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2006
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December
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In the Laboratory
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Advanced Chemistry Classroom and Laboratory
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Studying Fast Reactions: Construction and Use of a Low-Cost Continuous-Flow Instrument
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Patrick J. Bisson and James E. Whitten
Department of Chemistry and Center for Advanced Materials, University of Massachusetts Lowell, Lowell, MA 01854
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December 2006
Vol. 83 No. 12
p. 1860
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| Abstract |
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The design, construction, and use of a low-cost continuous-flow instrument for studying the kinetics of fast reactions in the student laboratory is described. In this method, reagents mix, react, and flow through a reaction tube. If one of the reagents or products absorbs visible light, a traveling photometer may be used to measure absorbance along the length of the tube. This transforms the time progression of the reaction to space and permits fast reactions to be studied, since a small interval in time can be stretched out over an arbitrarily large distance by adjustment of the flow velocity in the tube. While this is a well-known method in chemical kinetics, it is not commonly used in the teaching laboratory owing to the expense of purchasing a commercial instrument. By using a light-emitting diode light source and a photodiode-on-a-chip detector, it is possible to construct a traveling photometer from a minimal number of components. A novel feature of the described instrument is a position sensor consisting of a high resistance iron–nickel alloy wire across which a dc voltage is applied. The traveling photometer makes electrical contact with the wire as it moves along the length of the reaction tube, and the voltage it encounters is proportional to position. A two-channel computer interface is used to simultaneously measure absorbance and position. The performance of the instrument has been evaluated by studying the reaction of crystal violet with sodium hypochlorite. Under the conditions used, this reaction is complete within two seconds. Use of the instrument demonstrates that the reaction is first order with respect to each reactant with a room temperature rate constant of 63 M-1s-1.
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| Supplement |
A complete set of drawings that may be submitted to a machine shop, photographs of the apparatus, and a student handout are available.
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| More Information |
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Citation |
Bisson, Patrick J.; Whitten, James E. J. Chem. Educ. 2006 83 1860.
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Keywords |
Hands-On Learning / Manipulatives; Kinetics; Laboratory Equipment / Apparatus; Laboratory Instruction; Physical Chemistry; Rate Law; Reactions; Spectroscopy; Upper-Division Undergraduate; UV-Vis Spectroscopy
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History |
Created:
Last Updated: |
10/30/2006
11/7/2006
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 Caution! | | 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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2006
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