Abstract
An improved fully automatic controlled system for calorimetry has been employed with the aim at studying relatively weak complex formation equilibria in solutions. Complex formation reactions between zinc(II) and thiocyanate ions have been investigated in an aqueous solution containing 5mol dm-3 NaClO4 as a constant ionic medium at 25°C. Calorimetric titration curves obtained were well explained in terms of formation of the [Zn(NCS)n](2-n)+ (n=1-4) complexes, and the formation constants and enthalpies of formation of the complexes have been determined. The stepwise enthalpy and entropy values at the second step of formation of the [Zn(NCS)2] complex were more positive than those at other steps, which suggested that water molecules solvating the metal ion were extensively liberated at the second step.
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