Thermodynamics of Cu(II)-Chromotrope-2R Chelate in Aqueous Medium

Chemical Laboratories, Birla Institute of Technology and Science, Pilani (Rajasthan)

(Manuscript received 10 February 1972; revised 7 June 1972; accepted 10 November 1972)

The composition, stability and thermodynamic parameters of the chelate formed between Cu(II) and phenylazochromotropic acid (Chromotrope 2R) has been investigated spectroplioto­metrically in aqueous medium. The red-violet chelate has ʎ_max at 580 nm against a reagent blank. The composition as determined by different methods is 1 : 1 at pH = 6.0±0.1. The mean value of log K and free energy of formation of the chelate are found to be 4.56±0.1 and —6.24±0.2 kcal/ mole respectively at 25°C. The enthalpy change (∆H) and entropy change (∆S) calculated by van't Hoff's isochore and Gibbs-Helmholtz equations are —17.92±0.02 kcal/mole and —39.82±0.02 e.u. respectively.