ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2009, Vol. 83, No. 10, pp. 1737–1746. © Pleiades Publishing, Ltd., 2009. 1737 INTRODUCTION Studies on density, viscosity and acoustic proper- ties of ionic solutions are of great help in characteris- ing the structure and properties of solutions. Various types of interactions exist between the ions in the solu- tions and of these, ion–ion and ion–solvent interac- tions are of current interest. These interactions [1–4] help in better understanding of the nature of solute and solvent, i.e., whether the added solute modifies or distorts the structure of the solvent. Recently we have undertaken a comprehensive program to study the sol- vation and association behavior of some electrolytes [4–8] in different aqueous and non-aqueous solvent media from the measurement of transport and ther- modynamic properties. Formamide (FA) is choosen for the study as it is a simplest amide that contains a peptide linkage, the fundamental building block of proteins [9]. It along with some of its derivatives serves as good solvents for many organic and inorganic com- pounds and is also used as a plasticizer. Hence, in the present study, we reported density, viscosity and ultrasonic speed of ammonium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, zinc sulfate, and cadmium sulfate in 10, 20 and 30 wt % formamide + water mixture at 298.15, 308.15, and 318.15 K and the derived parameters were discussed in terms of ion–ion and ion–solvent interactions. EXPERIMENTAL Extrapure grade Formamide procured from S.d.fine-Chem. Limited, India was purified by the standard procedures [10]. After purification its purity was ascertained by GLC and also by comparing exper- imental values of densities and viscosities with their literature values [11–14]. The physical properties of pure and aqueous binary mixtures of formamide at dif- ferent temperatures are listed in Table 1. All the sulfate salts (Anal R grade) were procured from E. Merck (India) Ltd. They were used after drying over P 2 O 5 in a desiccator for few hours. The reagents were always placed in the desiccator over P 2 O 5 to keep them in dry atmosphere. Freshly distilled conductivity water (specific conductance <10 –6 Ω –1 cm –1 ) was used for preparing aqueous mixtures of formamide. The densities (ρ) were measured with an Ostwald– Sprengel type pycnometer having a bulb volume of 25 cm 3 and an internal diameter of the capillary of about 0.1 cm. The pycnometer was calibrated at 298.15, 303.15, and 308.15 K with doubly distilled water and benzene. The pycnometer with the test solu- tion was equilibrated in a water-bath maintained at ±0.01 K of the desired temperatures. The pycnometer Apparent Molar Volume, Viscosity, and Adiabatic Compressibility of Some Mineral Sulfates in Aqueous Binary Mixtures of Formamide at 298.15, 308.15, and 318.15 K 1 M. N. Roy, R. Chanda, and B. K. Sarkar Department of Chemistry, University of North Bengal, Darjeeling-734013, India e-mail: mahendraroy2002@yahoo.co.in Received July 28, 2008 Abstract—The densities and viscosities of several sulfates, viz., ammonium sulfate, sodium sulfate, potas- sium sulfate, magnesium sulfate, zinc sulfate and cadmium sulfate in aqueous binary mixtures of formamide (FA) have been determined at 298.15, 308.15, and 318.15 K and at atmospheric pressure. The ultrasonic speeds of the electrolytic solutions have also been measured at 298.15 K. Apparent molar volumes (φ V ), vis- cosity B-coefficients and adiabatic compressibilities (K S ) of these electrolytic solutions were calculated from the experimental densitiy, viscosity and acoustic data. The density and viscosity data were evaluated by using Masson’s and Jones–Dole equation respectively; the derived parameters have been analyzed in terms of ion– ion and ion–solvent interactions. The structure making/breaking capacities of the electrolytes have been inferred from the sign of . The results showed that all the electrolytes act as structure-makers in these media. Also the compressibility data indicated electrostriction of the solvent molecules around the cat- ions. The activation parameters of viscous flow were also determined and discussed by the application of tran- sition state theory. DOI: 10.1134/S0036024409100203 ∂ 2 φ V 0 / ∂ T 2 ( ) P PHYSICAL CHEMISTRY OF SOLUTIONS 1 The article is published in the original.