| In this paper, a proton transfer reaction that has contributions to the proton balance equation (PBE) is called the basis acid-base equilibrium, and a new method for obtaining the pH value of the solution is established. In a solution, there are usually two or more basis acid-base equilibria. In a specific concentration range, the contributions of one or more basis acid-base equilibria to PBE can be negligible, and one or more components in the material balance equation can sometimes also be ignored, which is the theoretical foundation for the approximate calculation of pH of the solution. In H2C2O4 (oxalic acid) solution, when the concentration c?√(K_a1 K_a2 ), H2O+H2C2O4?H3O++HC_2 O_4^- is the dominant acid-base equilibrium, the pH calculation can be treated as a weak monoprotic acid (Ka1); When c ?√(K_a1 K_a2 ), the pH behavior of H2C2O4 solution is similar to that of sulfuric acid (H2SO4), the first dissociation of H2C2O4 is close to complete ionization. The new method has the advantages of simplicity, applicability to various acidic and alkaline substances, a different concentration range corresponds to a different pH formula. The introduction of the concept of the basis acid-base equilibrium can help us obtain new pH formulas and gain a clear insight into the physical meanings of various pH formulas, update new understandings of shift of chemical equilibria, change of the dominant acid-base equilibrium, pH calculations and other related knowledges. |
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