Apparent molar heat capacities and apparent molar volumes of Hg(ClO 4) 2(aq) and Pb(ClO 4) 2(aq) at 298.15 K

Abstract

We have made calorimetric and densimetric measurements on aqueous solutions of Hg(ClO 4) 2 and Pb(ClO 4) 2 in dilute HClO 4 at 298.15 K. Results are expressed as “experimental” apparent molar heat capacities and apparent molar volumes, which include contributions from the aqueous metal perchlorate solutes and from the perchloric acid. We have used Young's rule to assess and subtract the contribution of HClO 4 from these “experimental” apparent molar properties to yield apparent molar heat capacities and apparent molar volumes for (Hg 2+ + 2ClO 4 −)(aq) and (Pb 2+ + 2ClO 4 −)(aq). From these heat capacities and volumes we have calculated partial molar properties at infinite dilution for these metal perchlorate solutes. The partial molar heat capacities and partial molar volumes at infinite dilution were found to be −16 J · K −1 · mol −1 and −14.2 cm 3 · mol −1 for Hg 2+(aq) and −56 J · K −1 · mol −1 and −17.8 cm 3 · mol −1 for Pb 2+(aq), respectively. We have compared these values for Hg 2+(aq) and Pb 2+(aq) with those calculated from semi-empirical correlations.