Acid–Base Titration: Overview

Acid-base titration can be performed to determine an unknown concentration of acid using a known concentration of a base or vice versa. 

When titrating an acid with a base, the titrant is gradually added to the acid, raising the pH. The pH change is plotted against the volume of the base to create a titration or pH curve.

The titration curves are S-shaped, though differences exist depending on whether the acid is strong or weak.

The pH at the start of the titration will be acidic but higher for a weak acid, assuming equal initial concentrations of acid.

The equivalence point is the point on the titration curve at which the moles of base equals the moles of acid in solution.

In the case of a strong acid, the equivalence point is reached when a strong base neutralizes all the hydronium ions produced by the strong acid; therefore, it always occurs at pH 7.

In contrast, a weak acid's equivalence point occurs at a pH greater than 7 and is reached when all the weak acid is converted into its conjugate base.

Near the equivalence point, there is a sudden jump in the pH of the solution. However, in a weak acid titration, this rapid pH shift is not as steep as in a strong acid titration.