Fitting and Analyzing pH Titration Curves on a Graphing Calculator

The pH titration curve is a well-known figure in chemistry. It is easy to plot this graph from experimental data by measuring pH as a function volume of added titrant; however, there is no simple mathematical equation for expressing pH as a function of titrant volume. The logistic function has been suggested but, as discussed in this paper, it is inadequate for modeling titration curves. Developed in this paper is a piecewise continuous function (with chemically meaningful parameters) of pH versus volume. A program has been written to display this function on a graphing calculator. This program can be used by students (1) to analyze the characteristics of pH titration curves, for example, the derivative and the presence of two inflection points, and (2) to interactively fit experimental titration data that they have collected.