Gravimetric determination of silver as silver chromate

Summary Gravimetric estimation of silver, based upon its quantitative precipitation as normal silver chromate, Ag₂CrO₄, is described.     

Electrochemical reduction mechanism of silver chromate in lithium cells

A general mechanism is proposed to explain the charge—discharge features of the LiAg₂CrO₄ system.For a low discharge rate, the process leads to Ag and Li₂CrO₄ formation through a dissolution—precipitation, mechanism. Li₂ CrO₄ is reducible in two steps at lower potentials. For high discharge we show the formation of an intermediate compound, called Ag ₂, Li₂CrO₄ which evolves either to a mixture of metallic Ag and Li₂CrO₄ or is reduced with the formation of a Cr(V) compound at higher potential than Li₂CrO₄.This mechanism obtained with experimental electrodes is in excellent agreement with the behaviour of Ag₂CrO₄ commercial cells.     

Periodic precipitation of silver chromate/dichromate in gelatin

The spatial and temporal evolution of silver chromate/dichromate Liesegang Rings (LR) in gelatin is studied microdensitometrically and microscopically. The analysis of the distribution of various ionic species in dichromate solutions leads to a notion of the possibility of both silver chromate and silver dichromate precipitation. A simple mathematical model of diffusion in thin layers has been developed. The results of the turbidity front progression measurements are consistent with this model and, together with the secondary structure observations, support the postnucleation hypothesis of primary LR formation.     

Conditions of the formation of yellow sol of silver chromate

Yellow sol of silver chromate is obtained in gelatin medium when the reactants are either dilute or when the amount of silver nitrate is lesser than the equivalent amounts. In agar agar and aqueous medium, yellow sol is obtained in the presence of sodium citrate. This yellow sol is suddenly converted into a red suspension after a certain period. The time of conversion of yellow sol to red suspension increases as the reactants are diluted or concentration of sodium citrate is increased or when the amount of silver nitrate added is reduced. In presence of sodium citrate and smaller concentrations of AgNO₃, a stable yellow sol could be obtained in aqueous medium.

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Zusammenfassung Gelbes Silberchromatsol wird in Gelatine erhalten, wenn die reagierenden Komponenten entweder verdünnt sind oder wenn der Betrag an Silbernitrat geringer als äquimolekular ist. In Agar-Agar und Wasser wird gelbes Sol in Gegenwart von Natriumzitrat erhalten. Dieses gelbe Sol wandelt sich plötzlich nach einer gewissen Zeit in eine rote Suspension um. Diese Zeit wächst, wenn die Reagenzien sehr verdünnt sind oder die Konzentration des Natriumzitrats gesteigert wird oder der Anteil an zugefügtem Silbernitrat verringert wird. In Gegenwart von Natriumzitrat und kleinen Konzentrationen von Silbernitrat konnte in Wasser ein stabiles gelbes Sol erhalten werden.

     

Behaviour of silver—silver malonate and silver—silver succinate electrodes in aqueous media

The silver—silver oxalate electrode has been employed by many workers^1–3 in aqueous media as the second order reference electrode, but no work seems to have been done so far on the study of the behaviour of silver—silver malonate and silver—silver succinate electrodes. The present work deals with the study of these electrodes in ionic equilibria of malonate and succinate ions in aqueous media. These electrodes, in conjunction with a saturated calomel electrode, have been employed in the poten- tiometric determination of malonate and succinate ions in aqueous media. In additon, the effect of the added salts, such as, potassium nitrate and sucrose on the behaviour of these electrodes has also been examined in this media.     

Spectral studies on silver chromate and nitrate complexes with heterocyclic amines

Silver chromate and nitrate complexes of the general formulae [Ag₂(L)_x(CrO₄)] and [Ag(L)_x(NO₃)] (L—heterocyclic amine) were synthesized and spectrally investigated. The coordination of the anion in [Ag₂(4,′4bipy)(CrO₄)] and [Ag₂(HMTA)(CrO₄)] was proposed from the IR data. A prominent matrix effect on the electronic spectra has been observed.     

Condition of copper chromate in the medium of lyophilic sols by conductometric measurements

Summary The condition of copper chromate in different lyophilic sols has been studied by conductometric measurements. There is no evidence of the formation of supersaturated solution of this salt in either of the lyophilic sols.

