Silver arsenate, 318— arsenite

Arsenites may also be determined by this procedure but must first be oxidised by treatment with nitric acid. Small amounts of antimony and tin do not interfere, but chromates, phosphates, molybdates, tungstates, and vanadates, which precipitate as the silver salts, should be absent. An excessive amount of ammonium salts has a solvent action on the silver arsenate. 

Silver nitrate solution brownish-red precipitate of silver arsenate Ag3As04 from neutral solutions (distinction from arsenite and phosphate which yield yellow precipitates), soluble in acids and in ammonia solution but insoluble in acetic acid. 

If the acidity of the filtrate from 2 is reduced (to about pH 5) by just neutralizing with sodium hydroxide solution and adding dilute acetic acid, silver nitrate solution will precipitate phosphate, arsenate, arsenite, oxalate, and possibly other organic acids. 

NITRIC ACID, SILVER(I) SALT (7761-88-8) A powerful oxidizer. Forms friction- and shock-sensitive compounds with many materials, including acetylene, anhydrous ammonia (produces compounds that are explosive when dry), 1,3-butadiyne, buten-3-yne, calcium carbide, dicopper acetylide. Contact with hydrogen peroxide causes violent decomposition to oxygen gas. Violent reaction with chlorine trifluoride, metal powders, nitrous acid, phospho-nium iodide, red or yellow phosphorus, sulfur. Incompatible with acetylides, acrylonitrile, alcohols, alkalis, ammonium hydroxide, arsenic, arsenites, bromides, carbonates, carbon materials, chlorides, chlorosulfonic acid, cocaine chloride, hypophosphites, iodides, iodoform, magnesium, methyl acetylene, phosphates, phosphine, salts of antimony or iron, sodium salicylate, tannic acid, tartrates, thiocyanates. Attacks chemically active metals and some plastics, rubber, and coatings. 

S Silver, K Budd, KM Leahy, WV Shaw, D Hammond, RP Novick, GR Willsky, MH Malamy, H Rosenberg. Inducible plasmid-determined resistance to arsenate, arsenite and antimony (III) in Escherichia cofi and Stapfiylococcus aureus. J Bacteriol 146 983-996, 1981. 

Arsenates are precipitated in neutral solution as silver arsenate, Ag3As04, reddish brown, having the same solubihties as the arsenite. 

With the salts of certain weak acids, such as carbonic, sulphurous, and nitrous acids, an additional factor contributing to the increased solubility is the actual disappearance of the acid from solution either spontaneously, or on gentle warming. An explanation is thus provided for the well-known solubility of the sparingly soluble sulphites, carbonates, oxalates, phosphates(V), arsenites(III), arsenates(V), cyanides (with the exception of silver cyanide, which is actually a salt of the strong acid H[Ag(CN)2]), fluorides, acetates, and salts of other organic acids in strong acids. 

Ji G, S Silver (1992) Reduction of arsenate to arsenite by the ArsC protein of the arsenic resistance operon of Staphylococcus aureus plasmid pl258. Proc Natl Acad Sci USA 89 9474-9478. 

Arsenic acid reacts with metal salts forming their orthoarsenates, e.g., calcium orthoarsenate. Reaction with silver nitrate in neutral solution produces a chocolate-brown precipitate of silver orthoarsenate. It forms pyroarsenic acid (or pyroarsenate) on heating over 100°C. It is reduced to arsenous acid (or arsenites) when treated with reducing agents. 

Pour a sodium arsenite solution into two test tubes, add a silver nitrate solution to one of them and iodine water to the other. What is observed Write the equations of the reactions. What properties of arsenous acid are revealed by the performed experiments ... 

With sodium thiosulphate the arsenite forms oxythioarsenates (see p. 282), as it also does with tri- and tetra-thionates sodium dithionate does not react either in cold or boiling solution. Sodium tellurate causes oxidation to arsenate.1 An ammoniacal solution of silver azide is reduced to silver by sodium arsenite other metallic azides do not react. 

Some of the volumetric methods described above may also be adapted to the electrometric determination of arsenic. Such methods have been described for titration of arsenites with ceric sulphate,9 iodine in the presence of sodium bicarbonate,10 chloramine (p-toluene-sulphone chloramide),11 alkaline potassium ferricyanide solution,12 potassium bromate13 or potassium iodate14 in the presence of hydrochloric acid, silver nitrate15 (by applying a secondary titration with 01N alkali to maintain the desired low H+-ion concentration), and with... 

