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  Home > JCE Print > Journal of Chemical Education > Issues > 2009  > November  >
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In the Laboratory
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

Cover
November 2009
Vol. 86 No. 11
p. 1326

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.

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Citation
Heavers, Richard M.; Colucci, Liza A. J. Chem. Educ. 2009, 86, 1326.
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Keywords
Chemical Engineering; Demonstrations; Environmental Chemistry; Hands-On Learning / Manipulatives; Laboratory Instruction; Lasers; Liquids; Physical Chemistry; Physical Properties; Second-Year Undergraduate; Solutions / Solvents; Student-Centered Learning; Transport Properties; Undergraduate Research; Upper-Division Undergraduate
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History
Created:
Last Updated:
9/16/2009
9/25/2009
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Experiments, laboratory exercises, lecture demonstrations, and other descriptions of the use of chemicals, apparatus, instruments, computers, and computer interfaces are presented in the Journal of Chemical Education as illustrative of new or improved ideas or concepts in chemistry instruction and are directed at qualified teachers. Although every effort is made to assure and encourage safe practices and safe use of chemicals, the Journal of Chemical Education cannot assume responsibility for uses made of its published materials. Many chemicals are hazardous. Precautions for the safe use of hazardous chemicals and directions for their proper disposal are described in the Material Safety Data Sheets and on the labels. We strongly urge all those planning to use materials from our pages to make choices and to develop procedures for laboratory and classroom safety in accordance with local needs and situations.
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