Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

ABSTRACT

Isobaric volumetric heat capacities of aqueous solutions of K4Fe(CN)6, K3Fe(CN)6, K3Co(CN)6, K2Ni(CN)4, and KAg(CN)2 have been measured at 298.15 K over the approximate concentration range 0.02 to 0.4 molkg-1 using a Picker flow calorimeter. These data were combined with measured densities to calculate the corresponding apparent molar isobaric heat capacities, Cp. The values so obtained were fitted as a function of concentration using an extended Redlich-Rosenfeld-Meyer type equation to provide the standard state (infinite dilution) quantities, C po , for each salt. The Cp values for all the salts studied showed similar dependences on concentration, with a slight upward curvature at higher molalities, possibly due to anion aggregation. Values of C po for the aquated cyanometallate anions were estimated using the tetraphenylphosphonium tetraphenylborate extrathermodynamic assumption and were little affected by ion size but were strongly dependent on ionic charge, ranging from -191 J*K-1*mol-1 for [Fe(CN)6]4-(aq) to +178 J*K-1*mol-1 for [Ag(CN)2]-(aq). This indicates that the differences between the anions are mostly due to their effect on the surrounding water molecules.