Sorption of hydrochloric and perchloric acids and their sodium salts was studied by Cl- and ClO4- forms of ion exchanger Dowex I x 8 in the concentration range of the external electrolyte 0.25-4 mol/l. Sorption of water and the total amount of the solution were also studied. Sorption of the acid appeared markedly higher than that of the respective salts. A mathematical modeling and computer simulation of the processes were performed. The overall sorption was represented as a superposition of the Donnan membrane distribution and formation associates type RAn (.) (AnKt)(i) (.) (H2O), in the homogeneous resin phase. The model expresses non-ideality of the resin phase in explicit form as formation of the above associates characterized by the constants of their formation. A good agreement between the experimental and calculated sorption in the whole concentration range was obtained in the assumption of two associates with i = 1, 2 and n = 1-3. The same factors control sorption of the acids and the salts and the difference in their behavior has a quantitative character. The main introduction into the overall sorption of the salts makes the Dorman distribution up to concentration of the external electrolyte 4 M, while the main part of the absorbed acids is contained in the associates. (C) 2004 Elsevier B.V. All rights reserved.