Thermal diffusion of dilute aqueous Na2MgEDTA and Na2CaEDTA solutions at 25°C

The Soret effect in dilute aqueous solutions (0.01–0.1m) of Na₂MgEDTA and Na₂CaEDTA is investigated using the flow-cell method. The Soret coefficients obtained from thermal diffusion experiments conducted at 25°C are reported. Heats of transport have been estimated based on the Debye-Hückel theory and the molar entropies of transport, calculated. Results of the present work have been compared with the Soret data for MgCl₂ and CaCl₂. It is suggested that the solvent exchange effect may account for the differences in the Soret effect observed between the pairs (Mg⁺², Ca⁺²) and (MgEDTA^–2, CaEDTA^–2).