Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

Experimental densities of mixed aqueous solutions of sodium and potassium salts have been compared with the densities calculated for various alternative models to show that Na⁺ ion (in contrast to bulkier cations K⁺, Rb⁺, Cs⁺) is present as a NaH₂O⁺ particle analogous to hydroxonium ion H₃O⁺. The experimental data also suggest that apparent molar volumes of ions in aqueous solutions depend on the degree of „filling" of the solution with the ion volumes, or otherwise, on volume fraction of the water left in the solution for formation of electrostatically bound hydration sheaths of the ions. The observed increase of apparent volumes of electrolytes with their concentration is due to degradation of these close-packed hydration sheaths with decreasing proportion of water in the system.