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  Home > JCE Print > Journal of Chemical Education > Issues > 2005  > November  >
In the Laboratory
Spectrophotometric Determination of the Dissociation Constant of an Acid–Base Indicator Using a Mathematical Deconvolution Technique
Krystyn P. Alter, John L. Molloy, and Emily D. Niemeyer
Department of Chemistry, Southwestern University, Georgetown, TX 78626-6100
Cover
November 2005
Vol. 82 No. 11
p. 1682
Abstract
A laboratory experiment that uses a spectrophotometric method to determine the apparent acid-dissociation constant (Ka') of neutral red, a common acid–base indicator, has been developed. The experiment incorporates a unique data analysis technique using a mathematical deconvolution program that allows students to resolve distinct spectral components within complex absorbance spectra. After measuring the neutral red absorbance over a range of pH values, students quantify the acidic and basic forms of the indicator present in each solution, correct for differences in the molar absorptivities of each species, and determine the Ka′ of the indicator. This laboratory exercise gives students an opportunity to use advanced data analysis techniques and to observe directly how the spectral characteristics of an acid–base indicator are affected by the solution pH.
Supplement
Instructions for the students and notes for the instructor are available.
*  Contents JCE2005p1682W.doc (Microsoft Word)
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JCE2005p1682W.pdf

JCE2005p1682W.zip
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*  Citation
 Alter, Krystyn P.; Molloy, John L.; Niemeyer, Emily D. J. Chem. Educ. 2005 82 1682.
*  Keywords
 Acids / Bases; Analytical Chemistry; Computer-Based Learning; Hands-On Learning / Manipulatives; Instrumental Methods; Laboratory Instruction; Upper-Division Undergraduate; UV-Vis Spectroscopy
*  History
 Created:
Last Updated:		 9/22/2005
10/5/2005
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