Modeling oxygen solubility in water and electrolyte solutions

A model is presented for estimating oxygen solubility in water and solution s of inorganic electrolytes (I) as st function of oxygen pressure P-O2 (atm ), temperature T (K), and I. It is based on a thermodynamic analysis for wa ter, where the molal concentration c(aq) of oxygen follows an equation of t he form c(aq) = Po(2)k and k is a T-dependent function (equilibrium constan t) related to the chemical potential, entropy, and partial molar heat capac ity of the gaseous oxygen (O-2)(g) and dissolved oxygen (O-2)(aq) species. In the presence of I, the oxygen solubility becomes (c(aq))(I) = phi c(aq), where phi is a modifying factor < 1 that is dependent on I and its molal c oncentration C-I. The decreasing molar heat capacity of (O-2)(aq) with risi ng T, which affects k, is discussed. The decrease in phi with increasing C- I is related in a general way to the decrease in partial molar volume of th e water.