The paper considers using a high-sensitivity calorimeter with an isothermal jacket to measure heat capacities of electrolyte salt solutions at the temperature of 298.15 K, the salt being sodium iodide NaI dissolved in isopropyl alcohol and in mixtures of isopropyl alcohol with water containing 10, 20, and 40 % water by mass, at various molalities of the electrolyte salt. We processed the apparent heat capacity values computed for the electrolyte salt by means of the ion association model, which assumes that there exists an equilibrium between ions and ion pairs of the same type in a solution. The association constant values obtained make it possible to predict the heat capacity values not measured empirically, which lie within the margin of error of the experimental values. The investigation shows that the apparent heat capacity of the electrolyte salt as a function of concentration is adequately described by the ion association model in a wide range of solution molalities
Calorimeter with an isothermal shell was used at a temperature of 298.15 K to measure the following parameters: enthalpy of NiSO4(k) dissolution in water followed by generation of two molar concentration solutions; enthalpy of four NiSO4 aqueous solutions dilution having various molar concentrations followed by generation of solutions with approximately the same concentration values. Based on the data obtained, enthalpy and ion association constant in the NiSO4 aqueous solution, as well as standard enthalpy of the aqueous solution formation, were determined for the indicated compound. The latter value made it possible to establish a more accurate value of standard enthalpy in the Ni2+ cation formation in an aqueous solution, which turned out to be equal to --52.3 ± 0.5 kJ/mol.
The authors used E.M. Kuznetsova's theory to derive an equation for computing thermal capacity of an electrolyte in a dissociated solution. This equation may also be used to determine such important characteristics as the constant and enthalpy of ion association in electrolyte solutions. This equation is derived from the simplest model, that of ion association, which allows certain solution properties to be adequately described as functions of concentration. The ion association model is based on the equilibrium between ions and ion pairs of the same kind that exists in electrolyte solutions
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