Acid–base behaviour of the ferrocyanide ion in perchloric acid media potentiometric and spectrophotometric study

1987 ◽  
Vol 65 (3) ◽  
pp. 583-589 ◽  
Author(s):  
Pedro L. Domingo ◽  
Begoña Garcia ◽  
Jose M. Leal
Keyword(s):  
Perchloric Acid ◽  
Spectrophotometric Study ◽  
Separate Study ◽  
Acid Base ◽  
Acid Media ◽  
Protonation Equilibria ◽  
The Third ◽  
Brønsted Base

Ferrocyanide ion behaves as a tetravalent Brønsted base and can react with four protons, forming ferrocyanic acid. By potentiometric and spectrophotometric techniques it is shown that the first two protonation equilibria overlap, as do the third and fourth equilibria. The two techniques yield identical results when processed with the inclusion of non-ideality terms. The method of "separation of equilibria" is proposed to allow separate study of each of the overlapping equilibria. Values of pK1 = −2.54 ± 0.10, pK2 = −1.08 ± 0.03, pK3 = 2.65 ± 0.02, and pK4 = 4.19 ± 0.02 were obtained.

Acid–base behaviour of the ferricyanide ion in perchloric acid media. Spectrophotometric and kinetic study

1990 ◽  
Vol 68 (2) ◽  
pp. 228-235 ◽  
Author(s):  
Pedro L. Domingo ◽  
Begoña García ◽  
José M. Leal
Keyword(s):  
Kinetic Study ◽  
Perchloric Acid ◽  
Decomposition Reaction ◽  
Acid Base ◽  
Acid Media ◽  
Protonation Equilibria ◽  
Aqueous Perchloric Acid ◽  
Protonated Species ◽  
Heterolytic Dissociation ◽  
Homolytic Dissociation

A wide study was carried out of the acid–base behaviour of ferricyanide ions in aqueous perchloric acid media in the range 0.1–11.5 M. This study shows that protonation and decomposition of the ferricyanide ions occur simultaneously. The three successive protonation equilibria were found in the acidity ranges 0.1–4.0, 3.5–8.5, and 7.0–11.5 M HClO4, respectively. A kinetic study was also made of the decomposition reaction at 60 °C. The kinetic data are explained by considering a reaction mechanism involving homolytic and heterolytic dissociation steps. The homolytic and heterolytic rate constants corresponding to each of the four protonated species were determined, along with the acid–base protonation constants, pK1 = −6.25 ± 0.10; pK2 = −3.23 ± 0.03; and pK3 = −0.60 ± 0.02. Keywords: acid–base behaviour, protonated species, decomposition, homolytic dissociation, heterolytic dissociation.

The pKBH+ calculation of strong bases: A revision of various methods

1987 ◽  
Vol 52 (2) ◽  
pp. 299-307 ◽  
Author(s):  
Begoña García ◽  
José M. Leal
Keyword(s):  
Perchloric Acid ◽  
Infinite Dilution ◽  
Polynomial Function ◽  
Acid Base ◽  
Third Order ◽  
Acid Media ◽  
The Third ◽  
Aniline Derivatives ◽  
New Methods

The pKBH+ values have been obtained for seventeen acid-base equilibriums corresponding to thirteen aniline derivatives in dilute perchloric acid media in the pH region at 25 °C using the spectrophotometric technique. By revising the method of extrapolation to infinite dilution it was possible to introduce new methods for calculating pKBH+ values of strong bases by means of the functions logI = f(pH) and pKap = f(pH). The equation - logfBH+/fB = f(pH) - has been proved to conform to a polynomial function of the third order and is applicable to each compound.

