Weak Acid-Strong Base Titration
The graph below is a titration curve for a weak acid and a strong base. A typical net ionic equation for the reaction is:
HC2H3O2(aq) + OH –(aq) —> C2H3O2–(aq) + H2O(l)
if using an acid such as acetic acid and a strong base such as sodium hydroxide.
The titration curve for a weak acid, unlike a strong acid, begins at a higher pH and maintains a higher pH up to the equivalence point. Because a weak acid does not ionize completely it supplies fewer hydrogen ions which results in a higher pH.
Unlike with a strong acid, the pH rises more rapidly during the early stages of the titration. It then quickly levels off half-way through the titration. The weak acid, HC2H3O2, and its conjugate base, C2H3O2–, produce a buffering effect which resists changes in pH as small amounts of base are added.
Unlike with a strong acid, there are smaller changes in pH near the equivalence point. The weaker the titrated acid the less the pH change will be at the equivalence point. Neutralization produces water, Na+, and C2H3O2–. The C2H3O2– is a weak base which makes the pH of the solution always greater than 7.00.
After the equivalence point has been reached, the titration curve for the weak acid is the same as the titration curve for the strong acid because the pH depends on the excess OH – in both titrations.
