Silver phosphate

Silver orthophosphate, Ag3P04, p = 6.37 g/cc, mp = 849°C, is obtainable as an insoluble bright yellow powder from silver nitrate by the action of POCI3 (5.88), or aqueous sodium salt (14.3). It is photosensitive and turns reddish in colour, and can be reduced to metallic silver with hydrogen at 425°C. In Ag3P04 the Ag-O bonds are probably somewhat covalent, since the structure is based on tetrahedral Ag04 and PO4 units. The acid silver salt cannot be precipitated from an aqueous solution with Na2HP04 because of the relationship (5.89). 

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Zinc phosphate, Zn2(P0 2> forms the basis of a group of dental cements. Chromium and zinc phosphates are utilized in some metal-treating appHcations to provide corrosion protection and improved paint adhesion. Cobalt(II) phosphate octahydrate [10294-50-5] Co2(P0 2 8H20, is a lavender-colored substance used as a pigment in certain paints and ceramics. Copper phosphates exhibit bioactivity and are used as insecticides and fungicides. Zinc, lead, and silver phosphates are utilized in the production of specialty glasses. The phosphate salts of heavy metals such as Pb, Cr, and Cu, are extremely water insoluble. 

Silver Phosphates. Silver phosphate [7784-09-0], or silver orthophosphate, Ag3P04, is a bright yellow material formed by treating silver nitrate with a soluble phosphate salt or phosphoric acid. Silver pyrophosphate [13465-97-9], is a white salt prepared by the addition of a soluble... 

Combination silver—silver salt electrodes have been used in electrochemistry. The potential of the common Ag/AgCl (saturated)—KCl (saturated) reference electrode is +0.199 V. Silver phosphate is suitable for the preparation of a reference electrode for the measurement of aqueous phosphate solutions (54). The silver—silver sulfate—sodium sulfate reference electrode has also been described (55). 

If the dissociation constant of the acid HA is very small, the anion A- will be removed from the solution to form the undissociated acid HA. Consequently more of the salt will pass into solution to replace the anions removed in this way, and this process will continue until equilibrium is established (i.e. until [M + ] x [A-] has become equal to the solubility product of MA) or, if sufficient hydrochloric acid is present, until the sparingly soluble salt has dissolved completely. Similar reasoning may be applied to salts of acids, such as phosphoric(V) acid (K1 = 7.5 x 10-3 mol L-1 K2 = 6.2 x 10-8 mol L-1 K3 = 5 x 10 13 mol L-1), oxalic acid (Kx = 5.9 x 10-2 mol L-K2 = 6.4 x 10-5molL-1), and arsenic)V) acid. Thus the solubility of, say, silver phosphate)V) in dilute nitric acid is due to the removal of the PO ion as... 

The original method of phosphate preparation involved extracting the phosphate and reprecipitating it as a bismuth phosphate (Tudge 1960). Alternatively, it is precipitated as a silver phosphate (Wright and Hoering 1989) which involves fewer steps and, more importantly, silver phosphate is not hygroscopic (as is bismuth phosphate) which minimizes the potential for contamination by atmospheric water. 

The second analytical method uses a combustion system (O Neil et al. 1994) in place of reaction with BrF,. This method was used for the crocodiles because they were represented by very thin caps of enamel. The enamel was powdered and sieved (20 mg), pretreated in NaOCl to oxidize organic material and then precipitated as silver phosphate. Approximately 10-20 mg of silver phosphate were mixed with powdered graphite in quartz tubes, evacuated and sealed. Combustion at 1,200°C was followed by rapid cooling in water which prevents isotopic fractionation between the CO2 produced and the residual solid in the tube. Analyses of separate aliquots from the same sample typically showed precisions of 0.1%o to 0.4%o with 2 to 4 repetitive analyses even though yields are on the order of 25%. 

Tooth enamel precipitated as silver phosphate and reacted via this method gave values similar to corrected laser data from aliquots of the same tooth enamel (Table 6.1). Thus, the data from the crocodile samples are considered directly comparable with the data from the mammal tooth enamel. 

We thank the editors for including our manuscript even though we were unable to attend the conference. We thank M. Spicuzza for maintaining the laser extraction lines, J. O Neil, H. Frieke, and R. Blake for help with the silver phosphate precipitation and analysis, J. Farquhar,T. Chacko, andY. Kolodny forpro-viding standards, and J. Banfield, K. Barovich, L. Bamngartner, S. Baumgartner,... 

Silver bromide Silver chloride Silver perchlorate Silver cyanide Silver fluoride Silver iodide Silver permar>gate Silver nitrate Silver carbonate Silver oxide Silver sulphate Silver sulphide Silver phosphate... 

It has been proposed that this mixing enthalpy is of purely electrostatic origin representing a slight modification of the environment near the ions. We can, for instance, envisage dissolution of silver iodide in silver phosphate schematically as follows... 

In some procedures silver phosphate is formed by addition of silver nitrate to a slightly alkaline52 or acidic53 phosphate solution, then the precipitate is dissolved in ammoniacal potassium cyanonickelate, according to reaction 2. The displaced nickel is titrated with... 

In a different potentiometric procedure, a known excess of silver nitrate was added to the sample in a pH 7-8 buffer, the precipitated silver phosphate was removed and the remaining silver ions were determined by KBr titration50. Heavy cations which form... 

Scheme 82 shows the intramolecular version of the reaction using an alkenyl iodide in the presence of the same Pd system containing silver phosphate (194,195). The reaction can also be used for the asymmetric synthesis of quaternary carbon centers. 

Silver phosphate (Ag3P04), [CAS 7784-09-01 yellow precipitate, by reaction of silver nitrate solution and disodium hydrogen phosphate solution, soluble in HNO3 and in NH4OH, turns dark on exposure to light. 

P3N203H4lprismatic crystals, neutral to litmus, while penta-sodium diimidotriphosphate has an alkaline reaction. The trisilver salt forms monoclinic crystals. Warming the pentasilver salt with ammonium nitrate destroys the yellow colour—yellow silver phosphate is not whitened by this treatment, while silver trimetaphosphimate becomes orange-yellow. The empirical composition of the acid corresponds with either ... 

The deposition of silver in tissues is the result of the precipitation of insoluble silver salts, such as silver chloride and silver phosphate. These insoluble silver salts appear to be transformed into soluble silver sulfide albuminates, to bind to or form complexes with amino or carboxyl groups in RNA, DNA, and proteins, or to be reduced to metallic silver by ascorbic acid or catecholamines (Danscher 1981). The blue or gray discoloration of skin exposed to ultraviolet light in humans with argyria may be caused by the photoreduction of silver chloride to metallic silver. The metallic silver is then oxidized by tissue and bound as black silver sulfide (Danscher 1981). Bucklet et al. (1965) identified silver particles deposited in the dermis of a woman with localized argyria as being composed of silver sulfide. 

The discoloring is likely to be caused by the photoreduction of silver chloride and/or silver phosphate in the skin. X-ray dispersive analysis of skin and other tissues reveals that the granules consist of silver complexed with sulfur and/or selenium. The photoreduced deposits are not removed by the body, and there are no clinical means of removing them. 

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