The acid-base properties of analogous complex ions of chromium(III) and cobalt(III) in aqueous solution have been studied. The equilibrium constants for all metal complexes were determined by using potentiometric and spectrophotometric titration methods. First, dissociation constants for the studied complexes of Cr(III) and Co(III) were determined by means of the potentiometric titration method and using the STOICHIO computer programme. Then, pH-spectrophotometric titrations were performed and the OriginPro 7.5 computer programme was used to calculate the same constants. The measurements using both methods were carried out under the same conditions of temperature. T = 298.15 K, and over the same pH range 2.00-10.00, respectively. It turned out that the two methods used enabled us to obtain acidity constants in very good agreement. (C) 2008 Elsevier Ltd. All rights reserved.