Plot acid-base titration curves in real time.
The titration curve is one of the most powerful analytical tools in chemistry, forming the backbone of AP Chemistry Unit 8 and appearing consistently on USNCO and IChO examinations. Mastering titration goes beyond knowing that moles of acid equal moles of base at the equivalence point — it requires understanding the pH behavior at every stage of the reaction.
In a strong acid–strong base titration, such as HCl with NaOH, the equivalence point occurs exactly at pH 7.00, because the resulting salt (NaCl) does not undergo hydrolysis. The steep, near-vertical jump in pH around the equivalence point makes indicator selection flexible: phenolphthalein, methyl orange, or even bromothymol blue all work reliably.
Weak acid titrations reveal a richer landscape. When acetic acid (Ka = 1.8 × 10⁻⁵) is titrated with NaOH, the half-equivalence point falls at pH = pKa = 4.74. This point marks the center of the buffer region, where the concentration of the acid equals the concentration of its conjugate base and pH changes most gradually with added titrant. The Henderson–Hasselbalch equation (pH = pKa + log [A⁻]/[HA]) governs the buffer region precisely.
The equivalence point for a weak acid–strong base titration falls above pH 7, because the conjugate base formed (e.g., CH₃COO⁻) hydrolyzes water to release OH⁻. This is a common AP exam misconception — students who memorize "equivalence = pH 7" miss the fact that only strong acid–strong base systems meet exactly at neutral pH.
Polyprotic acids like H₂SO₄, H₃PO₄, and H₂CO₃ produce multiple equivalence points — one per ionizable proton — each separated by a distinct buffer region governed by its own Ka. Recognizing multiple inflection points on a titration curve is a common question type in both the AP MCQ and USNCO local exam.
This free titration simulator lets you explore all these scenarios in real time. Adjust acid and base concentrations, select strong or weak systems, enable polyprotic acids, and watch the full S-curve plot update instantly. The equivalence point, half-equivalence point, buffer region, and indicator transition zones are marked automatically, making it an ideal study tool for exam preparation.