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Zusammenfassung Das Verhalten von Kupferchromat in verschiedenen lyophilen Solen wurde konduktometrisch untersucht. Es gibt keine Wahrscheinlichkeit dafür, da? sich übers?ttigte L?sungen dieses Salzes in irgendeinem der lyophilen Sole bilden.

     

Behaviour of glass and silver/silver chloride electrodes in some non-aqueous media

The stability of glass electrodes and silver/silver chloride electrodes in isopropanol, methyl ethyl ketone and a mixture of equal volumes of these has been measured, and found to be of the order of 1 mV. Changes in the electrode potential due to addition of water and to addition of supporting electrolyte have been investigated. The glass electrode responded reversibly to hydrogen ion activity changes in buffers of picric acid-tetraethylammonium picrate, and perchloric acid-di-isopropylamine. The autoprotolysis constants at 25 degrees were calculated to be 2 x 10(-19) in isopropanol, 2 x 10(-26) in the ketone and 8 x 10(-19) in the mixture.     

Solubility studies in aqueous media: I. Solubility product of silver permanganate and standard electrode potentials of silver—silver permanganate electrode in aqueous media

The solubility and solubility product of silver permanganate in water have been determined at the temperatures ranging from 15 to 35°C over 5°C intervals in the presence of an added electrolyte, sodium perchlorate. The solubility of silver permanganate ranges from 0.966 x 10^?5 mol 1^?1 at 15°C to 1.420x10^?5 moll^?1 at 35°C and the corresponding solubility product 0.933 x 10^?10 mol² 1^?2 at 15°C to 2.017 x 10^?10 mol² 1^?2 at 35°C. The standard potentials of the Ag(s)/AgMnO₄(s)/ MnO^?₄ electrode have been calculated at these temperatures. The mean activity coefficients of silver permanganate at various rounded molarities of sodium perchlorate solutions, and the standard thermodynamic quantities for the process AgMnO₄(s)→Ag⁺ (aq)+MnO^?₄(aq) have been calculated at these temperatures.     

Generation of silver and lead chromate nanoparticles in Triton N-42 and AOT reversed-micellar solutions

A process is proposed for manufacturing silver and lead nanoparticles in Triton N-42 and AOT solutions in decane. The completion of nanoparticle formation and solution stability were studied spectrophotometrically as functions of the parameters of reversed-micellar systems (the nature and proportion of the surfactant, solubilization capacity, reagent concentrations, and their ratios). Atomic absorption spectroscopy (AAS) and X-ray powder diffraction (XRD) showed that the nanoparticles isolated from Triton N-42 and AOT solutions compositionally correspond to and are isostructural to Ag₂CrO₄ and PbCrO₄. Mean nanoparticle sizes are 15–30 nm as determined by transmission electron microscopy (TEM).     

Fluorescence of pyrene in inhomogeneous media containing silver nanoparticles

Pyrene fluorescence in inhomogeneous media based on ionic detergents containing silver nanoparticles with different morphologies is investigated. An increase in pyrene monomer emissions in the spectral range of 400–500 nm is observed, due to the resonance between electronic transitions in pyrene molecules in that region and the plasmonic oscillations of silver nanoparticles.     

Effect of the rate of diffusion of ions on the periodic precipitation of silver chromate

The effect of the rate of diffusion on the formation ofLiesegang rings of silver chromate in gelatin and agar agar medium has been studied. The rate of diffusion of silver ions in the agar agar gel is much slower than that in gelatin gel during the formation of rings of silver chromate. If the rate of diffusion of silver ions in agar agar gel is increased, even then rings do not form. The only change brought about by the rate of diffusion is for the distance between the successive rings.

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Zusammenfassung Der Einflu\ der Diffusionsgeschwindigkeit auf die Bildung vonLiesegang-Ringen aus Silberchromat in Gelatine und Agar-Agar wurde untersucht. Die Diffusionsgeschwindigkeit der Silberionen in den Agar-Agar-Gelen ist viel niedriger als in den Gelatinegelen während der Bildung der Ringe von Silberchromat. Wenn die Diffusionsgeschwindigkeit der Silberionen in Agar-Agar-Gelen gesteigert wird, bilden sich schlie\lich überhaupt keine Ringe. Der einzige Einflu\, den die Diffusionsgeschwindigkeit hervorruft, ist also änderung des Abstandes aufeinanderfolgender Ringe.

