Potentiometric titration and equivalent weight of humic acid

Geochimica et Cosmochimica Acta
By:  and 



The “acid nature” of humic acid has been controversial for many years. Some investigators claim that humic acid is a true weak acid, while others feel that its behaviour during potentiometric titration can be accounted for by colloidal adsorption of hydrogen ions. The acid character of humic acid has been reinvestigated using newly-derived relationships for the titration of weak acids with strong base. Re-interpreting the potentiometric titration data published by Thiele and Kettner in 1953, it was found that Merck humic acid behaves as a weak polyelectrolytic acid having an equivalent weight of 150, a pKa of 6.8 to 7.0, and a titration exponent of about 4.8. Interdretation of similar data pertaining to the titration of phenol-formaldehyde and pyrogallol-formaldehyde resins, considered to be analogs for humic acid by Thiele and Kettner, leads to the conclusion that it is not possible to differentiate between adsorption and acid-base reaction for these substances.

Publication type Article
Publication Subtype Journal Article
Title Potentiometric titration and equivalent weight of humic acid
Series title Geochimica et Cosmochimica Acta
DOI 10.1016/0016-7037(60)90136-8
Volume 20
Issue 1
Year Published 1960
Language English
Publisher Elsevier
Description 15 p.
First page 30
Last page 44
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