ACTIVITY-COEFFICIENTS IN (ELECTROLYTE PLUS AMINO ACID)(AQ) - THE DEPENDENCE OF THE ION ZWITTERION INTERACTIONS ON THE IONIC-STRENGTH AND ONTHE MOLALITY OF THE AMINO-ACID ANALYZED IN TERMS OF PITZER EQUATIONS

Activity coefficients for NaCl in aqueous solutions containing a varia ble molality of NH2CH2CO2H (glycine) were obtained from the e.m.f.s of the galvanic cell: Na-glass \NH2CH2CO2H (m(A)), NaCl (m(B)), AgCl\Ag, at different ionic strengths. They were fitted to a modified Pitzer e quation by taking into account that the ion-zwitterion interactions de pend on both the ionic strength and the zwitterion molality of the sol ution. Standard deviations for the fittings of about the same size as the accepted experimental uncertainty (+/-0.10 mV, i.e. +/-0.0008 in l g gamma+/-) were found by neglecting the ion-zwitterion-zwitterion and ion-ion-zwitterion interactions. Activity coefficients for NH2CH2CO2H in these aqueous mixtures were thus calculated. They agree well with the literature values obtained for more dilute solutions.