The question of which equilibria will occur in the solution to determine the pI depends on thermodynamic and kinetic feasibility. Based on these factors, the autoprotolysis of HA (the fourth equilibrium) is likely to dominate, followed by the acidic and basic reactions of HA (the first and second equilibria, respectively). The third equilibrium, which involves the interaction between HA and H3O + , is the least likely to occur and can be excluded from further consideration (see Appendix D). The fifth equilibrium, governing the autoionization of water, operates in any aqueous solution by default, ensuring that the product of the concentrations of H3O + and OH -remains constant at a given temperature (e.g., 10 -14 at 25°C) . However, it does not directly affect the pI of glycine.