Nitrophenol Violet as a New Tool for Studying of Kinetics of Reactions in Solutions

Abstract

This experimental lab set is for students taking college chemistry courses. It includes four laboratory works and completely illustrates the important parts of chemical kinetics, namely the determination of the rate constant and the determination of the factors influencing its value. They can be used in a laboratory set for a physical chemistry laboratory course, or separately, using only one or two of the four laboratory exercises for general, colloid, and organic chemistry laboratory courses, as well as biological and industrial catalysis. The experiment forms an understanding of the possibilities of controlling the reaction rate and an understanding of intermolecular interactions in solutions. The classical effects of the rate constant are considered, such as the effects of salt and solvent, as well as micellar catalysis. The main focus is on the following factors: increasing polarity of the medium or ionic strength decelerates the reactions between Dyez+ and HO– and accelerates that of Dyez– with HO–; solubilization of reagents by micelles of cationic, nonionic, and zwitterionic surfactants accelerates the reactions between Dyez+ and HO– and decelerates the reaction of Dyez– with HO–; anionic micelles decelerate both of them. Interest in micellar effects is due to both theoretical application in the study of reaction mechanisms, structure and dynamics of nanosized aggregates in solution, and practical application, for example, in organic synthesis, in industry. Quantitative data processing was carried out according to the Brønsted–Bjerrum and Scatchard equations, as well as linear dependences of solvation energies. The experiment also provides students with practical experience in using the spectrophotometer, as well as graphical and numerical analysis of the data obtained. A new anionic triphenylmethine dye 3,3′-dinitrophenolsulfonephthalein (nitrophenol violet, NPV) was proposed for the study of chemical kinetics. NPV reacts with alkali faster than anionic dyes such as bromophenol blue and phenolphthalein. This property of NPV reduces laboratory practice time.

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