Analysis Of Potentiometric Titration Of Weakly Basic Anionites Curves
ANALYSIS OF POTENTIOMETRIC TITRATION OF WEAKLY BASIC ANIONITES CURVES
A. V. Mamchenko, L. G. Chernova
A.V. Dumanskii Institute of Colloidal Chemistry
and Water Chemistry NASU, Kyiv, Ukraine
Analysis of experimental potentiometric titration of weakly basic anionites of various classic curves has been made from the position of exchange equilibrium theory. On the basis of material balance and classical equation of Henderson-Hasselbalch there were determined effective or averaged dissociation constant (pK) and constant n. For the each ionite there were obtained two potentiometric titration curves when natrium chloride concentration differed more than two orders in external solution concentration. The reference of chloride-ions activities allow to combine them satisfactory.
Systematic deviation from an ideal behaviour observed for polystyrenedivilbenzene anionite Lewatit MP 62 are analogous with carboxyl cationites with rigorously indentical chemical composition of exchange groups. Those deviations are being described within the limits of exchange equilibrium theory. It was established experimental data for anionites with exchange groups of the same type were described by classical Henderson-Hasselbalch equation rather good. Anionites on the basis of acrylic matrix (Amberlite IRA 67) were subject to the ideal exchange model in gel phase. The introduction of quaternary ammonium basis (Lewatit AP 49) fixed ions into composition leads to the typical essential deviations of the experimental data from linear dependence in coordinates of generalised Henderson-Hasselbalch equation. Qualitative correlation have been obtained between the structure of the anionite-exchange resins and the shape of the titration curves followed from polyfunctionality of exchange groups. Comparative analysis potentiomertric tiration weakly basic acryl anionite Amberlite IRA 67 and strongly basic AB 17-8 curves offered to make assuming that classical equation of Henderson-Hasselbalch with various effective equalibrium constants, but the same values
of constant n could be satisfied in gel phase of anionite Lewatit AP 49 with the mixture of strongly and weakly basic groups for each form.
The equation for calculation of the quantity of strongly and weakly basic groups of acrylic anionite has been obtained. It was proposed an explanation of rare phenomenon of ideality of weakly dissociating (basic) and strongly dissociating (salt) rezinates of weakly basic acrylic anionites.
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