pH Titration Curves

No pH titrations were carried out. Only simple titrations using an indicator to signal an endpoint were performed—with the single aim of determining the concentration of an acid or base solution.

Students perform titrations in which the pH is measured as a function of the added titrant. The experimental focus is now on examining a number of titration curves to identify types of acids and bases used (at least four unknowns). Students also determine quantities such as the pH at any endpoint(s) and pK values in any buffer regions.

Until 2005, the titrations have been carried out as pH versus time, with titrant added at a steady rate. The x axis in this case is proportional to the volume, so all the usual features are readily observed, but the actual volumes are unknown. We are now adding drop counters, so actual volumes will be automatically determined in future titrations.

A slight improvement in precision would be possible by performing the titration manually, collecting individual pH values for many titrant volumes each read from a buret. Such an experiment is tedious, however, and requires much more time than the 15 minutes or so needed to produce a printed titration curve using MeasureNet as described. At the University of Cincinnati, we prefer exposing the students to a range of acid-base systems while having time to discuss them and answer questions.