engleski

Raman spectra of aqueous solutions of strong electrolytes: evolving-factor analysis

Ion association in aqueous solutions of varied concentrations of LiNO3, Mg(NO3)2, Co(NO3)2, Li2SO4 and MgSO4 was studied by means of Raman spectrometry assisted by principal-components (PCA) and evolving-factor (EFA) analyses. Formation of one Raman-active associated species, {;M...L(R)}; (M = Li+, Mg2+, Co2+ ; L = NO3-, SO42-), was detected at higher salt concentrations (>2 mol/L for LiNO3, >1 mol/L for Co(NO3)2, >0.2 mol/L for Li2SO4, >0.5 mol/L for MgSO4). Spectral profiles of L(aq) and {;M...L(R)}; species were computed by means of EFA, as well as their equilibrium concentrations in each solution. Maximum fractions of anions engaged in {;M...L(R)}; species amounted (at highest salt concentrations) to 0.6 (LiNO3), 0.4 (Co(NO3)2), 0.60 (Li2SO4) and 0.3 (MgSO4). Since, for a given salt concentration, the equilibrium concentration of Raman-active species, [M...L(R)], was always lower than the concentration of analogous UV-active species, [M...L(UV)] (reported in a previous paper) it is suggested that {;M...L(UV)}; could be a precursor of {;M...L(R)};. In all instances, apparent stability constants of {;M&#61626 ; L(R)}; species, falling into the range of (0.01 < K1/dm3 mol-1 < 1), have a progressively upward trend with increasing salt concentration.

ion association ; Raman spectrometry ; principal component analysis ; evolving factor analysis

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