Trivalent cationic Sc, Y and La chelates with 4-phenylazo-7-(2-arsonophenylazo)- chromotropic acid ligand have been investigated by spectrophotometric methods. The formed chelates have violet colour. The studies reveal that 1:1, 1:2 and 1:3 metal : ligand (M:L) chelates are formed in solutions. The determination of the three metal ions in pg/cm3 range is described. The trivalent Y ion has been successfully determined using spectrophotometric titration with EDTA. The Stability constants of the formed chelates have been determined applying spectrophotometric and potentiometric techniques. The composition of these chelates was confirmed by conductometric titration.