engleski

Calibration of Glass Electrode in Terms of H+ Concentration by Titration of Weak Acid in Cells With and Without Liquid Junction

Calibration of glass electrode cells with and without transference in terms of hydrogen ion concentration was performed by potentiometric titrations of aqueous solutions of two weak acids, Tris hydrochloride and potassium hydrogenphthalate, with a strong base (KOH). Cell calibration parameters were computed from the titration data, along with the values of stoichiometric protonation equilibrium constants, by using an iterative optimisation procedure. No significant difference between the E vs. [H+] responses of the glass-electrode cells with and without liquid junction was observed. For both kinds of cell, the imposed model of linear E vs. p[H] relation proved to be a satisfactory approximation only in the buffer regions of the titration curves. The values of protonation equilibrium constants, expressed as lg(K1H/dm3 mol– 1), determined at 25 °C, Ic = 0.1 mol dm 3 (KNO3 or KNO3 + KCl) in the cell with transference (Tris: 8.058, phthal2– : 4.933) are in very good agreement with those determined in the cell without transference (Tris: 8.091, phthal2– : 4.928), as well as with comparable literature values.

glass electrode calibration ; liquid junction ; p[H] ; potentiometric titration ; protonation constant ; potassium hydrogenphthalate ; 2-amino-2-hydroxymethyl-1 ; 3-propanediol (Tris)

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