Structure of water in solutions in the subcooled region from freezing-point depressions

Abstract

Hydrogen-bond structural temperatures were estimated for water in solutions of NaCl, Na₂SO₄, MgCl₂ and MgSO₄ for a wide concentration range and down to –21 °C. These temperatures are proportional to the molality, the constant of proportionality being a function of the intrinsic volumes and the charges of the ions. The differences in the volumes and entropies of ice and water in the solutions have been calculated and a constant-volume entropy identified. This entropy is a linear function of the solute concentration and has a value around 0.15 J g^–1 K^–1 at zero concentration. Possible origins of this entropy for pure water are considered.