log10Ka3

log10Ka3 refers to the base-10 logarithm of the third dissociation constant (Ka3) of a polyprotic acid. Polyprotic acids are substances that can donate more than one proton (H+) per molecule. For a triprotic acid, there are three dissociation steps, each with its own equilibrium constant. Ka1 represents the first dissociation, Ka2 the second, and Ka3 the third. The equilibrium constant for a dissociation step describes the ratio of the concentration of products to reactants at equilibrium.

Ka3 specifically quantizes the equilibrium of the final proton dissociation step from a species that already has lost two protons. The expression for Ka3 for a generic triprotic acid H3A is: Ka3 = ([HA2-][H+]) / [A3-]. Taking the base-10 logarithm of this constant, log10Ka3, is often used because the resulting values are typically much smaller and easier to manage, especially in calculations involving pH and the relative concentrations of different species in solution. Similar to Ka1 and Ka2, a larger log10Ka3 value indicates a stronger tendency for the acid to donate its third proton, meaning the conjugate base A3- is a weaker base. The log10Ka values are frequently tabulated and used in chemical education and research to predict the behavior of polyprotic acids in aqueous solutions.