The behaviour of electrolytes in mixed solvents. Part V.–The free energy of lithium chloride in water-alcohol mixtures and the salting-out of alcohol

Abstract

In Part II of this series of papers are recorded measurements of the partial vapour pressures of solutions of lithium chloride in water-ethyl alcohol mixtures, the alcohol contents of which extended from 6•4 to 100 mols. per cent. It has seemed desirable to extend this range so as to include some smaller concentra­tions of alcohol, and accordingly measurements have now been made of solutions containing 2 and 4 mols. per cent, of alcohol and in each case 0.5, 1.0 and 4.0 m. lithium chloride. The experimental method was the same as that previously described, except that in these cases the viscosity method was less suitable for determining the composition of the condensate, which was obtained by comparison with known compositions in the interferometer. The final values of the partial pressures, each being the mean of at least two deter­minations, are given in Table I. αw/αw0 and αa/αa0 are the relative activities, i. e., the ratio of the partial pressure in a given solution to the partial pressure of the corresponding solvent. Two of the solutions containing 6.4 mols. per cent, alcohol were also redetermined and gave values in close agreement with those previously obtained. We are now in a position to discuss in more detail the behaviour of these solutions. It was shown in the previous paper that while the salt increased the partial pressure of alcohol in solutions containing smaller proportions of alcohol, it caused a lowering of the pressure in the more alcoholic solutions, but the relative lowering of the vapour pressure of alcohol was always less than that of water, indicating that in all solutions the alcohol was salted out with respect to the water. In order to assess this effect more precisely it is necessary to consider what will be the behaviour of a solute which interacts equally with the two solvent molecules.