Student exploration of the Henderson-Hasselbach equation and pH readings to determine the pK a value of 4,4′-trimethylenedipiperidine (TMDP)

Abstract This educatory experiment uses an inexpensive pH meter to determine an approximate negative logarithm of the acid dissociation constant (p K a ) value of 4,4′-trimethylenedipiperidine (TMDP). Using a pH meter and statistical data analysis by Excel tool presents an excellent opportunity to deepen student engagement with the Henderson-Hasselbalch equation and acid/base dissociation constant ( K a / K b ). Furthermore, students understand the importance determination of K a / K b and its relationship with the concentration and strength of acid/base. Four different concentrations of TMDP aqueous solutions were prepared and a series of pH readings were collected using a calibrated pH meter. Some statistical parameters were calculated and analyzed using the statistical program in Excel. Finally, students identified an unknown p K a for TMDP and compared their obtained value with a predicted p K a using software like ChemAxon. The experiment is inexpensive, safe, simple, and clean, and less experienced students can perform it. In addition, all pH recordings can be readily accessible for analysis and descriptive statistics by the Excel formula.