Abstract:
In periodic precipitation (Liesegang banding), the overwhelmingly common trend is the increase in spacing between consecutive bands as we move away from the interface. Revert spacing is a rare trend observed in a few systems, wherein the spacing decreases with distance from the interface. In this Letter, we compare the spatial profiles of the aqueous components in two chromate Liesegang precipitates: CuCrO4 and PbCrO4, displaying direct and revert spacing, respectively. The profiles are measured using UV-Vis spectrophotometry. The formation of a Pb2+-PbCrO4 complex in equilibrium with the free Pb2+, seems to play a key role in the revert spacing scenario. © 2013 Elsevier B.V. All rights reserved.