Study Of Acid-base Equilibria Research Articles

THE USE OF TRISTIMULUS COLORIMETRY METHOD APPROACHES IN ACID-BASE EQUILIBRIUM STUDY IN DYES SOLUTIONS (REVIEW)

The present review is concerned with application possibility of tristimulus colorimetry method and argumentation of theoretical basis, and experimental approach of tristimulus colorimetry functions values use as analytical response in studies of acid-base equilibria in solutions of multifunctional organic compounds. A conceptual model is proposed, it is based on the change in tristimulus colorimetry function values in the ionization of functional groups of multifunctional compounds. The definitions of the corresponding terms are described. It has been established that use tristimulus colorimetry functions value as analytical response allows differentiating similar in acid-base characteristics functional groups, to determine the corresponding values of the ionization constants and to build a holistic picture about existing acid-base equilibria in a wide range of acidity of the medium. The values of tristimulus colorimetry functions of the specific and total color difference, the yellowness index, as well as the principles of their calculation within different color spaces by the example of polyfunctional compounds (about 50), namely different classes of dyes (azo-, triphenylmethane, xanthene, anthraquinone and pyrilium derivatives). It is established that all specified functions are suitable for the determination of p Kа , and the use of functions of full color difference makes it possible to simplify the mathematical apparatus for processing experimental data. The advantages of tristimulus colorimetry method before classical instrumental methods (spectrophotometry, potentiometry, conductometry) of studying acid-base equilibria in solutions of polyfunctional compounds are shown.

ACID-BASE EQUILIBRIA IN SOLUTIONS OF NEW 4-HYDROXYSTYRYL DYES BASED ON 1-OCTILPIRIDINIUM

In this paper, the acid-base properties of a number of new 4-hydroxystyryl dyes based on 1-octylpyridinium in solutions have been studied by tristimulus colorimetry and spectrophotometry. The studied dyes are obtained by the interaction of equivalent amounts of corresponding heterocyclic methylene bases salts with 4-hydroxyaldehydes in acetonitrile. The advantages of the tristimulus colorimetric method in the study of acid-base equilibria in dyes solutions were noted. It was shown that the use of data on the change in the values of colorimetric functions (specific color discrimination), depending on the medium acidity allows us to determine the constants of ionization of the functional groups of 4-hydroxystyryl dyes. It was shown that the quantitative description of the color of objects of different nature by calculating their color coordinates on the basis of spectrophotometric data allows obtaining information about their state in solutions. Using the values of the colorimetric functions of the ionic-molecular forms of 4-hydroxystyryl dyes as an analytical signal allows us to obtain a coherent picture of existing acid-base equilibria in a wide range of the medium acidity. Based on the obtained experimental data, a probable scheme of acid-base equilibrium in aqueous solutions of 4-hydroxystyryl dyes was proposed. It was shown that in the acidic medium 4-hydroxystyryl dyes exist in a protonated single-charged cationic form, and with pH rise dissociation of phenolic hydroxyl and tautomerization with the formation of a merocyanine form occurs. The corresponding diagrams for the distribution of ion-molecular forms of 4-hydroxystyryl dyes have been constructed, depending on the acidity of the medium.

Evaluación del equilibrio ácido-base. Aportaciones del método de Stewart

The study of acid-base equilibrium, its regulation and its interpretation have been a source of debate since the beginning of 20th century. Most accepted and commonly used analyses are based on pH, a notion first introduced by Sorensen in 1909, and on the Henderson-Hasselbalch equation (1916). Since then new concepts have been development in order to complete and make easier the understanding of acid-base disorders.In the early 1980's Peter Stewart brought the traditional interpretation of acid-base disturbances into question and proposed a new method. This innovative approach seems more suitable for studying acid-base abnormalities in critically ill patients.The aim of this paper is to update acid-base concepts, methods, limitations and applications.

ChemInform Abstract: Influence of Non-Ionic Polymers on Solvent Properties of Water as Detected by Studies of Acid-Base Equilibria of Sulfonephthalein and Fluorescein Dyes.

ChemInform Abstract: Influence of Non-Ionic Polymers on Solvent Properties of Water as Detected by Studies of Acid-Base Equilibria of Sulfonephthalein and Fluorescein Dyes.

