# Are there separate quantity symbols for the pKa of a substance and the pKa of its conjugate acid? Tags: acid-base, nomenclature - Score: 8 - Views: 378 - Answers: 1 - Answered: yes - Asked by: Karsten (44753 rep) - Asked: 2022-01-23 - Edited: 2022-01-23 - Site: chemistry ## Question For polyprotic acids, we distinguish the different deprotonation equilibria and their equilibrium constants by indices, e.g. phosphoric acid dissociation is described by $K_1$, $K_2$, and $K_3$. Considering the acid/base properties of water, there are two relevant equilibria (protonating or deprotonating water once) and equilibria with at least two other species ($\ce{H4O^2+}$ and $\ce{O^2-})$. Is there a systematic nomenclature for these equilibria, maybe something like $K_1$, $K_2$, and $K_{-1}$ and $K_{-2}$? In tables (typically in organic chemistry), molecules are often listed alongside with the $\mathrm{p}K_\mathrm{a}$ values of the conjugate acid, e.g. comparing the basicity of amines and amides. There is potential confusion with the $\mathrm{p}K_\mathrm{a}$ values of the species listed (giving a measure of how acidic they are). Is there are good way of symbolically distinguishing the $\math