Structural specifics of the concentration dependence of sound velocity in aqueous solutions of electrolytes

The concentration dependences of sound velocity in aqueous solutions of ele ctrolytes are analyzed over a wide range of concentrations (with extrapolat ion to 100% salt). For many systems, the concentration dependence of the sq uare of sound velocity is linear up to the values corresponding to overcool ed salt melts. For these solutions, an expression for partial molar compres sibility of salts in infinitely dilute solutions (K) over bar (0)(2s), is d erived based on the additivity of the squares of sound velocities of the so lution components, where the salt component is an overcooled melt. For alka li halides, there is good agreement between the values of (K) over bar (0)( 2s) calculated in this way and the values obtained by extrapolation of the apparent molar compressibility in the low-concentration region using the co ncentration dependences of density and the solution compressibility coeffic ient. For systems of this type, where hydration is the dominant process, so und velocity in hydration shells and complex ion groups is constant (i.e., independent of concentration). The effects are interpreted in terms of the concept of redistribution of the "fixed" structural groups in two concentra tion zones of a solution, where 1) the hydration groups are built in the st ructure of water in a complementary way; 2) the fragments of hydration sphe res and the ionic clusters are united with each other in a complementary wa y.