Modeling Oxygen Solubility in Water and Electrolyte Solutions

A model is presented for estimating oxygen solubility in water and solutions of inorganic electrolytes (I) as a function of oxygen pressure PO2 (atm), temperature T (K), and I. It is based on a thermodynamic analysis for water, where the molal concentration caq of oxygen follows an equation of the form caq = PO2k and k is a T-dependent function (equilibrium constant) related to the chemical potential, entropy, and partial molar heat capacity of the gaseous oxygen (O2)g and dissolved oxygen (O2)aq species. In the presence of I, the oxygen solubility becomes (caq)I = φcaq, where φ is a modifying factor < 1 that is dependent on I and its molal concentration CI. The decreasing molar heat capacity of (O2)aq with rising T, which affects k, is discussed. The decrease in φ with increasing CI is related in a general way to the decrease in partial molar volume of the water.