Effects of dissolved electrolytes on the solubility and partial molar volume of helium in water from 50 to 400 atmospheres at 25°C

The solubility of helium in water and aqueous CsCl, NaCl and MgCl₂ solutions at concentrations up to 3.380 molal has been measured at 50 atm intervals from 50 to 400 atm at 25°C. Setschenow coefficients for helium are practically invariant with pressure in each solution, decrease significantly with increasing electrolyte concentration and vary with the type of electrolyte in a fashion identical to that observed for the low pressure solubilities of other gases. The pressure dependence of the helium solubility in each solution follows a form of Henry's law in which the helium partial molar volume at infinite dilution \(\bar V^{_{He}^o } \) is independent of pressure. Values of \(\bar V^{_{He}^o } \) , computed from Henry's law, are smaller for the electrolyte solutions than for water and vary systematically with the type and concentration of dissolved electrolyte. This result is explained qualitatively in terms of ion hydration and its influence on the ability of the intrinsic configurational volume in each liquid to accommodate the relatively small helium molecules. It is concluded that intrinsic solvent structure is an important factor governing the partial molar volume of helium and the pressure dependence of helium solubility in water and aqueous electrolytes.