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Journal of Structural Chemistry

2016 year, number 5

Bulk Properties and Hydration Numbers of Components of Water-Salt, Water-Urea, and Water-Urea-Salt Systems

V.P. Korolev1,2
1Krestov Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russia
2Ivanovo State University of Chemistry and Technology, Ivanovo, Russia
Keywords: кажущиеся и парциальные объемы, гидратные числа, водные растворы, мочевина, соли натрия, apparent and partial volumes, hydration numbers, aqueous solutions, urea, sodium salts


With an increase in the concentration of additives the hydration numbers of compounds decrease. Thus, in the saturated 54.6 % solution, urea loses approximately 3/4 of the initial amount of water, forming an aquacomplex of the composition (NH2)2COxH2O. In a supersaturated 44% solution, the sodium chloride aquacomplex is dehydrated by 2/3, and in a supersaturated 67% solution, sodium sulfate is dehydrated by 5/6. The density of these solutions is 1.354¸1.360 g/cm3 (44 % NaCl) and 1.800¸1.849 g/cm3 (67 % Na2SO4). In the saturated urea solution, NaNO3, NaCl, and Na2SO4 complexes lose 53¸55 % of hydrate water. It is shown here that in the binary water-urea system, interactions somewhat increase the hydration number of the salts (structural hydration). The characteristic important in the structural aspect (density of hydration water) increases in a series of solutions of compounds: urea, NaNO3, NaCl, and Na2SO4. In the same series of additives, an excess volume of binary water-urea and water-salt systems becomes more negative.