Sugar Fingers and Double-Diffusive Convection

Richard M. Heavers
Department of Chemistry and Physics, Roger Williams University, Bristol, RI 02809
Liza A. Colucci
Watershed Protection and Development Review Department, City of Austin, Austin, TX 78704
J. Chem. Educ., 2009, 86 (11), p 1326
DOI: 10.1021/ed086p1326
Publication Date (Web): November 1, 2009

Abstract

Vertical convection cells ("fingers") develop at the interface between a horizontal layer of sugar solution above a slightly denser solution of ordinary table salt. These fingers occur primarily because the molecular diffusivity of sugar is less than that of salt. We describe a two- or three-hour laboratory experiment in which the contributions of salt and sugar to the densities of both layers are measured over time with a refractometer and from the rotation of polarized light in a laser beam. Initial densities for salt and sugar solutions are specified for the experiment and for a physical chemistry class demonstration in which the fingers are projected on a screen. An example of undergraduate research is also given.

Keywords (Audience):

Second-Year Undergraduate

Keywords (Domain):

Chemical Engineering

Keywords (Pedagogy):

Hands-On Learning / Manipulatives

Keywords (Subject):

Lasers
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History

  • Received: August 03, 2009

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