Apparent molal volumes and adiabatic compressibilities of aqueous transition metal chlorides at 25°C

The apparent molal (φ_V) volumes and adiabatic [φ_K(S)] compressibilities of aqueous solutions of some transition metal (Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, and Cd²⁺) chlorides in the molality range 0 ≤ m ≤ 1.0 have been determined from precise density and sound speed measurements at 25°C. φ_V and φ_K(S) have been extrapolated to infinite dilution with the aid of an extended Debye-Hückel equation. The infinite dilution partial molal (V⁰) volumes and compressibilities (K_s⁰) for the transition and alkaline earth metal ions have been used to examine the ion-solvent interactions. The electrostriction partial molal volumes, V̄⁰(elect) = V̄⁰(ion) - V̄⁰(int), and compressibilities, K̄⁰(elect) = K̄⁰(ion) - K̄⁰(int), yield values of 11.1 ± 1.5 and 8.2 ± 1.2, respectively, for the number of water molecules hydrated to the cations. Correlations of V̄⁰(elect) and K̄⁰(elect) with various properties (radius, hydration, enthalpy, entropy, and heat capacity) of the transition metal and group 2A ions show variations which appear to be related to the d orbitals, similar to other thermodynamic properties.