Spectrophotometric Determination of the Dissociation Constant of an Acid-Base Indicator Using a Mathematical Deconvolution Technique

Abstract

A laboratory experiment that uses a spectrophotometric method to determine the apparent acid-dissociation constant (K a') 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 K a′ 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.

Determination of Dissociation Constants of Malonic Acid in (Ethylene Glycol-Water)X% Mixed Solvent at Different Temperatures Using Electromotive Force Measurements

“…Intermolecular hydrogen bonding did not take place in the mono substituted malonic acid [4]. There are four General methods for the measurement of dissociation constant of carboxylic acid, including Potentiometric titration method [5] [6] [7] [8], Conductometric method [9][10] [11], Spectrophotometric methods [12] [13] [14], and Electromotive force measurement method [15][16] [17]. There are many studies on dissociation constant of carboxylic acid in different organic-water mixed solvents and at different temperatures [18] [25].…”

Determination of the Acid Dissociation Constant of a Phenolic Acid by High Performance Liquid Chromatography: An Experiment for the Upper Level Analytical Chemistry laboratory

“…Many experiments are reported for the undergraduate teaching laboratory that describe the use of potentiometric and spectrophotometric methods − for the determination of the acid dissociation constant. There are limited reports using HPLC.…”

Determination of the pKa Value of Phenolphthalein by Means of Absorbance Measurements

“…While there have been several experimental articles published in education papers applying spectroscopy to determine the pKa of acid-base indicators [10,11], the present article addresses the question of how to give stu-dents laboratory experience with limited equipment and space.…”