Structure of aqueous solutions. Infrared librational band study of structure making and structure breaking by dissolved electrolytes

Abstract

The concentration dependence of the infrared libration band of water has been studied for forty-six electrolytes and normalised first and second band moments have been calculated. Changes in the band parameters give information on both making and breaking of the hydrogen bonded water structure. For salts containing oxyanions, hydrogen bonding between water and the anion is shown to be important with the influence becoming more pronounced with larger cations due to cooperative action. Acids and alkalis all produce a reinforcement of the hydrogen bound structure of water but the structure reinforcement is not spatially extensive and structure breaking by the anion is also observable. The structure change which is reflected in movement of the normalised first band moment is found to correlate well with solution entropy values for monatomic ions. For solutions containing polyatomic ions the solution entropy apparently contains a contribution from anion orientation effects. The changes in spectral band parameters have been used to calculate solution viscosites in the concentrated solution range. The calculated values are comparable with previous best calculations and enable the contribution of various solvent–solute interactions to viscous flow to be evaluated.