Aqueous Ammonia Equilibrium Calculations: Effect of pH and Temperature

The toxicity of ammonia to fishes has been attributed to the un-ionized ammonia chemical species present in aqueous solution. Because the percent of total ammonia present as un-ionized ammonia (NH₃) is so dependent upon pH and temperature, an exact understanding of the aqueous ammonia equilibrium is important for toxicity studies. A critical evaluation of the literature data on the ammonia–water equilibrium system has been carried out. Results of calculations of values of pK_a at different temperatures and of percent of NH₃ in aqueous ammonia solutions of zero salinity as a function of pH and temperature are presented.