Spectrophotometric Studies of Cerium(III) Chelate of 7‐Iodo‐8‐Hydroxyquinoline‐5‐Sulphonic Acid

Cerium(III) chelate of 7‐iodo‐8‐hydroxyquinoline‐5‐sulphonic acid(ferron) has been studied spectrophotometrically in aqueous solution at 25°C and at an ionic strength of 0.1 M . The formation of this chelate was p H dependent, and the optimum p H range was between 5.5 to 6.0. Its mole ratio of ligand to cerium(III) ion was found to be 2 to 1 stoichiometry and the formation constant, log K , was determined as 10.15. Enthalpy and entropy changes characterizing the formation of the chelate have been calculated as follows: ΔG° =‐13.85 kcal mole ‐1 , ΔH°= −5.03 kcal mole ‐1 , ΔS°=29.56 eu mole ‐1 . By using the wavelength of 370 nm , determination of trace amount of cerium(III) ion with the sensitivity of 0.056   τ/cm   2was possible.