The complexes of Cr(3+) ion formed by 8-hydroxyquinoline (HQ, HL) and 8-hydroxyquinoline-5-sulfonic acid (HQ-5-SA, H(2)L) were investigated by means of potentiometry and spectroscopy at 25.0 +/- 0.1 degrees C and in ionic strength of 0.1 M KNO(3) and 0.1 M KCl, respectively. Over the acidic pH range, the coordination of Cr(3+) ion to HQ and HQ-5-SA in 1:1 mole ratios occur, CrL(2+) and CrL(+) type complexes are formed. At near neutral pH, CrL(OH)(+) and CrL(OH) type hydroxo complexes formed. All the data can be explained with the formation of only binary and mixed hydroxo Cr(3+) complexes of these ligands. The formation constants were determined using the BEST computer program in 0.1 M KNO(3) ionic medium. The stoichiometries of Cr(3+) complexes formed with these ligands were defined and their formation constants were determined. Thus, the removing capacities of these ligands could be examined by calculating the equilibrium concentration of Cr(3+) that exists in the discharge water of various industries since Cr(3+) ions are the main pollutants present during waste water treatment in Bursa city of Turkey.