A thermochemical study on the hydrolysis of mercury(II) chloride and mercury(II) thiocyanate complexes

Abstract

The enthalpy changes for the formation in solution of the mercury(II) hydroxo chloride (HgClOH) as well as of the hydroxo thiocyanate (HgSCNOH) complexes have been determined, at 25·00°C in 1 M (Na +)ClO 4 − ionic medium, by a direct calorimetric titration procedure. By combining the heat measurements with the equilibrium constants obtained previously[1,2] the free energy, the enthalpy and the entropy changes associated with the formation of the mixed complexes have been evaluated. The results are summarized in Table 4. In the systems studied the enthalpy changes for ( 1 2 ) HgA 2+( 1 2 ) Hg(OH) 2⇆ HgAOH and for HgOH + + HgA +⇆HgAOH + Hg 2+ (A − = Cl −, SCN − are approx. 0, within the uncertainty of 1–2 kJ/mole. Thus the formation of the mixed complexes from the binary species depends mainly upon the entropy changes involved.