IUPAC - composite alkalinity (09038)

composite alkalinity

symbol:

A_{P}

synonym: phenolphthalein end-point alkalinity

https://doi.org/10.1351/goldbook.09038

Measurement by titration to the phenolphthalein end-point (pH 8.3) of that portion of alkalinity arbitrarily attributed to all the hydroxyl content and half the carbonate content of a titrand.

Notes:

For the carbonate system, with no other oxoanions, $A_{P} = [CO_{3}^{2 -}] + [OH^{-}]$ where the concentrations refer to the solution before the titration $CO_{3}^{2 -} + H^{+} ⟶ HCO_{3}^{-}$ and $OH^{-} + H^{+} ⟶ H_{2} O$ performed to discoloration of the visual indicator.
By definition, composite alkalinity is zero for solutions which have a pH value of 8.3 or less.

Source:
PAC, 2025, 97, 137. (Glossary of terms for mass and volume in analytical chemistry (IUPAC Recommendations 2024)) on page 2 [Terms] [Paper]

Citation: 'composite alkalinity' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.09038 RIS BibTex EndNote

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composite alkalinity