Kosmotropic and chaotropic behavior of hydrated ions in aqueous solutions in terms of expansibility and compressibility parameters

Abstract

Hydrated ions have fundamental applications in chemical and biological processes. Kosmotropic and chaotropic nature of hydrated ions affect the water structure in solutions depending upon their hydrophobicity or hydrophilicity nature. In present study Kosmotropic and chaotropic behavior of hydrated ions have been explained in terms of volumetric and acoustic parameters like apparent molar volume ( V ϕ ), expansibility and compressibility factors for aqueous electrolytic solutions provide useful information about interactions among ions and water molecules. Results of V ϕ showed that SO 4 2− ions due to stronger H-bonding with water molecules are termed as kosmotropes while Cl − and HCO 3 – are chaotropes due to their weaker H-bonding with water molecules. More compressible structure of solutions in the presence of SO 4 2− ions indicated its kosmotropic behavior and comparatively less compressible structure of solutions in the presence of Cl −1 and HCO 3 – ions renders them chaotropes. Results obtained from expansibility factor showed the dominance of electrostatic interactions over hydrophobic hydration of ions at higher temperatures. Greater values of expansibility factor for SO 4 2− ions as compared to Cl −1 and HCO 3 – ions renders them kosmotropic ion while later are termed as chaotropes. Hence, thermo-acoustic parameters could be effectively used to describe the hydrogen bonding character of ionic solutions in terms of kosmotropic and chaotropic behavior of solutions.