Abstract:

Mass balance equation (MBE), charge balance equation (CBE), and proton balance equation (PBE) are commonly used in computations of chemical equilibria. This paper presented a proof that CBE can be derived from MBE, so it is not an independent equation. Although CBE is not a necessary condition, it is more efficient than MBE in chemical equilibria involving acid and base. The higher efficiency of CBE in this regard was found to be a variety of H⁺ sources. The conclusions are consistent with practical computations that MBE is the primary equation in computations of complexation, redox and precipitation equilibrium, whereas CBE is the primary equation in those of acid-base equilibrium. PBE is neither an independent equation, and only applicable in acid-base equilibrium; its function is completely and more efficiently implemented by CBE. So it is unnecessary to keep PBE in the textbook of quantitative analytical chemistry. This research clarifies the independent equation in chemical equilibria, which not only increases computation efficiency, but also makes the theoretical framework concise and clear.

Key words: Mass balance equation, Charge balance equation, Proton balance equation, Independent equation