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The Chemical Educator

ISSN: 1430-4171 (electronic version)

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Abstract Volume 9 Issue 3 (2004) pp 166-171

Spectronic 20: Kinetic Evaluation of the Oxidation of Bromocresol Green

Joseph C. Phillips* and Daniel W. Harville

Brevard Community College, Science Department, Melbourne, FL 32935,
Received October 30, 2003. Accepted April 6, 2004.

Published online: 26 May 2004

Abstract. This paper utilizes the Spectronic 20 to optically determine the kinetics of the reaction between bromocresol green (designated HBCG) and bleach (designated ClO) as a function of concentration and temperature. The technique uses a crossover or intersection time, tx, of the percent transmission (%T) for the reaction and the predetermined percent transmission of a standard solution. This technique requires less data to be collected than other techniques thereby reducing the laboratory time for each experiment. The reciprocal of the crossover time for a first-order reaction is proportional to the rate and rate constant of the reaction. These results agreed rather favorably with the reported conventional visual-color-matching techniques. The reliability of the optical technique can be greatly enhanced by better controlling the experimental conditions for temperature fluctuations, mixing, and cuvette transfer rates.

Key Words: Laboratories and Demonstrations; analytic chemistry; instrumental analysis; UV–vis spectroscopy; dyes/pigments; redox reactions; kinetics

(*) Corresponding author. (E-mail:

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New file uploaded 8/6/2004. Figure cations 4, 5 and 6 corrected.

Issue date: June 1, 2004

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