Ionic Strength Correction for Extent of Ammonia Ionization in Freshwater

Abstract

Previously published tabulations of percent ammonia ionization inherently define pH in terms of concentration (molality) rather than the measured entity, hydrogen ion activity. In hard waters this may result in overestimation of the un-ionized NH 3 concentration by 10–20%. The thermodynamic basis for current empirical methods for temperature correction is examined, and a tabulation of NH 3 ionization fraction as a function of pH, temperature, and dissolved solids, together with a corresponding predictive equation, is presented.