Calibration of Glass Electrode in Terms of H~+ Concentration by Titration of Weak Acid in Cells with and without Liquid Junction

摘要

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,2-amino-2-hydroxymethyl-1,3-propanediol hydrochloride,TrisHCl,and potassium hydrogen-phthalate,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 Ig(K_1~H/dm~3 mol~(-1)),determined at 25 deg C,I_c = 0.1 mol dm~(-3) (KNO_3 or KNO_3 + KCl) in the cell with transference (Tris:8.058,phthal~(2-):4.933) are in very good agreement with those determined in the cell without transference (Tris:8.091,phthal~(2-):4.928),as well as with comparable literature values.