titration curve

Meaning: A titration curve plots the pH of the analyte against the volume of titrant added. The pH changes slowly, rises steeply through the equivalence point, then levels off. Strong acid with strong base: equivalence at pH 7 (25 °C). Weak acid with strong base: above 7, since the conjugate base hydrolyzes water. Weak base with strong acid: below 7. A weak acid also has a flat buffer region centered on the half-equivalence point, where [HA] = [A⁻] and pH = pKa. A polyprotic acid shows one steep rise per proton.

Equation: pH = pKa + log([A⁻]/[HA]); concentrations in mol/L, pH and pKa unitless. At equivalence (monoprotic, 1:1): MaVa = MbVb, with M in mol/L and V in L.

On the MCAT: Given a curve, you locate the equivalence point, read pKa from the half-equivalence volume, tell weak from strong by the starting pH, choose an indicator whose color-change range falls on the steep section, or find an unknown concentration.

Common confusion: The equivalence point is not always pH 7; the salt formed sets its pH. It is also not the endpoint, which is where the indicator changes color. Read pKa at half the equivalence volume, not at the steep rise.