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Journal
2010 | 8 | 2 | 392-395
Article title

Spectrophotometric determination of aqueous acidity constants of three azo dyes

Content
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EN
Abstracts
EN
The two successive steps acidity constants of three azo dye derivatives D1–D3, were determined by a spectrophotometric method using 0.10 M KNO3 as supporting electrolyte in water solvent. The electronic spectra of the compounds were recorded in the course of their pH-metric titration with a standard base solution. The protolytic equilibrium constants can be solved very satisfactorily from absorbance data, by combining the data obtained in the spectrometric determinations with graphic methods as the absorbance diagrams. An A-diagram shows the relative absorbance changes at two wavelengths as a function of the pH. For a one-step system, the absorbance at any wavelength must be proportional to the absorbance at any other wavelength, so an A-diagram for all wavelength combinations for such a system must be linear (rank, s=1). However, if a system is governed by two or more equilibria, the A-diagrams corresponding to multi-step titrations will change direction every time a new equilibrium becomes dominant in the system. Analysis of the each uniform sub-region can then be used in evaluating of the corresponding equilibrium. A-diagrams for all wavelength combinations suggest that these systems have the rank two(s=2). The results revealed that the Ka(1) and Ka(2) values of different azo dyes follow the order D3>D2>D1. [...]
Publisher
Journal
Year
Volume
8
Issue
2
Pages
392-395
Physical description
Dates
published
1 - 4 - 2010
online
23 - 3 - 2010
References
  • [1] J. Havel, M. Meloun, Computation Methods for the Determination of Formation Constants (Plenum Press, New York, 1985)
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  • [5] J. Polster, H. Lachmann, Analysis of Chemical Equilibria (VCH, Weinheim, 1989)
  • [6] K. Haghbeen, E. Tan, J. Org. Chem. 63, 4503 (1998) http://dx.doi.org/10.1021/jo972151z[Crossref]
Document Type
Publication order reference
YADDA identifier
bwmeta1.element.-psjd-doi-10_2478_s11532-010-0001-7
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