Volume remaining to equivalence: -
Stoichiometry
Initial analyte moles: -
Titrant moles added: -
Excess species: -
Checkpoint notes
-
Characteristic points
| Point | Added titrant | pH | What dominates |
|---|---|---|---|
| Enter values and calculate to populate the titration checkpoints. | |||
Half-equivalence is reported only for weak-acid and weak-base cases. Values assume idealized aqueous behavior at 25 C.
Worked example
Weak acid with strong base: 25.0 mL of 0.100 M acetic acid titrated by 0.100 M NaOH, with pKa = 4.76.
- Initial moles of acid = 0.100 x 0.0250 = 0.00250 mol.
- Equivalence volume = 0.00250 / 0.100 = 0.0250 L = 25.0 mL.
- At 12.5 mL added, the system is at half-equivalence, so pH is approximately pKa = 4.76.
- At 25.0 mL added, acetate remains and the equivalence-point pH is above 7 because the conjugate base hydrolyzes water.
How this titration calculator works
This tool treats the analyte as a monoprotic acid or base and applies the standard piecewise acid-base titration logic. First it finds the initial analyte moles, then it compares them with the moles of titrant added. From that stoichiometric check, the page decides whether you are before equivalence, exactly at equivalence, or past equivalence.
For strong acid-strong base and strong base-strong acid setups, the pH comes from the excess strong species after neutralization. For weak-acid and weak-base titrations, the calculator uses the weak equilibrium where appropriate: the initial weak solution is solved from its dissociation constant, the buffer region uses the Henderson-Hasselbalch relationship, and the equivalence point uses conjugate-species hydrolysis.
n = C x VVeq = nanalyte / CtitrantpH = pKa + log10(base/acid)pOH = pKb + log10(conjugate acid/base)
Assumptions: water at 25 C, monoprotic acid-base chemistry, no activity-coefficient correction, and no polyprotic, precipitation, complexometric, or redox behavior. This is appropriate for classroom work and quick bench estimates, not regulated analytical reporting.
Reading the output
- Current point tells you the pH at the exact titrant volume entered.
- Key volumes shows the equivalence volume, plus half-equivalence when a weak analyte is involved.
- Stoichiometry reports initial analyte moles, titrant moles added, and which species is in excess.
- Characteristic points summarizes the initial solution, half-equivalence if relevant, the equivalence point, and your current point.
5 titration facts
Half-equivalence is special for weak systems
For a weak acid titrated by strong base, the pH at half-equivalence is approximately pKa. For weak bases, the matching pOH is approximately pKb.
Only strong acid and strong base land near pH 7 at equivalence
Weak analytes leave conjugate species behind, so hydrolysis shifts the equivalence-point pH above or below neutral.
Titration curves are steepest near equivalence
That rapid pH change is why indicators are chosen to change color in the region where the curve rises most sharply.
Accurate volume reading matters twice
Buret reading error affects both the calculated moles of titrant and your interpretation of where you are on the titration curve.
FAQ
When is pH = 7 at equivalence?
Only in the strong acid-strong base case, under the usual 25 C textbook assumption. Weak-acid and weak-base titrations shift the equivalence point because the conjugate species hydrolyzes water.
Can I use Ka or Kb directly?
Yes. Switch the weak-system constant selector to Use Ka / Kb. For weak acids enter Ka, and for weak bases enter Kb.
Why does the half-equivalence pH equal pKa for weak acids?
At half-equivalence the weak acid and its conjugate base are present in equal moles, so the logarithmic ratio term becomes zero. The same logic gives pOH = pKb for weak bases.
Does this support diprotic or triprotic systems?
No. The calculator is intentionally limited to one-step monoprotic titrations so the assumptions stay clear and the results remain interpretable.
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Limits and lab note
Use this as a study aid or planning helper, not as a substitute for a validated analytical method. Real titrations can deviate because of activity effects, temperature shifts, dissolved carbon dioxide, indicator choice, ionic strength, or non-monoprotic chemistry.