DETERMINATION OF THERMODYNAMIC PARAMETERS AND EQUILIBRIUM-CONSTANTS FOR COMPLEXATION REACTIONS INVOLVING LANTHANON(III) IONS WITH 1,2-NAPHTHOQUINONE-2-SEMICARBAZONE-4-SULFONIC ACID (SODIUM-SALT) (NQS.4S)

The thermodynamic parameters and equilibrium constants of complexation reactions of 1,2-naphthoquinone-2-semicarbazone-4-sulphonic acid (sodium salt) (NQS.4S) involving lanthanon ions were evaluated by potentiometric estimation of [H+], in aqueous medium at various ionic strengths (0.02, 0.05, 0.10 and 0.20 M NaClO4) and at different temperatures (20, 30, 40 and 50 +/- 0.5-degrees-C). The nBAR and pL values calculated by the method of Bjerrum and Calvin, as modified by Irving and Rossotti, were used for the calculation of the equilibrium constants on an HCL Busy Bee PC/AT computer using the weighted least-squares method. The values of S(min) were also evaluated. The order of equilibrium constants was found to be Ho(III) > Dy(III) > Tb(III) > Y(III) > Eu(III) > Sm(III) > Gd(III) > Nd(III) > Pr(III) > Ce(III) > La(III). The thermodynamic parameters DELTA-G, DELTA-H and DELTA-S were also calculated at a fixed temperature (30 + 0.05-degrees-C) and ionic strength (0.10 M NaClO4).