Multiwavelength spectrophotometric determination of acidity constants of 1-(2-thiazolylazo)-2-naphthol in methanol-water mixtures

The acid-base properties of 1-（2-thiazolylazo）-2-naphthol （TAN） in mixtures of methanol-water at 25℃ and an ionic strength of 0.1 mol/L are studied by a multi-wavelength spectrophotometfic method. The acidity constants of all related equilibria are estimated using the whole spectral fitting of the collected data to an established factor analysis model. DATAN program was used for determination of acidity constants. The corresponding pKa values in methanol-water mixtures were determined. There is a linear relationship between acidity constants and the mole fraction of methanol in the solvent mixtures.

Standard potential of the Ag-AgCl electrode and acidity constant of glycine at constant molality of NaCl in glucose-water mixed solvents from 278.15 to 318.15 K

Standard electrode potentials E° of Ag-AgC1 electrode in molality scale and acidity constants of glyeine pK_1° at constant molality of NaCl (1.0 mol·kg^(-1)) in 5 and 15 mass% glucose-water mixed solvents over a range of temperatures from 278.15 to 318.15 K were determined from precise emf measurements.The dependence of acidity constant on temperature is given as a function of the thermodynamic temperature T by an empirical equation, pK_1° =A_1(K/T)-A_2+A_3(T/K).The corresponding thermodynamic quantities of the first dissociation process of glycine were calculated and the effects of both tho solvent and the salt on them were also discussed.

Surface Acidity of Amorphous Aluminum Hydroxide

The surface acidity of synthetic amorphous AI hydroxide was determined by acid/base titration with several complementary methods including solution analyses of the reacted solutions and XRD characterization of the reacted solids. The synthetic specimen was characterized to be the amorphous material showing four broad peaks in XRD pattern. XRD analyses of reacted solids after the titration experiments showed that amorphous AI hydroxide rapidly transformed to crystalline bayerite at the alkaline condition （pH〉10）. The solution analyses after and during the titration Ksp=^aAl^3＋/aH^＋^3 ,was 10^10.3. The amount of consumption of added acid or base during the titration experiment was attributed to both the protonation/deprotonation of dissolved AI species and surface hydroxyl group. The surface acidity constants, surface hydroxyl density and specific surface area were estimated by FITEQL 4.0.

A Potentiometric Evaluation of Stability Constants of Two-Step Overlapping Equilibria via a Bilogarithmic Hyperbolic Cosine Method

A bilogarithmic hyperbolic cosine method for the evaluation of overlapping formation constants at varying (or fixed) ionic strength is devised in this paper and applied to data reported in the analytical literature, i.e. succinic acid system, Cu(II)-glycine system and Ag(I)-aminobutan-1-ol system. The method is based on the linearization of the formation function ? = f(pH) or ? = f(pL) data. A theoretical slope of unity should be obtained thus proving the correctness of the assumed equilibria. An additional advantage of the bilogarithmic method proposed is that it provides a closed scale representation of Y and X unlike other plots. This paper forms part of an investigation into the uses of bilogarithmic methods and hyperbolic functions in parameter estimation. Methods based on the application of spectrophotometric measurements have been the subject of recent studies.

THE DISSOCIATION CONSTANT OF ARACHIDIC ACID BY IR AND LB TECHNIQUES

The dissociation constant of arachidic acid an a subphase containing Ag+ ion was measured by IR and LB techniques.

Effect of Temperature and Solvent Composition on the Acid Dissociation Constants of 2-Pyrrol and 2-Thiophene Aldehyde Phenyl Sulphonyl Hydrazones

Acid dissociation constants, pKa, of 2-pyrrolaldehyde phenylsulphonyl hydrazone, 1, and 2-thiophenealdehyde phenylsulphonyl hydrazone, 2, have been determined spectrophotometrically in ethanol-water media of various compositions over the temperature range 25℃ - 45℃. The obtained results were used in the calculation of the enthalpy, △H°, and the entropy, △S°, of the ionization processes. The slight variations observed in the pKa values of the thiophene compound compared to the pyrrol analogue revealed that neither of the two hetero atoms in the pyrrol or thiophene rings, of the two compounds, is involved in a hydrogen bond chelation. This conclusion was also confirmed through measurements of the dipole moment, IR and NMR spectra.

Theoretical Research on the Multi-channel Reaction Mechanism of CHF Radical with HNCO by Density Functional Theory

The reaction mechanism of CHF radical with HNCO was investigated by the B3LYP method of density functional theory （DFT）, while the geometries and harmonic vibration frequencies of reactants, intermediates, transition states and products were calculated at the B3LYP/6-311＋＋G＊＊ level. In the temperature range of 100-2600 K, the statistical thermody- namics and Eyring transition state theory with Winger correction were used to study the thermodynamic and kinetic characters of the channel with low energy barrier. In addition, the analysis on the combining interaction between CHF radical and HNCO was performed by atom-in-molecules theory （AIM） and natural bond orbitals （NBO） analysis. The calculation results indicated that the reaction of CHF radical with HNCO had ten channels, and the channel of NH direct extraction （CHF ＋ HNCO→IM6→TS7→IM7→CHFNH ＋ CO） in singlet state was the main channel with low potential energy and high equilibrium constant and reaction rate constant. CHFNH and CO were the main products.

Proposal of the partial logarithm of stability constant(PLSC) and its application to rare earth diethylenetriamine-N,N,N',N',N",-pentaacetic acid(DTPA) complexes

The purpose of this article is to propose the idea of ＂a partial stability constant＂ for the complex formation of polyamine polyacetic acids with tripositive rare earth ion. Each coordinating group has its own characteristic stability constant,i.e.,＂the partial stability constant＂ and simple numerical addition can be used among the partial logarithm of the stability constant（PLSC）, for explanation of the total stability constants. The structures of the rare earth-diethylenetriamine-N,N,N＇,N＇,N＂-pentaacetic acid（DTPA）complexes in aqueous solution has been discussed from the point of PLSC.

Determination of the acid dissociation constants of N-carboxymethyl-N-(p-hydroxy phenyl carbamoylmethyl)-2,3-dihydroxy- 5-carbomethoxy benzylamine and the stability constants of its metal complexes

The acid dissociation constants of N-carboxymethyl-N-(p-hydroxy phenyl carbamoyl- methyl)-2,3-dihydroxy-5-carbomethoxy benzylamine(CHDCB) and the stability constants of its 1:1 complexes with alkaline earth, Cd(Ⅱ), Co(Ⅱ), Ni(Ⅱ), Cu(Ⅱ), Zn(Ⅱ), Fe(Ⅲ),Th(Ⅳ)and U(Ⅵ)ions have been determined at 25.0±0.1℃ and at an ionic strength of 0.1(KNO_3)by pH titration method. The probable coordination sites have also been discussed.