Silver anion adsorption

Horanyi G and Rizmayer E M 1984 Radiotracer study of anion adsorption at silver electrodes in acidic medium J. Electroanal. Chem. 176 339-48... 

Discussion. The method is applicable to the determination of a mixture of two salts having the same anion (e.g. sodium chloride and potassium chloride) or the same cation (e.g. potassium chloride and potassium bromide). For example, to determine the amount of sodium and potassium chlorides in a mixture of the two salts, a known weight (Wj g) of the solid mixture is taken, and the total chloride is determined with standard 0.1 M silver nitrate, using Mohr s method or an adsorption indicator. Let w2 g of silver nitrate be required for the complete precipitation of Wj g of the mixture, which contains xg of NaCl and yg of KC1. Then ... 

Delgado JM, Orts JM, Rodes A. 2005. ATR-SEIRAS study of the adsorption of acetate anions at chemically deposited silver thin film electrodes. Langmuir 21 8809-8816. 

In general, the contact adsorption of deh3drated anions changes the interfacial lattice structure of adsorbed water molecules, thereby changing the interfadal property. For example, the clean surfaces of metallic gold and silver, which are hydrophobic, become hydrophilic with the contact adsorption of dehydrated halogen anions. 

Gold is one of the least reactive metals in bulk form. However, in recent years a considerable amount of theoretical and experimental works have studied the reactivity of small neutral and charged Au clusters towards different molecules, like H2, O2, CO, and organic radicals " . The reactivity depends on the size and charge state of the cluster. In the previous section we have studied the reactivity towards oxygen adsorption of anionic silver and gold clusters. In this section we study the reactivity of neutral gold clusters towards molecular O2 (subsection 6.1) and CO (subsection 6.2). 

The electrosorption valency usually increases as the underpotential decreases to approach the ionic charge (total discharge of the cation) close to the Nernst potential, for instance in the case of lead and thallium upd on silver [114]. However, the co-adsorption of anions may contribute to the observed apparent electrosorption valence, as rotating ring disc electrode (RDE) experiments have shown [113]. 

The area determinations by dye adsorption from solution discussed here are applicable to aqueous dispersions. Although saturation coverage of silver halides by Pseudocyanine remained unchanged in 40% methanol by volume, it is known that in organic solvents where ion-pairs may be adsorbed, the molecular cross section of the cyanine can vary with the dye s anion—cf. Reference 23 for discussion and literature citations. Recent determinations of Agl areas by adsorption of Pseudocyanine were reported to have been unrealistic and salt-dependent (van den Hul, H. J., Lyklema, J., J. Phys. Chem. 90, 3010 (1968)). A likely reason for this result is the circumstance that these investigators carried out their measurements in alcohol dispersions of the substrate where the cited solvent-dependent limitations would apply. 

Anions bind also to other metals, like gold, platinum, or silver [74,81], Why do anions adsorb specifically to metals, while cations do not The explanation is a strong hydration of cations. A cation would have to give up its hydration shell for an adsorption. This is energetically disadvantageous. Anions are barely hydrated and can therefore bind more easily to metals [82], Another possible explanation is the stronger van der Waals force between anions and metals. The binding of ions to metallic surfaces is not yet understood and even the idea that cations are not directly bound to the metal, was questioned based on molecular-dynamics simulations [83],... 

Another class of indicators, known as adsorption indicators, adsorb to (or desorb from) the precipitate or colloidal particles of the silver salt of the analyte at the equivalence point. The indicator anions are attracted into the counterion layer surrounding each colloidal particle of silver salt. Thus, there is a transfer of color from the solution to the solid or from the solid to the solution at the end point. The concentration of the indicator, which is an organic compound, is not large enough to cause its precipitation as a silver salt. Thus, the color change is an adsorption and not a precipitation process. Fluorescein is a typical example of an adsorption indicator in argentometric titration. 

Due to the fact that the membranes are formed from sparingly soluble salts, adsorption or desorption on the surface can be of cation or anion, the electrode being sensitive to both species. It is also sensitive to any other ion that forms a sparingly soluble precipitate on the membrane surface. For example, the silver sulphide electrode responds to Hg2+. 

It has been shown that Cu and Ag dissolve at essentially the same transport-controlled rate in acidified ceric sulfate solution (37). The authors postulate that the larger enthalpy of this reaction facilitates desorption of the product ions. The equilibrium adsorption of silver salts on silver is dependent on the anion and is much less than a monolayer at low concentrations (38). 

The adsorption of alkali Ions (and of earth alkali ions, not shown) differs from that of the anions SO and HPO In that the latter adsorb specifically on uncharged silver Iodide, with the concomitant change In p.z.c. (sec. 3.8. fig. 3.23 -25), whereas the former do not shift the p.z.c. For alkali ions, specificity starts only when there Is already 1 on the surface. This Is an example of specific adsorption of the second kind, as defined in sec. 3.6d. Apparently, the alkali Ions only adsorb on 1 sites, so that there will be some analogy with water structure-originating alkali lon-iodlde Ion interaction In solution. We will come back to this in sec. 3.10g. 

Pergolese B, Muniz-Miranda M, Bigotto A (2005) Surface enhanced Raman scattering investigation of the halide anion effect on the adsorption of 1,2,3-triazole on silver and gold colloidal nanoparticles. J Phys Chem B 109 9665-9671... 

Colloidal dispersions owe their stability to a surface charge and the resultant electrical repulsion of charged particles. This charge is acquired by adsorption of cations or anions on the surface. For example, an ionic precipitate placed in pure water will reach solubility equilibrium as determined by its solubility product, but the solid may not have the same attraction for both its ions. Solid silver iodide has greater attraction for iodide than for silver ions, so that the zero point of charge (the isoelectric point) corresponds to a silver ion concentration much greater than iodide, rather than to equal concentrations of the two ions. The isoelectric points of the three silver halides are ° silver chloride, pAg = 4, pCl = 5.7 silver bromide, pAg = 5.4, pBr = 6.9 silver iodide, pAg = 5.5, pi = 10.6. For barium sulfate the isoelectric point seems to be dependent on the source of the product and its de ee of perfection. ... 

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