Spectrophotometric study of the acid-base and optical properties of the 5-bromo and 5-chloro derivatives of 2-(2-pyridylazo)-5-(diethylamino)phenol (BrPADAP, ClPADAP) and their complexation equilibria with zinc(II) ions

1982 ◽  
Vol 47 (10) ◽  
pp. 2676-2691 ◽  
Author(s):  
Miroslav Macka ◽  
Vlastimil Kubáň
Keyword(s):  
Equilibrium Constants ◽  
Spectrophotometric Study ◽  
Graphical Analysis ◽  
Alkaline Media ◽  
Acid Base ◽  
Ethanol Medium ◽  
Triton X ◽  
Mixed Water ◽  
Derivatives Of

The optical and acid-base characteristics of BrPADAP and ClPADAP were studied in mixed water-ethanol and water-DMF media and in 10% ethanol medium in the presence of cationic, anionic and nonionic tensides. The composition, optical characteristics, molar absorption coefficients and equilibrium constants of the ML and ML2 complexes with zinc(II) ions were found by graphical analysis and numerical interpretation of the absorbance curves by the modified SQUAD-G program. Optimal conditions were found for the spectrophotometric determination of Zn(II) in the presence of 0.1% Triton X-100 or 1% Brij 35 in alkaline media with pH = 6.5-10. BrPADAP and ClPADAP are the most sensitive reagents (ε = 1.3-1.6 . 105 mmol-1 cm2 at 557 and 560 nm, respectively) for the determination of zinc with high colour contrast of the reaction (Δλ = 104 nm) and selectivity similar to that for the other N-heterocyclic azodyes (PAN, PAR, etc.).

Spectrophotometric study of the interaction of Chromazurol S and Eriochromazurol B with surface active substances - tensides

1981 ◽  
Vol 46 (5) ◽  
pp. 1090-1106 ◽  
Author(s):  
Irena Burešová ◽  
Vlastimil Kubáň ◽  
Lumír Sommer
Keyword(s):  
Critical Micellar Concentration ◽  
Spectrophotometric Study ◽  
Conditional Stability ◽  
Acid Base ◽  
Binary Complexes ◽  
Chromazurol S ◽  
Acid Base Equilibrium ◽  
Poorly Soluble ◽  
Conditional Stability Constants ◽  
Triton X

The acid-base and optical properties of Chromazurol S and Eriochromazurol B in the presence of 1 . 10-6 - 2 . 10-2M solutions of cetylpyridinium bromide, cetyltrimethylammonium bromide and 1-ethoxycarbonylpentadecyltrimethylammonium bromide (Septonex) and 0.001-1.0% w/v solutions of octylphenolpolyethylene glycol ether (Triton X-100), polyoxyethylenemonolauryl ether (Brij 35) and lauryl sulphate sodium salt were determined by graphical and numerical interpretation of absorbance curves. The poorly soluble ion associates, which can be extracted into chloroform and which have the defined composition [LH4-nn-.n T+] or [LH3-nn-.n T+] are formed at submicellar concentration of the tenside. In regions close to the critical micellar concentration of the tenside, soluble binary complexes of the acid-base forms of the reagent are formed with tenside micelles. The conditional stability constants of the reagent acid-base equilibrium depend on the type and concentration of the tenside, on the reagent concentration, on the concentration and type of inorganic acid anions and on the ionic strength of the solution. The mechanism of interaction of the reagent with the tenside and the probable structure of the binary species are discussed.

Spectrophotometric study of the effect of sodium dodecyl sulphate on the acid-base behaviour of 4-(2-pyridylazo)-resorcinol

1991 ◽  
Vol 56 (4) ◽  
pp. 785-795 ◽  
Author(s):  
Jiří Bílý ◽  
Ludmila Čermáková ◽  
Jiří Knapp
Keyword(s):  
Surface Tension ◽  
Critical Micelle Concentration ◽  
Sodium Dodecyl Sulphate ◽  
Azo Dye ◽  
Dissociation Constants ◽  
Sodium Dodecyl ◽  
Spectrophotometric Study ◽  
Acid Base ◽  
Strong Electrolytes ◽  
The Given

The values of the apparent dissociation constants of the azo dye 4-(2-pyridylazo)-resorcinol (PAR) have been found in the presence of sub- and supercritical concentrations of the anionogenic tenside sodium dodecyl sulphate (SDS) and the effects of the strong electrolytes NaCl and NaNO3 were also evaluated. In both electrolytes, the pKan values initially are independent of the SDS concentration and then increase. Spectrophotometric and surface tension measurements were employed to determine the critical micelle concentration (cmc) of SDS alone and in the presence of PAR and the given electrolytes. The determined cmc values were in the range 0.20–3.02 mmol l-1 and dependent on the type and concentration of the particular additive.

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