Study of Acid-Base Equilibrium in Chemically Amplified Resist

Protons generated in chemically amplified resists drive pattern formation reactions such as acid catalytic deprotection reactions. Proton dynamics is controlled by the addition of base quenchers so that ultrafine patterns are obtained. However, the details of interaction between protons and base quenchers are still unclear. In this study, we investigated the reactions of protons with base quenchers in a model system of chemically amplified resists with a typical backbone polymer, poly(4-hydroxystyrene). We confirmed that an acid-base equilibrium was reached in the model system without elevating the temperature of the films. The proton affinities of resist ingredients give us a general estimation of protonation sites. When the proton affinities of resist ingredients are close to each other, we have to take into account acid-base equilibrium using pKa for the accurate prediction of protonation sites.

Acid-base equilibria in γ-butyrolactone studied by use of pH-ISFETs

pH-ISFETs were used in the study of acid-base equilibria in γ-butyrolactone (GBL). After the spectrophotometric determination of the p K a value of 3,5-dichloropicric acid, the p K a values and homo-conjugation constants of various acids (including the conjugate acids of bases) were determined potentiometrically using a Ta 2O 5-type pH-ISFET. The values of p K a in GBL were in a linear relation with those in propylene carbonate (PC) and 1.0 units smaller on average. The difference in p K a between GBL and PC was mainly attributable to the difference in proton solvation. The autoprotolysis constant of GBL, roughly estimated by a rapid titration with a Si 3N 4-ISFET, was about 30 on the p K SH scale. A comparative study was made of the response speeds of the Ta 2O 5- and Si 3N 4-type pH-ISFETs and a conventional pH-glass electrode. The result was Si 3N 4-ISFET > Ta 2O 5-ISFET > glass electrode. Because GBL is not stable against acids and bases, the use of pH-ISFETs was much more convenient than the use of the conventional glass electrode.

Spectrophotometric study of acid-base equilibria of 4-(2-benzothiazolylazo)resorcinol and 4-(2-benzothiazolylazo)salicylic acid in water-organic solvent media

The visible absorption spectra of 4-(2-benzothiazolylazo)resorcinol (BTAR) and 4-(2-benzothiazolylazo)salicylic acid (BTAS) have been recorded in water-organic solvent mixtures in the pH range 0.5–12.0. The organic solvents used are methanol, ethanol,n-propanol, iso-propanol, acetone, dioxane and dimethyl formamide. The spectral changes have been explained in terms of shifts in equilibria among different molecular and ionic species of BTAR and BTAS existing in solution. The pKa values corresponding to the different ionization steps have been determined at 25°C and I=0.1M (KNO3) by graphic analysis of the absorbance-pH curves. The results obtained are discussed in terms of the molecular structure of the reagents and the nature of the organic co-solvent used.

Polarographic Study of Acid-base Equilibria of Benzoic Acid and Some Derivatives in Aqueous-alcoholic Solutions

Polarographic Study of Acid-base Equilibria of Benzoic Acid and Some Derivatives in Aqueous-alcoholic Solutions

Liquid Ammonia Solutions VIII. Spectra of Alkali Metal Amide Solutions

Abstract Recently, the spectral characteristics of liquid ammonia solutions containing potassium amide were reported.1 position and intensity of the band associated with these solu- tions is temperature dependent, and it was suggested that the absorption arises from a charge-transfer-to-solvent (ctts) process. Since the amide ion is the strongest base (lyate ion) that can exist in liquid ammonia, its spectral characteristics are especially important in the study of acid-base equilibria involving very weak acids in that solvent; the point of equilibrium in such a system can be moved to a convenient position by the addition of NH2 − (Equation 1). This technique has been used in an analogous situation with cyclohexylamide anion in cyclohexylamine as solvent.2

Buffer Solutions of Potassium Dihydrogen Phosphate and Sodium Succinate at 25 °C.

A buffer mixture consisting of equal molalities (m) of potassium dihydrogen phosphate and sodium succinate is proposed as a useful reference point in the study of acid-base equilibria, bridging the present gap between pH 5.5 and pH 6.8. The p(aHγCl) at 25 °C has been determined by electromotive-force measurements for five buffer solutions in which m varied from 0.005 to 0.025. The conventional paH of each solution has been derived and found to be in good agreement with that calculated from existing data for the two equilibria concerned. The paH varies from 6.251 at m=0.005 to 6.109 at m= 0.025. The buffer mixture has been used successfully for the determination of the dissociation constants of 2-nitro-4-chlorophenol and 2,6-dichlorophenol.