Raman spectroscopic study of effect of CaCl2 and MgCl2 on structure of water

Raman spectra of aqueous solutions of CaCl2 and MgCl2 in the OH stretching region (2 500 to 4 000 cm(-1)) with various concentrations below 1.0 mol (.) L-1 were measured. Computer deconvolutions of the Raman spectra allow the percent of tetrahedral hydrogen bonded structure of water to be determined. It is shown that CaCl2 and MgCl2 break tetrahedral hydrogen bonded structure of water and the breaking effect of Ca2+ is stronger than that of Mg2+. By comparision with results of O-17 NMR, it is deduced that CaCl2 and MgCl2 promote structure of water as a whole by forming hydrogen bondings among water molecules with fewer hydrogen bondings even though they break tetrahedral hydrogen bonded structure of water.