Study of electrolytic dissociation by the Raman effect. II.—Nitrates

Abstract

In the first part of these investigations by the author, the possibility of studying electrolytic dissociation by the Raman effect has been described with special reference to nitric acid. Accurate quantitative estimation has since been made of the degree of dissociation in the acid by measuring the intensities of Raman lines corresponding to the dissociated NO¯ 3 ions at various concentrations. The results thus obtained indicated that the dissociation in nitric acid is progressive between the concentrations 1-16 N and not complete as has been assumed for highly dilute solutions. A comparison of the values of the degree of dissociation obtained from this method with those calculated from conductivity measurements revealed a large discrepancy which was attributed to the uncertainty of the latter. The degree of dissociation cannot be directly evaluated from the values of electrolytic conductivity, which depend upon a number of factors such as viscosity of the solution, mobility of the ions, etc., as there is much uncertainty as to the dependence of conductivity on such factors. With Raman spectra, however, the number of molecules or ious is directly proportional to the intensity of the Raman lines corresponding to them. Hence a comparison of the number of molecules or ions at one concentration with that in another is made by simply comparing the intensities of the lines corresponding to them in the Raman spectra taken with the respective concentrations. The accuracy of the method is that attainable in the intensity measurements. Thus we have in this method a reliable means of measuring electrolytic dissociation, and another advantage is its applicability to concentrated solutions, for which at present no theory has been fully developed. In order to determine whether electrolytes are completely dissociated even in concentrated solutions, a systematic study of different electrolytes is being undertaken. The results for nitrates will be described in this communication.