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Research Letters in Physical Chemistry
Volume 2009 (2009), Article ID 350424, 4 pages
Research Letter

Spatial Heterogeneity and Imperfect Mixing in Chemical Reactions: Visualization of Density-Driven Pattern Formation

1Department of Chemistry, Hofstra University, Hempstead, NY 11549-1510, USA
2Department of Physics and Astronomy, Hofstra University, Hempstead, NY 11549-1510, USA

Received 16 February 2009; Accepted 3 April 2009

Academic Editor: Q. Xu

Copyright © 2009 Sabrina G. Sobel et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Imperfect mixing is a concern in industrial processes, everyday processes (mixing paint, bread machines), and in understanding salt water-fresh water mixing in ecosystems. The effects of imperfect mixing become evident in the unstirred ferroin-catalyzed Belousov-Zhabotinsky reaction, the prototype for chemical pattern formation. Over time, waves of oxidation (high ferriin concentration, blue) propagate into a background of low ferriin concentration (red); their structure reflects in part the history of mixing in the reaction vessel. However, it may be difficult to separate mixing effects from reaction effects. We describe a simpler model system for visualizing density-driven pattern formation in an essentially unmixed chemical system: the reaction of pale yellow F e 3 + with colorless S C N to form the blood-red Fe ( S C N ) 2 + complex ion in aqueous solution. Careful addition of one drop of Fe ( N O 3 ) 3 to KSCN yields striped patterns after several minutes. The patterns appear reminiscent of Rayleigh-Taylor instabilities and convection rolls, arguing that pattern formation is caused by density-driven mixing.