Open AccessThe behaviour of electrolytes in mixed solvents. Part. III.–The molecular refractivities and partial molar volumes of lithium chloride in water-ethyl alcohol solutions
Author(s) -
J. A. V. Butler,
A. D. Lees
Publication year - 1931
Publication title -
proceedings of the royal society of london. series a, containing papers of a mathematical and physical character
Language(s) - English
Resource type - Journals
eISSN - 2053-9150
pISSN - 0950-1207
DOI - 10.1098/rspa.1931.0060
Subject(s) - chemistry , alcohol , solvent , lithium chloride , chloride , inorganic chemistry , electrolyte , ethyl iodide , aqueous solution , lithium (medication) , iodide , lithium nitrate , organic chemistry , ionic bonding , ion , medicine , electrode , endocrinology
It is well known that the molecular refractivity of most salts, as calculated by the Lorentz-Lorenz formula, is nearly independent of the concentration in moderately dilute aqueous solutions. Walden determined the refractivities of tetra-ethyl-ammonium iodide and other similar salts in a variety of solvents and found that, while the molecular refractivity was approximately independent of the concentration in each solvent, it varied from one solvent to another, the greatest variation from the value in water, amounting to about 2 per cent., being obtained in nitro-methane, Schreiner has recently determined the molecular refractivity of hydrogen chloride and lithium chloride in methyl and ethyl alcohols, and found that in the case of lithium chloride the value is independent of the concentration up to a concentration of about 3 M. His values for R18 D for lithium chloride are: 8.73 in water, 8.55 in methyl alcohol and 8.38 in ethyl alcohol. The difference between the values in water and ethyl alcohol appeared to make it just possible to determine the variation of the refractivity with the composition of the solvent in mixtures of water and the alcohol. It is possible that a solvent might he found, miscible in water in all proportions, in which the value of It is further removed from that in water. Such a substance would he more suitable than alcohol for the investigation of this effect, but in order to correlate the results with the measurements recorded in Part II of the activities of alcohol and water in water-alcohol-lithium chloride solutions, it seemed desirable to investigate this case in the first instance. The variation of the refractivity of a salt with the composition of a mixed solvent may be expected to give some indication of the composition of the solvent in the immediate vicinity of the ions. For the refractivity of a salt is determined by (1) the polarisability of the ions themselves and (2) the change in the polarisability of the solvent produced by their presence. The molecular refractivity of a salt in a solution containingm grams of a salt inw grams of the solvent is taken as R = M/m (n 2 -1/n 2 + 2 .w +m /d -n 2 0 -1/n 2 0 + 2 .w /d 0 (1) wheren , andd andn 0 ,d 0 are the refractive index and density of the solution and of the solvent, respectively, and M the molecular weight of the salt.