Influence of water microimpurities on acetone structure: Volume effects of H2O and D2O solvation

Abstract

Here, we report the limiting partial molar volumes of ordinary water (H 2 O) and heavy water (D 2 O) in acetone and the excess molar volumes of these mixtures derived from precision density measurements at T = 288.15‐318.15 K and p ≈ 0.1 MPa. We have found the following. In the presence of water microimpurities (with water mole fractions up to 0.03), the molecular packing of acetone acquires a greater expansibility due to the appearance of new structural fragments (solvate complexes) in which bonding is stronger than in the bulk of the solvent. This weakens acetone‐acetone interactions and loosens the initial solvent structure as a whole; the effect is especially noticeable for the limiting dilution of acetone solutions of heavy water. We discovered the nontrivial fact that the negative (in sign) isotope effect on the limiting partial molar volume of water dissolved in acetone increases considerably with rising temperature. Acetone of high purity grade (from Khimmed; no more than 0.008 wt % water according to Fisher’s test) was used in experiments. Bidistilled water of the natural isotope abundance (electrical conductivity σ ≈ 1.3 × 10 –5 S/m) and heavy water D 2 O (from Izotop; 99.92 ± 0.02 wt % D) (based on density [3]) were used to prepare solutions. The solutions were prepared by a gravimetric method by diluting the degassed host solvent accurate to 2 × 10 ‐5 c sm,2 units, where c sm,2 is the solvomolality of the water isotopologue. Solvomolality c sm,2 is a dimensionless parameter of the solution compositions expressed through