Roughly sketch the titration curve \((\mathrm{pH}\) versus volume) that you would expect if you titrated a weak base with a strong acid. Mark the equivalence point.

The equivalence point in a titration is a critical moment where the amount of acid added exactly neutralizes the amount of the base present. For a weak base titrated with a strong acid, this equivalence point occurs at a pH below 7, unlike the titration of a strong base with a strong acid which would be at pH 7.

Visualized on a graph, the equivalence point is represented by a sharp change in pH. This is because, at this juncture, all the weak base has reacted with the strong acid to form water and a salt. The resulting solution is no longer buffered by the presence of the weak base or its conjugate acid, thus leading to a rapid shift in pH with each incremental addition of acid.

The buffering region of a titration curve reflects an area where the pH of the solution does not change significantly with the addition of the titrant. This occurs because the weak base present is being converted into its conjugate acid by the strong acid. During this time, the solution resists changes in pH due to this mixture of the base and its conjugate acid.

In weak base-strong acid titrations, the buffering region is seen as a flat section on the curve. Here, the pH gently decreases as the strong acid neutralizes the base. Notably, the midpoint of the buffer region is known as the half-equivalence point, where concentrations of the weak base and its conjugate acid are equal, setting the stage for a pH that reflects the pKa of the weak base.

pH titration analysis is a powerful tool for understanding the acid-base properties of a substance. The titration curve generated from this analysis provides a graphical representation of the change in pH as a titrant is added to the analyte solution. Points of interest on the curve include where the initial pH starts, indicative of base strength, the buffering and equivalence points, as well as the pH after excess titrant is added.

For instance, by analyzing a titration curve for a weak base with a strong acid, one can discern the pKa value from the half-equivalence point and estimate the concentration of the analyte by the volume of acid used to reach the equivalence point. Such titration curves can be used to identify unknown substances or determine the purity of a sample.

Acid-base neutralization is the underlying chemical process in a titration. It involves the reaction between an acid and a base to produce water and a salt. In the case of titrating a weak base with a strong acid, the acid's protons (H⁺) react with the base's ions or molecules to form the conjugate acid of the weak base. This neutralization reaction is crucial because it gradually removes the basic nature of the solution until the equivalence point is reached.

At the equivalence point, theoretically, the number of acid moles equals the number of base moles, and the solution has no net acidic or basic properties. However, because the resultant salt's cation can often slightly interact with water (a process known as hydrolysis), the pH at equivalence for weak base-strong acid titrations falls below 7.