Concentrated potassium zincate solutions studied using laser Raman spectroscopy and potentiometry

Abstract

The results of a study of the nature of the concentrated potassium zincate solutions in alkali are reported. Data from several independent but complementary techniques are mutually consistent and show that electrolytically produced solutions of high concentration are relatively complex, the complexity depending upon the age. It is concluded that initially quasi-colloidal particles, based on Zn(OH)₂ and molecules of solvation, are present. The particles of colloidal character are electroinactive and undergo a first order decay to yield a solution containing the species [Zn(OH)₂·2H₂O], [Zn(OH)₃·H₂O]^– and [Zn(OH)₄]^2–, the actual constitution depending on the concentration.

It is shown that previous spectral assignments are erroneous, reported bands at 283 and 310 Δcm^–1 arising from the KOH solution itself. The new data show the non-colloidal zinc species to be tetrahedral, and not planar or octahedral.

It was found that the ν₁ band (Raman) of Zn(OH)^2–₄ occurred at 471.2 ± 0.9 Δcm^–1(previously accepted value ∼484 Δcm^–1).

The 430 Δcm^–1 value for ν₃ was confirmed but the expected, weak ν₂ and ν₄ bands were not detectable due to the high background and overlapping KOH solution bands.