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Potentiometric titration of polyuronic acids

R. Kohn

Institute of Chemistry, Slovak Academy of Sciences, 809 33 Bratislava


Abstract: Using ion-exchange technique it was possible to prepare clear dilute solutions of polyuronic acids which, to the present, were considered insoluble or sparingly soluble materials. Potentiometrie titrations of polymannuronic, polyguluronic, pectic, and polymethacrylic acid with potassium and calcium hydroxide were investigated. The titration of clear solutions of polyuronic acids with alkali hydroxides can be well expressed by the extended Henderson and Hasselbalch equation up to the degree of dissociation a = 0.80 (n = 1.6—1.7). Neutralization of the studied poly acids with calcium hydroxide proceeds in the manner similar to that of weak monobasic acids (n = 1) which is due to the suppression of electrostatic effects of carboxylate group caused by Ca2+ ions. Small deviations were found only when pectic and polyguluronic acids were titrated with calcium hydroxide in which case the neutralization was accompanied by partial coagulation of corresponding calcium polyuronates. Apparent dissociation constants found for polyuronic acids are compared with dissociation constants of the corresponding monouronic acids.

Full paper in Portable Document Format: 272a218.pdf


Chemical Papers 27 (2) 218–226 (1973)

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