{"term":{"id":"09038","title":"composite alkalinity","longtitle":"IUPAC Gold Book - composite alkalinity","doi":"10.1351\/goldbook.09038","code":"09038","status":"current","synonym":"<em>synonym<\/em>: phenolphthalein end-point alkalinity","definitions":[{"id":1,"text":"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":{"1":"For the carbonate system, with no other oxoanions, \\(A_{\\rm{P}} = [\\ce{CO3^{2-}}] + [\\ce{OH-}]\\) where the concentrations refer to the solution before the titration \\(\\ce{CO3^{2−} + H+ -> HCO3−}\\) and \\(\\ce{OH− + H+ -> H2O}\\) performed to discoloration of the visual indicator.","2":"By definition, composite alkalinity is zero for solutions which have a pH value of 8.3 or less."},"links":[{"term":"alkalinity","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/09034"},{"term":"titrand","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/09051"}],"sources":["PAC, 2025, 97, 137. 'Glossary of terms for mass and volume in analytical chemistry (IUPAC Recommendations 2024)' on page 2 (https:\/\/doi.org\/10.1515\/pac-2023-0903)"]}],"altoutputs":{"html":"https:\/\/goldbook.iupac.org\/terms\/view\/09038\/html","xml":"https:\/\/goldbook.iupac.org\/terms\/view\/09038\/xml","plain":"https:\/\/goldbook.iupac.org\/terms\/view\/09038\/plain"},"citation":"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. 10.1351\/goldbook.09038","license":"The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/) for individual terms.","collection":"If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org .","disclaimer":"The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.","accessed":"2026-05-08T23:31:32+00:00"}}