In this work an aqueous solution containing a concentration of the dye 5,5',7-indigo trisulfonic acid of 100 mg L-1 have been degraded by an environmentally friendly electrochemical method. Two different supporting electrolytic media, phosphoric acid and sodium sulfate, were used to investigate their contribution in the efficiency of the degradation process. The electrochemical process used is electrochemical peroxidation (ECP), which uses an undivided cell with iron sheets as cathodes and requires the addition of hydrogen peroxide. As a result, the system promotes the production of hydroxyl radicals (.OH) from the Fenton's reaction that takes place between electro generated Fe (II) and the added H2O2. Under optimal conditions a complete color removal is achieved whereas the COD removal is 97%. The sludge generated from the treatment carried out in phosphate media is a fine white powder composed by oxihydroxi Fe-phosphate species. ECP is a highly efficient method for the degradation of the synthetic indigoid dye.

The present work has its basis on the system zirconia-sulfonate in order to study the influence in the variation of the content of the sulfonium ion, carrying out the addition of the agent in situ at a pH=1.8. Results show that solids with a tetragonal type phase, and a distribution of acid sites of the Brönsted and Lewis type with a acid strength of the order of Ho= -14.52 were obtained.

Several efforts have been attempted to study species formation by Nuclear Magnetic Resonance (NMR) in systems with several chemical equilibria present. The majority of these are qualitative and only a few have tried to relate component fractions of a distribution diagram with experimental area fractions determined from NMR spectra to obtain equilibrium constants values. In this work we present a new focus that attempts to relate the species concentration fractions in the system with area fractions beneath NMR peaks to achieve this task. 11B-NMR data of B(III)–H2O systems have been processed with the aid of formation constant values (−log*β) obtained by potentiometry which are 9.17±0.01 for B(OH)3, 9.79±0.08 for B2O(OH)5−, 19.90±0.09 for B3O3(OH)4− and 38.50±0.04 for B5O6(OH)4−, form B(III)–H2O systems with 0.075 M≤[B(III)]total≤0.700 M, in agreement with previous reports and NMR behavior. The treatment of NMR data developed in this work gives a new methodology to obtain formation constants and suggests the possibility to establish a generalization of Beer's law to NMR spectroscopy.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStatistical Study of Distribution Diagrams for Two-Component Systems: Relationships of Means and Variances of the Discrete Variable Distributions with Average Ligand Number and Intrinsic Buffer CapacityRosario Moya-Hernández , Juan Carlos Rueda-Jackson , Josef Havel , María Teresa Ramírez , Guillermo A. Vázquez , and Alberto Rojas-Hernández View Author Information Sección de Química Analítica, Universidad Nacional Autónoma de México, Cuautitlán Izcalli, México; and Departamento de Química, Universidad Autónoma Metropolitana-Iztapalapa, 09340 México, D.F., México Department of Analytic Chemistry, Masaryk University, Brno, Czech Republic Departamento de Química, Universidad Autónoma Metropolitana-Iztapalapa, 09340 México, D.F., MéxicoCite this: J. Chem. Educ. 2002, 79, 3, 389Publication Date (Web):March 1, 2002Publication History Received3 August 2009Published online1 March 2002Published inissue 1 March 2002https://pubs.acs.org/doi/10.1021/ed079p389https://doi.org/10.1021/ed079p389research-articleACS PublicationsRequest reuse permissionsArticle Views200Altmetric-Citations11LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Ligands,Mathematical methods,Phosphates,Teaching and learning methods Get e-Alerts

Predominance zone diagrams have been useful tools in solving problems in analytical chemistry. They can be used to establish the best conditions for separation of mixtures or to optimize recovery procedures for a given species. The few reports on predominance zone diagrams for the participant species in liquid-liquid extraction systems, describe their construction as diagrams of the Pourbaix type (epsilon/pH). With the generalized species and equilibria method (GSEM) it is possible to elaborate Predominance zone diagrams for extraction (PZDE) in proper spaces and with parameters strictly related to these processes such as pH and the volume ratio, r. Therefore, using the GSEM, PZDE that allow us to determine the best conditions for the extraction of a given substance have been elaborated. The stoichiometry of the species been extracted can also be determined from the experimental conditions. It has been demonstrated that with the GSEM, PZDE can be constructed for systems of one and two components. In this work, we intend to demonstrate that the algorithm is valid for the elaboration of PZDE in systems of three and four components. Examples of analytical interest are presented such as lead (II) extraction with diphenyltiocarbazone (dithizone) and that for cadmium (II) with 8-hydroxyquinolein (oxine) in chloroform. The influence of a masking agent, the etilendiaminotetraacetic acid (EDTA) over the extraction of both metals was also assessed.

