Dissociation constants of carboxylic acids at high ionic strengths

Dissociation constants (pK(a)) of acetic, oxalic, citric, and ethylenediaminetetraacetic acids have been determined potentiometrically using a hydrogen ion glass electrode at 25 degrees C in solutions of ionic strengths ranging from 0.3 to 5.0 m NaCl. The observed ionic strength dependencies of the pK(a) values have been described successfully over the entire ionic strength range using both the Specific Ion Interaction Theory and the Pitzer model. The variation of the pK(a) values at high ionic strengths with the type and concentration of supporting electrolyte is discussed and compared to literature data.