Ionic interaction in alkali metal hydroxide solutions — A raman spectral investigation

Abstract

Raman spectral investigations made on concentrated solutions of potassium and sodium hydroxides in water, and on potassium hydroxide solution in methyl alcohol have confirmed the presence of clusters in these solutions. These clusters arise due to association between K + or Na + ion and OH − ion. The increase in temperature of the alkali metal hydroxide solution or the addition of hydroxide of zinc or aluminium to it leads to the dissociation of these clusters. This dissociation is responsible for the increase in the solubility of zinc oxide at room temperature when the solutions are prepared from the hot alkali metal hydroxide solutions. The dissociation further helps in the understanding the higher solubility of hydroxides of zinc and aluminium in concentrated alkali metal hydroxide solutions as compared to the corresponding oxides. The discrepancy in Raman studies on aluminate ions in concentrated akali metal hydroxide solutions and the nonlinear variation of refractive index of alkali metal hydroxide solution with concentration have also been explained on the basis of observed ion-pair association in these solutions.