The study of molecular interactions of ascorbic acid and sodium ascorbate with water at temperatures (278.15, 288.15 and 298.15) K

Highlights: • Density, speed of sound, viscosity and refractive index of important vitamins are reported. • Molecular interactions of ascorbic acid and sodium ascorbate in water have been studied. • Vϕ0 and B-coefficient of solutes studied show the presence of strong solute–solvent interaction. • These interactions strengthened at higher temperatures. • Ascorbic acid and sodium ascorbate act as a water structure destroyer (Chaotropes). -- Abstract: The article reports experimental values of density (ρ), speed of sound (u), viscosity (η) and refractive index (nD) for the binary systems, (L-ascorbic acid + water) and (sodium ascorbate + water) over the concentration range (0.01 to 0.75) mol · kg−1 at temperatures (T = 278.15, 288.15 and 298.15) K. From these experimental results, apparent molar volume (Vϕ) of solute, isentropic compressibility of solution (κS), apparent molar isentropic compressibility (κϕ) of solute and relative viscosity of solution (ηr) have been calculated. The limiting apparent molar volume (Vϕ0) of solute, limiting apparent molar isentropic compressibility (κϕ0), limiting apparent molar expansivity (Eϕ0) of solute, coefficient of thermal expansion (α∗) and hydration number (nH) of water soluble vitamins have been obtained. The experimental values of relative viscosity were used to calculate Falkenhagen coefficient A and Jones–Dole coefficient B. The transition state theory has been used to calculate the Gibbs free energy of activation of viscous flow per mole of solvent (Δμ10numbersign) and per mole of solute (Δμ20numbersign). The related activation parameters like ΔS20numbersign and ΔH20numbersign have also been calculated. From the results obtained, a discussion was carried out in terms of interactions and structure factor (in the framework of "structure-making" and "structure-breaking" solutes) in these binary mixtures