Making pH calculations in the titration of strong protolytes

Abstract

Titration graphs of protolytic systems are very useful among other things to find the equivalence point (ep), choose the most suitable indicator, calculate the titration error and decide whether a given titration is feasible or not under certain conditions. The main feature of a titration curve is the pH jump that occurs in the vicinity of the equivalence point. Titration graphs can be obtained experimentally using the potentiometric method with the pH electrode. They also can be obtained theoretically by plotting the pH dependence equation with the added titrant volume or with the titrated fraction. In this exercise, we propose the pH calculation for two points in the titration of strong protolytes (HCl solution vs. NaOH solution). Some features of the titration curves involving these protolytes are presented together with some simple instructions for drawing by hand these curves and with the use of a spreadsheet (interactive graphs). Two final exercises of self-evaluation are proposed.