CONSTANT OF ELECTROLYTIC DISSOCIATION OF LITHIUM, SODIUM AND POTASSIUM SULPHATES IN AQUEOUS ETHANOL SOLUTIONS

Abstract

Constants of electrolytic dissociation of the lithium, sodium and potassium sulphates in aqueous ethanol solutions at 25 °C were determined by conductometric method. Li2SO4, Na2SO4, K2SO4 were shown to decrease their ability to dissociation. It is generally accepted that the degree of electrolytic dissociation of electrolytes in a solution depends on the dielectric constant of the solvent. Water and ethanol differ greatly in their dielectric constant. For this reason, it is possible to prepare the solvent with different dielectric permittivity by changing the alcohol content in a mixture with water, thus, influencing the equilibrium state of the salt in solution. Therefore, in water-ethanol solutions with an increase in the alcohol content, sulfates of lithium, sodium and potassium should exhibit the properties of a weak electrolyte. In this case, the dependence of the molar conductivity on the concentration of sulfates of lithium, sodium and potassium in water-ethanol solutions will have a different appearance. Indeed, with an increase in the alcohol content in aqueous ethanol solutions, the molar conductivity decreases due to a decrease in the degree of electrolytic dissociation. With a decrease in the salt concentration in the solution, the molar electrical conductivity increases, approaching λ0, for both water and water-alcohol solutions. As it follows from the obtained data, the dependence of λ on the total concentrations of Li2SO4, Na2SO4, K2SO4) for the water solution with a high correlation coefficient is transformed into a straight line in the coordinates of the Kolraush equation since the sulfates of lithium, sodium and potassium act as strong electrolytes in the aqueous medium. For water-ethanol solutions, a high correlation coefficient in the coordinates of the equation 4λ3· C0(M2SO4)2 = КDIS · λ03 - КDIS - λ02·λ is observed in the case of [C2H5OH]> 50% of the volume. This means that in these solutions lithium, sodium and potassium sulphates exhibit the properties of a weak electrolyte. When the alcohol content is from 10% to 40% by volume, sulfates of lithium, sodium and potassium are medium-strength electrolyte and, therefore, low correlation coefficients are characteristic of transformations in the coordinates of the equations Kohlrausch and 4λ3· C0(M2SO4)2 = КDIS · λ03 - КDIS - λ02·λ.