THE MIDPOINT METHOD FOR PH CALCULATION: A SIMPLE AND PRACTICAL APPROACH FOR UNDERGRADUATE STUDENTS

The study of acid-base equilibria constitutes an important part in the contents of Analytical Chemistry or related subjects, which are imparted in different Science Degrees. One of the basic objectives of this study is the calculation of pH, which becomes usually difficult for students, especially for those with insufficient mathematical and chemical skills. The implementation of the new Science Degrees in the frame of the European Higher Education Space provides for the maintenance of the study of acid-base equilibria by promoting a higher degree of student’s self learning. For this reason, the development of simple methodologies that facilitate the resolution of complex problems, will simplify the understanding and solution of acid-base equilibria. In this sense, an intuitive approach for pH calculation (the midpoint method) is presented. With this method, pH calculation is reduced to finding the central point in a segment where the endpoints are easily established after drawing a linear predominance diagram, and locating the region where the solute is predominant. The method is suitable for students and professionals without requiring special mathematical and chemical skills or for situations where a rapid estimation of the pH is required, since the calculation time will never exceed a few seconds.