Apparent molar heat capacities and apparent molar volumes of Y-2(SO4)(3)(aq), La-2(SO4)(3)(aq), Pr-2(SO4)(3)(aq), Nd-2(SO4)(3)(aq),Eu-2(SO4)(3)(aq), Dy-2(SO4)(3)(aq), Ho-2(SO4)(3)(aq), and Lu-2(SO4)(3)(aq) at T=298.15 K and p=0.1 MPa

The apparent molar heat capacities C degrees (p,phi) and apparent molar vol umes V degrees (phi) of Y-2(SO4)(3)(aq), La-2(SO4)(3)(aq), Pr-2(SO4)(3)(aq) , Nd-2(SO4)(3)(aq), Eu-2(SO4)(3)(aq), Dy-2(SO4)(3)(aq), Ho-2(SO4)(3)(aq), a nd Lu-2(SO4)(3)(aq) were measured at T = 298.15 K and p = 0.1 MPa with a So dev (Picker) flow microcalorimeter and a Sodev vibrating-tube densimeter, r espectively. These measurements extend from lower molalities of m = (0.005 to 0.018) mol . kg(-1) to m = (0.025 to 0.434) mol . kg(-1), where the uppe r molality limits are slightly below those of the saturated solutions. Ther e are no previously published apparent molar heat capacities for these syst ems, and only limited apparent molar volume information. Considerable amoun ts of the RSO4+(aq) and R(SO4)(2)(-)(aq) complexes are present, where R den otes a rare-earth, which complicates the interpretation of these thermodyna mic quantities. Values of the ionic molar heat capacities and ionic molar v olumes of these complexes at infinite dilution are derived from the experim ental information, but the calculations are necessarily quite approximate b ecause of the need to estimate ionic activity coefficients and other thermo dynamic quantities. Nevertheless, the derived standard ionic molar properti es for the various RSO4+(aq) and R(SO4)(2)(-)(aq) complexes are probably re alistic approximations to the actual values. Comparisons indicate that V de grees (phi){RSO4+ aq, 298.15 K} = -(6 +/-4)cm(3). mol(-1) and V(phi)degrees {R(SO4)(2)(-), aq, 298.15 K} = (35 +/-3) cm(3). mol(-1), with no significa nt variation with rare-earth. In contrast, values of C degrees (p,phi){RSO4 +, aq, 298.15 K} generally increase with the atomic number of the rare-eart h, whereas C degrees (p,phi){R(SO4)(2)(-), aq, 298.15 K} shows a less regul ar trend, although its values are always positive and tend to be larger for the heavier than for the light rare earths. (C) 2001 Academic Press.