Compilation and Evaluation of Solubility Data in the Mercury (I) Chloride�Water System

The more than one dozen papers dealing with the solubility of mercury (1) chloride in water or in aqueous chloride solutions have been compiled in the format set by the IUPAC Solubility Data Project, and have been evaluated. Mercury (I) chloride dissolves in water, forming the following species: He(OH)₂, HgCl₂, HgOH⁺, HgOH⁺, HgCl⁺, Hg²⁺ ₂, and Hg₂OH^− in addition to H⁺ and Cl^−. In excess chloride solutions it dissolves to give, mainly, HgCl^− ₃ and HgCl^2− ₄. Thus, many homogeneous equilibria have to be considered beside the two heterogeneous ones; Hg₂Cl₂(s)=Hg²⁺ ₂(aq)+2Cl^−(aq) and Hg²⁺ ₂(aq)=Hg²⁺(aq)+ Hg(l), of which K^° _s0 and (K^° _r)^−1, respectively, are the equilibrium constants. The papers in which the total solubility (sum of all the mercury containing aqueous species) and the solubility product (derived from e.m.f. data) are reported do not give as accurate and reliable quantities as are obtained from the appropriate standard electrode potentials. The following values are recommended as valid at 298.15 K: log (K^° _s0/mol²kg^−2=−17.844±0.017, d log (K^° _s0/mol²kg^−2)/dT?0.0002)−(6.0±0.4)×10^−1 (T/K−2.98.¹⁵), ΔG^° _s0=101.86±0.10 kJ mol^−1, ΔS^° _s0=−12.7±0.9 JK^−1 mol ^−1. ΔH^° _s0 =98.08±0.18 kJ mol^−1, ΔC^° _p,s0=−0.36±0.04 JK^−1 mol^−1 (this item, tentatively), and c_Hg?1.6)×10^−6 mol dm^−3 (the total aqueous solubility).