Silver nitrate yellow precipitate of silver arsenite in neutral solution (distinction from arsenates) ... 

The reactions with silver nitrate solution are intended to act as a guide to the presence of groups of anions, and the table must be interpreted in conjunction with the observations made in the preliminary tests. Arsenite, arsenate, and chromate will be found in the analysis for cations (Section VI.8). 

Separations of various anions Using a solvent mixture composed of n-butyl alcohol, pyridine, and 1-5m ammonia solution in the proportions of 2 1 2, the following Rf values are obtained for the sodium or potassium salts chloride, 0-24 bromide, 0-36, iodide, 0-47 chlorate, 042, bromate, 0-25, iodate, 0-09 nitrite, 0-25 nitrate, 0-40 arsenite, 019 arsenate, 0 05 phosphate, 0-04 and thiocyanate, 0 56. The positions of the anions may be detected by spraying with ammoniacal silver nitrate potassium iodide and hydrochloric acid are particularly effective for chlorates, bromates, and iodates. The RF values provide the basis for the separation of a number of mixtures of anions, e.g. chloride and iodide, bromide or iodide and nitrate. 

Osmium tetraoxide (osmic acid) Pentachlorophenol Perchloric acid Phosphorus pentasulfide Phosphorus pentoxide Phosphorus, red Phosphorus, yellow or white Picric acid, trinitrophenol Potassium cyanide Potassium perchlorate Potassium sulfide Potassium, metal Pyridine flammable Selenium Silver oxide Silver cyanide Sodium metal lump Sodium arsenate Sodium arsenite Sodium azide... 

Thus the activation of the Pst system during the arsenic stress confers higher levels of arsenate resistance by virtue of reduced uptake of arsenate (Silver and Nakahara, 1983). Arsenite, in contrast, appears mostly unionized as As(OH)3 at neutral pH, with a pKa of 9.3 for dissociation to H2ASO3 (Ni Dhubhghaill and Sadler, 1991). 

Trimetho.xyarsine was first reported by Crafts. It was obtained by three methods from silver arsenite and methyl iodide, from arsenic trioxide and tetramethoxysilane, and from arsenic trihalide and sodium methox ide. Better yields have been obtained by applying the method of this synthesis the procedure seems to be generally applicable to the preparation of trialkoxyarsines. 

Puschel and Stefanac ° use alkaline hydrogen peroxide in the oxygen flask method to oxidize arsenic to arsenate. The arsenate is titrated directly with standard lead nitrate solution with 4-(2-pyridylazo) resorcinol or 8-hydroxy-7-(4-sulpho-l-naphthylazo) quino-line-5-sulphonic acid as indicator. Phosphorus interferes in this method. The precision at the 99% confidence limit is within 0.67% for a 3-mg sample. In another variation, Stefanac used sodium acetate as the absorbing liquid, and arsenite and arsenate are precipitated with silver nitrate. The precipitate is dissolved in potassium nickel cyanide (K2Ni(CN)4) solution and the displaced nickel is titrated with EDTA solution, with murexide as indicator. The average error is within + 0.19% for a 3-mg sample. Halogens and phosphate interfere in the procedure. 

The growth of the bacterium is inhibited by benzoic acid, sorbate, and sodium laurylate (Onysko et al., 1984), and nitrate at 50 mM inhibits completely the oxidation of ferrous ion by the bacterium (Eccleston et al., 1985). Although the bacterium is sensitive to chloride ion, it becomes resistant to 140 pM chloride ion by training (Shiratori and Sonta, 1993). The bacterium is fairly resistant to heavy metal ions its activity to oxidize ferrous ion is scarcely inhibited in the presence of 65 mM cupric ion, 100 mM nickel ion, 100 mM cobalt ion, 100 mM zinc ion, 100 mM cadmium ion, and 0.1 mM silver ion (Eccleston et al., 1985). The bacterium acquires the ability to grow even in the presence of 2 mM uranyl ion (Martin et al., 1983). Furthermore, it becomes resistant to arsenate and arse-nite by training a strain of the bacterium has been obtained which oxidizes ferrous ion in the presence of 80 mM arsenite and 287 mM arsenate (Collinet and Morin, 1990 Leduc and Ferroni, 1994). The resistant ability of the bacterium to arsenite and arsenate is important when they are applied for the solubilization of arsenopyrite (FeAsS) [reactions (5.8) and (5.9)]. Leptospirillum ferrooxidans is generally more sensitive to heavy metal ions than A. ferrooxidans (Eccleston et al., 1985). 

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