 Glycolate

Glycolate, also called hydroxyacetate, is the conjugate base of glycolic acid. Its connectivity is $\mathrm{HOC}{\mathrm{H}}_2\mathrm{CO}{\mathrm{O}}^{-}$, with molecular formula ${\mathrm{C}}_2{\mathrm{H}}_3{\mathrm{O}}_3^{-}$ and net charge $-1$. ChEBI explicitly distinguishes this anion from its neutral acid.^[ref]

Removing the carboxyl proton changes both hydrogen count and charge:The alcohol-like hydroxy group remains in the specified singly charged species. Formula bookkeeping must therefore distinguish the acid, the anion and a complete salt containing the anion.

For example, one monovalent positive counterion balances one glycolate, while a divalent positive counterion requires two. A nominal calcium glycolate formula is $\mathrm{Ca}({\mathrm{C}}_2{\mathrm{H}}_3{\mathrm{O}}_3{)}_2$. An original amount example with $1\mathrm{mmol}$ of that formula unit contains $2\mathrm{mmol}$ of glycolate units. Hydration or another salt form changes formula mass and sample composition, so the mass of the isolated anion is not a universal salt molar mass.

Acid–base equilibrium determines how much is present as glycolate. For a suitable dilute-solution model,At $\mathrm{pH}=\mathrm{p}{K}_a$ the two forms have equal modeled concentrations; one pH unit above gives a $10:1$ ratio and base fraction $10/11\simeq 0.909$. This relative example does not assign a numerical acid dissociation constant. Activities, ionic strength and other equilibria matter when the dilute approximation is inadequate.

The chemical identity is independent of whether the ion was prepared as a salt or produced by deprotonating the acid in solution. An analysis that measures total glycolic-acid-derived material must state whether its reported quantity includes both protonation states or specifically the glycolate anion.