Apparent molal volumes of some highly charged electrolytes in water

Abstract

The apparent molal volumes of Mg₂Fe(CN)₆, Sr₂Fe(CN)₆ and K₃Co(CN)₆ were measured at 25°C by pyknometric and dilatometric methods. The 2:4 salts appreciably deviate from the theoretical limiting law in a direction which is opposite, in the more dilute solutions, to that predicted by Debye–Hückel theory (DH). For K₃Co(CN)₆ no appreciable deviations from the theoretical slope are seen below 0.01 mol dm^–3 and the deviations are in the same direction as DH predicts when the concentration is increased. Such behaviour is similar to that of Ca₂Fe(CN)₆ and K₃Fe(CN)₆.

The results are analysed by means of the Mayer theory and by numerical integration of the Poisson–Boltzmann equation. Both treatments can justify, in terms of electrostatic interaction, volumetric behaviour similar to those of Mg₂Fe(CN)₆ and Sr₂Fe(CN)₆ for the 2:4 salts and to that of K₃Co(CN)₆ for the 1:3 salts.