Limitations to Acid-Base Titrations

In an acid–base titration the volume of titrant needed to reach the equivalence point is proportional to the moles of titrand. Because the pH of the titrand or the titrant is a function of its concentration, however, the change in pH at the equivalence point—and thus the feasibility of an acid–base titration—depends on their respective concentrations. The illustration below, for example, shows a series of titration curves for the titration of several concentrations of HCl, each 25 mL in volume, with equimolar solutions NaOH: (a) 10^–1 M HCl, (b) 10^–2 M HCl, (c) 10^–3 M HCl, (d) 10^–4 M HCl, and (e) 10^–5 M HCl. For titrand and titrant concentrations smaller than 10^–3 M, the change in pH at the end point is too small to provide accurate and precise results.