Abstract:

The study of acid-base equilibrium constitutes an important component of the contents in the Analytical Chemistry subject offered in various university science degree programs. This study involves several fundamental objectives, including the comprehension of pH calculation, the determination of final volumes and errors in acid-base titrations, and estimation of the displacement of complex formation, solubility and redox equilibria, in the presence of secondary reactions, such as protonation of anions, the formation of metal-hydroxyl complexes, and/or precipitation of hydroxides. These concepts often present notable challenges for students. Typically, these deficiencies emerge during pre-university levels of education and persist at the university level when not adequately addressed. Furthermore, this issue becomes particularly serious for students with insufficient mathematical and chemical skills. For this reason, it is interesting the development of methodologies that simplify the resolution of complex problems, such as pH calculation, in order to enhance comprehension and provide greater autonomy in problem-solving among students.

In this study, the acid-base equilibrium is approached through the use of protonation equilibrium constants. In the context of this equilibrium, dissociation constants are found in tabulated form. The use of these constants in the charge balance results in mathematical expressions for molar fractions that can be difficult to remember, requiring deduction by the student. On the contrary, using protonation constants (the inverses of dissociation constants) yields mathematical expressions that can be associated to mnemonic rules. The use of protonation constants makes the mathematical treatment more accessible to students with limited mathematical preparation and improves their results, as it will be shown. The objective is to ensure that any student in Chemistry or Analytical Chemistry can easily engage in problem-solving in a more simplified manner.

Keywords:

Acid-base equilibrium, Analytical Chemistry, Simplification of calculations, Undergraduate students, University.