Abstract:

There are several proton transfer reactions and multiple chemical equilibria in NaHCO₃ aqueous solution. As the concentration of the solution changes, the contents of H₂CO₃, H⁺, OH⁻ and CO₃²⁻, which are related to proton transfer reactions, also change. The diagram of [H₂CO₃], [H⁺], [OH⁻] and [CO₃²⁻] with solution concentration c is plotted. From the diagram, we can directly observe which species are the major and which are the minor. In a high concentration, [H₂CO₃] ≈ [CO₃²⁻] > > [OH⁻] > > [H⁺], indicating that the proton reactions which can produce H⁺ or OH⁻ are negligible, and HCO₃⁻ + HCO₃⁻$ \rightleftharpoons $ H₂CO₃ + CO₃²⁻ is the dominant. In 9.1 × 10⁻⁶ mol∙L⁻¹ solution, [OH⁻] ≈ [H₂CO₃] > > [H⁺] ≈ [CO₃²⁻], indicating that H₂O + HCO₃⁻ $ \rightleftharpoons $ H₂CO₃ + OH⁻ is the dominant. In an extremely dilute solution, [OH⁻] ≈ [H⁺] > > [H₂CO₃] > [CO₃²⁻], indicating that H₂O$ \rightleftharpoons $ H⁺ + OH⁻ dominates.

Key words: NaHCO₃ solution, Multiple chemical equilibria, Dominant reaction, Diagram for the contents of the reaction products