     

Electrochemical formation and reduction of silver oxides in alkaline media

The anodic oxidation of silver electrodes in NaOH solution and the reduction of the silver oxides formed were studied by potential step chronoamperometry. Oxidation of Ag to Ag₂O is a diffusion-controlled reaction, the diffusion control being established in the solid phase. Oxidation of Ag₂O to AgO proceeds via a nucleation and growth-controlled process. The amount of AgO decreased with increasing step height. The current—time curves for this reaction have been analysed with the Kolmogoroff—Avrami equation. Reduction of AgO to Ag₂O occurs initially on the outside of the electrode, and the rate of the reaction is limited by diffusion of ions across the thickening layer of Ag₂O. Reduction of Ag₂O to Ag proceeds via a nucleation and growth reaction.     

Potentiometric study of silver complexes with thiourea in acid media

Formation of silver complexes with thiourea in three different acids (perchloric, methanesulfonic, and sulfamic) was studied potentiometrically using modified Leden's method. It was established that, under conditions similar to the ones used for commercial electroplating of silver alloys, silver and thiourea form predominantly binuclear complexes Ag₂tu _n (n =?1–6). Calculated complex stability constants were similar in all cases suggesting that the acidity and the type of anion have little effect on the structure.     

Laser-induced changes in silver metal nanoparticles incorporated in viscous media

The effect of laser pulse irradiation on silver metal nanoparticles in ethylene glycol and glycerol is studied and compared with the parallel processes in aqueous solutions. The influence of 355 nm laser pulse irradiation at the surface plasmon frequency and on the size of the silver nanoparticles is examined by UV-Vis absorption spectroscopy and by transmission electron microscopy. It appears that viscosity of the medium plays a crucial role for the stabilization of the melted particles in the absence of the stabilizer. In ethylene glycol containing PVP, fragmentation of particles was observed. In neat glycerol, similar excitation led to morphological changes as the nanoparticles fused to produce particles of larger size. The changes in reduction of shape and size are considered to occur through melting and vaporization of the silver nanoparticles.     

Reaction between silver trifluoroacetate and quercetin in low-polarity organic media

CF₃COOAg-Qr-P systems, where Qr is quercetin and P is an organic solvent, have been studied by spectroscopic methods. The reaction between silver trifluoroacetate and quercetin has been shown to produce colloid solutions, whose destruction terminates with the precipitation of a silver phase. The kinetic characteristics of the reaction between silver trifluoroacetate and quercetin in ethyl acetate have been determined.     

Formation of surface layers on silver nanoparticles in aqueous and water-organic media

Synthetic aspects of silver nanoparticle preparation in one-and two-phase aqueous and water-organic media and the influence of experimental factors on particle size and surface hydrophilicity/hydrophobicity are studied. It is shown that silver nanoparticles with controlled mean size and surface hydrophilic-hydrophobic properties can be obtained through direct synthesis or successive transformations.     

Surfactant-assisted synthesis and characterization of stable silver bromide nanoparticles in aqueous media

Colloidal dispersions of silver bromide (AgBr) in aqueous surfactant medium have been prepared using a surfactant-assisted synthesis approach with hexadecyltrimethylammonium bromide (CTAB). The surfactant acts both as source of bromide ion as well as the stabilizing agent. Upon progressive addition of silver nitrate to aqueous CTAB solution, stable AgBr dispersions were obtained. Formation of surfactant cation (CTA(+)) stabilized AgBr was confirmed by way of XRD, FTIR and NMR studies. Thermal behavior of the isolated nanoparticles was investigated by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA), where the occurrence of phase transition in the surfactant-stabilized nanoparticles was observed. Kinetics of the particle growth was investigated by dynamic light scattering measurements, which predicted the formation of surfactant bilayered structures associated with the nanoparticles of AgBr. Band gap of the nanoparticles was determined by suitably analyzing the UV-visible spectral data, which concluded that the particles behaved like insulators. Morphology of the particles, studied by TEM measurements, was found to be spherical. Finally, enthalpy of formation of surfactant-stabilized AgBr, determined calorimetrically, was found to be dependent on the concentration of the precursors.