Equivalence point is above pH 7 and the half-equivalence pH equals pKa.
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When a weak acid is titrated with a strong base, the initial pH is higher than that of a strong acid of the same concentration because the weak acid is only partly ionized. A buffer region forms before equivalence, where the solution contains both the weak acid and its conjugate base, and the pH changes slowly. At the half-equivalence point the concentrations of acid and conjugate base are equal, so pH equals pKa, which allows the pKa to be read directly. At the equivalence point the solution contains the conjugate base, which hydrolyses to give a pH above 7. The steep rise at equivalence is smaller than for a strong acid.
Key ideas: Four zones: initial weak-acid pH (ICE), buffer region using Henderson-Hasselbalch, equivalence where only A- remains (pH from Kb, above 7), and excess OH- beyond. At half-equivalence pH = pKa. For 0.100 M acetic acid titrated with NaOH, the equivalence pH is about 8.7.
Common mistakes and connections: Errors: applying Henderson-Hasselbalch at the equivalence point (no HA left), ignoring dilution at equivalence, and picking methyl orange as indicator (it changes too early). Use phenolphthalein, range 8.2 to 10. Starting pH rises more quickly than for strong acids because the buffer forms immediately.
Weak acid with strong base: a buffer region precedes equivalence, pH equals pKa at the half-equivalence point, and equivalence lies above pH 7. The interactive lesson shows this as a live animation or chart.
Titrating acetic acid with NaOH gives an equivalence point at about pH 8.7.
Equivalence point is above pH 7 and the half-equivalence pH equals pKa.
Weak Acid Strong Base Titration is a advanced topic in Acids, Bases & Electrochemistry. It builds on beginner and intermediate topics, so review those first if needed.
Study these earlier topics in Acids, Bases & Electrochemistry first: End Point, Titration Curve, Strong Acid Strong Base Titration.
The next topics in Acids, Bases & Electrochemistry are Acid-Base Indicators and Universal Indicator.
Yes. The interactive lesson includes a self-check question on Weak Acid Strong Base Titration, and the Acids, Bases & Electrochemistry quiz draws on every topic in this area.
Weak Acid Strong Base Titration is topic 27 of 105 in Acids, Bases & Electrochemistry.