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  Home > JCE Print > Journal of Chemical Education > Issues > 2005  > June  >
In the Laboratory
Monitoring Particle Growth: Light Scattering Using Red and Violet Diode Lasers
Heejoon Ahn and James E. Whitten
Department of Chemistry and Center for Advanced Materials, The University of Massachusetts–Lowell, Lowell, MA 01854
Cover
June 2005
Vol. 82 No. 6
p. 909
Abstract
A physical chemistry laboratory light scattering experiment using 407-nm violet and 670-nm red diode lasers is described. The use of two wavelengths at the extremes of the visible spectrum to monitor the growth of colloidal sulfur particles provides a dramatic demonstration of the preferential scattering of violet light by small particles and intense scattering of red light as particle size increases. By simultaneously monitoring the intensities of the scattered 407- and 670-nm light with two photodiode detectors, the kinetics of the reaction of sodium thiosulfate with hydrochloric acid to form sulfur particles can be studied. This reaction is found to obey approximately first-order kinetics with respect to sodium thiosulfate when its concentration is varied in the presence of excess acid.

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*  Citation
 Ahn, Heejoon; Whitten, James E. J. Chem. Educ. 2005 82 909.
*  Keywords
 Colloids; Hands-On Learning / Manipulatives; Kinetics; Laboratory Equipment / Apparatus; Laboratory Instruction; Lasers; Physical Chemistry; Spectroscopy; Sulfur; Upper-Division Undergraduate
*  History
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Last Updated:		 April 27, 2005
May 11, 2005
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