The hydrolysis of mixed solutions of Al(III), Ga(III), Al(III), Ln(III) and Zr(IV) was studied by potentiometric, spectrophotometric and 27Al- and 71Ga-NMR techniques. For the Al–Ga system formation of GaAl12(OH)11+28 species seems more probable into the pH range 4≤pH≤5. Afterwards, the Al13(OH)7+32 species predominate in agreement with thermodynamic data obtained by SUPERQUAD program. Both tetrahedral GaIV and AlIV may coexist in solution, the interval being defined by potentiometric methods. For the Ln(III)–Al(III) systems 27Al-and 139La-NMR does not confirm the chemical interaction between the two species in solution, but the physicochemical properties of the La–Al/PILCS were different than Al/PILCS, suggesting a strong interaction in the solid state. Ce(III) and Ce(IV) ions do interact with Al(III) in solution, into the pH range 2.783.0.

Formation constants for recrystallized thymol blue were determined in water, using the SQUAD and SUPERQUAD programs. The best model correlating spectrophotometric, potentiometric and conductimetric data was fitted with the dissociation of HL−=L2−+H+−log K=8.918±0.070 and H3L2−=2L2−+3H+−log K=29.806±0.133 with the SUPERQUAD program at variable low ionic strength (1.5×10−4–3.0×10−4 M); and HL=L2−+H+−log K=8.9±0.000, H3L2− =2L2−+3H+−log K=30.730±0.032, H4L2=2L2−+4H+−log K=32.106±0.033 with SQUAD at 1.1 M ionic strength.

The voltammetric characterization of ferrocene confined within a carbon paste electrode (CPE) with nonconducting binder (Nujol or silicon oil) was performed. The voltammetric behavior depends directly on the way in which the electroactive species were introduced into the paste: as a solid or previously dissolved into the binder. These two forms were found to contribute in the electrochemical process in a single voltammetric peak. Variations in the potential sweep rate, type of binder (meaning changes in ferrocene solubility), the amount of binder in the paste, and also the amount of the electroactive species affect the shape of the voltammetric curves obtained. This enables us to distinguish between the contributions of the solid and dissolved forms of ferrocene in the voltammetric response. From this study, it is established that the ferrocene oxidation in CPE was limited by diffusion, taking place in a layer beyond the electrode-electrolyte interface, resulting from the dissolution of ferrocene within the binder. The existing controversy reported for voltammetric studies of ferrocene in CPE could be explained by the presence of two different ferrocene species involved in the oxidation process.

The application of SQUAD to the refinement of formal potentials from potentiometric or coulometric steady-state and spectrophotometric measurements was tested. The formal potential thus obtained for the Fe(CN) (3-)(6)Fe(CN) (4-)(6) couple in 0.5 M H(2)SO(4) agreed with published data. This method was found to be satisfactory for the determination of typical standard potentials and it is suggested that it may be advantageous when dealing with multi-component systems.

Diphenylcarbazide (DPCI) or diphenylcarbazone (DPCO) is introduced into carbon paste electrodes in order to determine the potential ranges where the oxidation-reduction processes of these species occur in 0.3 M HClO4. The potential controlled electrolysis was performed for DPCI and DPCO dissolved in 0.3 M HClO4. From the coulometric results and the UV-visible spectral data of the solution before and after the electrolysis it is possible to establish that DPCI is oxidized in an irreversible process giving diphenylcarbadiazone (DPCDO). DPCO is probably an intermediate in this oxidation, but its concentration is never high because it is slightly more easily oxidized than DPCI. DPCO can be reduced to DPCI at about 0.2 V (ECS) and, finally, DPCDO can be reduced to DPCI at about −0.5 V (ECS). Again, DPCO is probably an intermediate but is not detected because it is so much more easily reduced than DPCDO.

The early stages of the electrolytic deposition of silver onto vitreous carbon electrodes from ammonium hydroxide solutions have been investigated by the potential step technique. The analysis of the experimental current transients according to existing theories indicates that this process occurs by multiple three-dimensional nucleation, followed by diffusion controlled growth of nuclei. It is shown that treatments that involve classifying the process as either instantaneous or progressive nucleation are not always adequate for the quantitative analysis of electrochemical nucleation phenomena. The nucleation kinetics parameters A (nucleation rate constant per site) and No (number density of active sites on the substrate surface) were estimated separately from the current transient maxima by two different approaches. Both quantities were found to vary with the potential and with the concentration of silver ions, except at very high overpotentials for silver deposition. The potential dependence of the nucleation rate A was interpreted according to the atomistic theory and in all cases it was found that the number of atoms in the critical nucleus (n(k)) was one over the entire potential range analyzed.

