A chelating ion-exchange resin, Rhom and Haas Amberlite IRC 748, was investigated for the exchange of copper and sodium from aqueous solutions at four different temperatures. A two-parameter temperature-dependent, semiempirical thermodynamic ion exchange model was used to describe binary systems involving the ions Cu2+, Na+, and H+. To ensure that all experiments were conducted on purely binary systems, the resin was preconditioned into the hydrogen form. All experiments were conducted with Cl- as the nonexchanging anion and at temperatures of 4.0, 12.0, 20.0, and 40.0 +/- 0.1 degrees C. The semiempirical thermodynamic ion exchange model was shown to predict the shape of the equilibrium ion exchange curves accurately, despite the low concentrations of copper used in this study (0.001 57-0.007 87 N). There was a consistent increase in selectivity of the resin toward copper with an increase in temperature.