Calculation of stoichiometric dissociation constants of monoprotic carboxylic acids in dilute aqueous sodium or potassium chloride solutions and p[m(H + )] values for acetate and formate buffers at 25 o C

Add time:09/30/2019    Source:infona.pl

Equations are given for calculation of the stoichiometric (molality scale) dissociation constants, K m , of weak acids in dilute aqueous electrolyte solutions at 298.15 K from the thermodynamic dissociation constant, K a , of the acid and the ionic strength, I m , of the solution. The equations for K m were based on the single-ion activity coefficient equations of the Huckel type. The equations were tested with the conductivity data for formic, acetic, propionic, n-butyric, lactic, chloroacetic, α-crotonic and cyanoacetic acids, and with data measured by Harned cells for formic, acetic, propionic, n-butyric and glycolic acids. These data were taken from the literature. According to these tests, K m can be obtained by the Huckel method within experimental error at least up to I m of about 0.1 mol kg - 1 . On the basis of the equations for K m , it is suggested p(m H ) values {p(m H )=-lg[m(H + )/(mol kg - 1 )] where m refers to the molality} for buffer solutions containing acetic or formic acid. A new calibration method is suggested for glass electrode cells, and this method is based on the p(m H ) values instead of pH values (pH=-lg[a(H + )] where a refers to the activity).

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