A method for the construction of carbon paste electrodes (CPE) is described. Here ferrocene is used as the insoluble electroactive species, graphite powder as conductor and sulfuric acid as binder. The CPE thus prepared prevents ferrocenium ions from diffusing towards the bulk solutions. Voltammetric, chronopotentiometric and chronoamperometric experiments performed with these CPEs show that the different preparation methods yield different electrochemical parameters for the ferrocene-ferrocenium system.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPredominance-Zone Diagrams in Solution Chemistry: Dismutation Processes in Two-Component Systems (M-L)A. Rojas-Hernández , M. T. Ramírez , I. González , and J. G. Ibáñez View Author Information Universidad Autonoma Metropolitana-Iztapalapa, Departmento de Quimica, Apartado Postal 55-534, 09340 Mexico, D. F. MexicoCite this: J. Chem. Educ. 1995, 72, 12, 1099Publication Date (Print):December 1, 1995Publication History Received3 August 2009Published online1 December 1995Published inissue 1 December 1995https://pubs.acs.org/doi/10.1021/ed072p1099https://doi.org/10.1021/ed072p1099research-articleACS PublicationsRequest reuse permissionsArticle Views329Altmetric-Citations25LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

In this second part a general algorithm is presented which is based on the definition of total generalized species and equilibria and the combination of Charlot and Ringbom's approaches; this leads to the establishment of the relative importance of the chemical species present in a multi-component-multi-reacting system that includes complexation, polynucleation and phase-formation phenomena. The definition of total generalized species [†M(τ) and †M(τ(c)] permits as expression to be obtained for the total generalized intrinsic solubility equilibria for the calculation of the saturation conditions in a solution in spite of the presence of polynuclear species both in the solution and in the condensed phases. The symbol used for the total generalized species implies that the subscripts for the polynucleation of M are included in the superscript dagger (†). The procedure used to select the most insoluble phase from the condensed-phases diagram of this system was described in Part I. In order to exemplify the scope of the proposed algorithm, graphical representations of the following systems are discussed: Be(II)H2OH, Be(II)H4PDTAH2OH, (Ca(II)H3PO4H2OH and Mg(II)H3PO4NH3H2OH, where H4PDTA is 1,3-diaminopropylene-N,N,N′,N′-tetraacetic acid.

In this second part a general algorithm is presented which is based on the definition of total generalized species and equilibria and the combination of Charlot and Ringbom's approaches; this leads to the establishment of the relative importance of the chemical species present in a multi-component-multi-reacting system that includes complexation, polynucleation and phase-formation phenomena. The definition of total generalized species [(dagger)M(tau)) and (dagger)M(c)(tau)] permits an expression to be obtained for the total generalized intrinsic solubility equilibria for the calculation of the saturation conditions in a solution in spite of the presence of polynuclear species both in the solution and in the condensed phases. The symbol used for the total generalized species implies that the subscripts for the polynucleation of M are included in the superscript dagger (dagger). The procedure used to select the most insoluble phase from the condensed-phases diagram of this system was described in Part I. In order to exemplify the scope of the proposed algorithm, graphical representations of the following systems are discussed: Be(II)-H2O-H, Be(II)-H4PDTA-H2O-H, Ca(II)-H3PO4-H2O-H and Mg(II)-H3PO4-NH3-H2O-H, where, H4PDTA is 1,3-diaminopropylene-N,N,N',N'-tetraacetic acid.

A definition of generalized species and equilibria (including the concepts of ampholyte and disproportionation or dismutation) is proposed for the study of polynucleation phenomena in systems with multiple buffering and mixed complexes. With this method, it is possible to draw multi-dimensional predominance-zone diagrams (PZD) for such systems. Three alternative methods for the graphical representation of the PZD are discussed, which use the parameters pM, −log C and −log Cmtotal; the relationship among them is shown and also the fact that multi-conditional dismutation constants are the only criteria for the intrinsic stability of ampholytes. In order to exemplify the proposed method, a study of the systems Be(II)-H and Be(II)-PDTA-H is reported (where PDTA=species of 3-propylenediamino-N,N,N′,N′-tetraacetic acid, which is represented by H4PDTA).

A generalized method for the construction of predominance-zone diagrams using conditional constants is presented. This generalization permits the construction of multidimensional diagrams using multiconditional constants for the study of chemical equilibria in aqueous solutions of multicomponent systems. The predominance-zone diagrams can be constructed by defining generalized species, complexation coefficients (with a multiplicative structure instead of the traditionally used additive structure) and generalized complexation and dismutation equilibria for multibuffered systems. Systems involving mixed complex formation were studied by using copper(II)-nitrilotriacetic acid-histidine-proton (under buffered conditions in pHist′ and pH) and mercury(II)-ethylenediaminetetraacetic acid-ammonia-proton (under buffered conditions in pNH3′ and pH) as examples.

A method for the construction of predominance-zone diagrams of multicomponent and multiphase systems of chemical species in a single oxidation state, which consider the formation of mixed and polynuclear complexes (of the type M(i)L(j)X(k)) is presented. Such diagrams may be constructed by defining generalized species, complexation coefficients (with multiplicative structure) and generalized equilibria of complexation, dismutation, polynucleation, and phase formation, with their conditional constants associated. By having these diagrams for each oxidation state of the same component, multidimensional Pourbaix diagrams are constructed. The predominance-zone diagrams of *Eu(0), *Eu(II), and *Eu(III) in the presence of citric acid (H-3Cit) and nitrilotriacetic acid (H-3NTA) in aqueous solution, are constructed by using this approach.