Physicochemical data for arsenic speciation calculations, and the development and application of an equilibrium model were determined numerically and experimentally to simulate the speciation of arsenic and copper in aqueous sulfuric acid solutions. Results show that concentrations of dissolved species depended highly on temperature, acidity, and solution concentration. A range of species can be formed, depending on pH and temperature. In acidic solutions, the principal ones are: HSO4−, H+, Cu2+, CuSO4(aq), H3AsO3(aq), and H3AsO4(aq); arsenic ions are present in low concentrations. Association degrees increase with temperature and concentration, the solutes being partially dissociated. Calculations of metal solubilities, pH, and ionic conductivity showed good agreement with experimental data. The model can be applied to study the aqueous speciation in industrial copper hydrometallurgical solutions, as well as to define and to evaluate purification strategies for the treatment of industrial effluents.