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The Chemical Educator

ISSN: 1430-4171 (electronic version)

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Abstract Volume 12 Issue 5 (2007) pp 335-337

A Simple Spectrophotometric Determination of an Equilibrium Constant That Does Not Require Any Measurements of pH, Mass, Volume, Concentration, or Molar Absorptivity: The pKa of Methyl Red

Jose C. Barreto*, Terry A. Dubetz, David W. Brown, and Patricia D. Barreto

Florida Gulf Coast University, Department of Chemistry and Mathematics, and The Whitaker Center for Math and Science Education, Fort Myers, Florida 33965,
Received July 24, 2006. Accepted June 2, 2007.

Published online: 14 September 2007

Abstract. This laboratory exercise is intended for first-year chemistry students. It is designed to determine the pKa of Methyl Red with good precision and accuracy, while eliminating the need for pH meters, balances, pipets, or multiple buffer solutions. The experimental design is intended to encourage data sharing in class, requires only simple and rapid calculations, and will generate some thought provoking results about the relationship between pH and pKa.

Key Words: Laboratories and Demonstrations; general chemistry; equilibrium; pKa; spectrophotometry; colorimetry; indicator

(*) Corresponding author. (E-mail:

Article in PDF format (158 KB) HTML format

Issue date: October 1, 2007

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