Sodium orthoarsenate

Aluminium Arsenates.—The orthoarsenate, A1As04, is obtained 2 in the form of elongated lens-shaped crystals when normal sodium orthoarsenate is heated with an excess of aluminium sulphate in a sealed tube at 220° C. The crystals are hexagonal in structure, with a0 = 5-030 and c0 = 5-612 A. the form is similar to that of quartz.3... 

Cadmium Arsenates.—The hydrated normal cadmium orthoarsenate, 2Cd3(As04)2.3H20, falls as a white voluminous precipitate on adding alkali to a solution of cadmium mono- or di-hydrogen arsenate in hydrochloric acid,4 or on addition of sodium orthoarsenate to a solution of cadmium sulphate.5 On drying at 100° C. the anhydrous salt remains. 

Colloidal cobalt arsenate has been obtained in the form of an opalescent jelly either by mixing in the cold a solution of a cobalt salt of a strong acid with potassium dihydrogen orthoarsenate,8 or by successively treating an aqueous solution of a cobaltous salt with ammonium sulphate, acetic acid and an excess of sodium orthoarsenate.9... 

Gold Arsenate is precipitated as a yellowish-white powder when sodium orthoarsenate is added to a hot solution of auric chloride.12... 

Manganese Arsenates.—Manganous Orthoarsenate, Mns(As04)a. H20, is obtained as brown needles 8 when manganese sulphate is heated with sodium orthoarsenate in a sealed tube at 175° C. 

Palladium Arsenate was reported by Berzelius3 as a pale yellow precipitate formed when sodium orthoarsenate was added to a neutral solution of palladious nitrate. 

Sodium orthoarsenate is also obtained electrolytically by the method described under calcium arsenate (p. 198). Yields up to 100 per cent, may be obtained 9 by employing a cell with a diaphragm between iron electrodes. The anolyte should contain sodium arsenite, or sodium hydroxide and arsenious oxide (equivalent to 150 g. As2Os per litre), and the catholyte sodium hydroxide (150 g. per litre). With a current density of 3 amps, per sq. dm. the current efficiency is 100 per cent. A solid crust of sodium arsenate forms around the anode. The process may be rendered continuous by circulating the anolyte and removing the precipitated arsenate. Iron or nickel electrodes are... 

The density2 of anhydrous sodium orthoarsenate is 2-835. From solution it crystallises as the dodecahydrate, Na3As04.12H20, of density 3 1-76 and melting point 85-5° C. The crystals are hexagonal prisms, isomorphous with the corresponding phosphate. The following refractive indices have been determined 4... 

The heat of formation of sodium orthoarsenate in aqueous solution from the elements is 381,500 calories,1 and that of the solid 360,800 calories.2 The heat of neutralisation (3Na0H.H3As04.aq.) is 35,920 calories,8 and the heat of formation from the oxides is 2... 

In cold aqueous solution, sodium orthoarsenate reacts with sodium hydrosulphite to form sodium arsenohydrosulphite,6 NagAs(S204)3, a creamy white granular powder. In the presence of sodium sulphite this compound decomposes, forming sodium arsenothiosulphate, an unstable intermediate product, and finally arsenious sulphide.7 If the reduction by sodium hydrosulphite takes place in the presence of hydrochloric acid, some arsenic subsulphide, As3S, is also precipitated,8 and this product is also obtained when the orthoarsenate in aqueous solution is treated with phosphorus trichloride and the mixture saturated with sulphur dioxide.9... 

A basic stannic pyroarsenate, SnAs2O7.SnO3.10H2O, is obtained when the white gelatinous precipitate formed by boiling a solution containing sodium stannate, excess of sodium orthoarsenate and nitric acid, is dried at the ordinary temperature.4 The salt becomes anhydrous at 120Q C. 

SYNS FATSCO ant poison sodium ARSENATE (DOT) SODIUM MET. ARSENATE SODIUM ORTHOARSENATE SWEENEY S ANT-GO... 

Synonyms Arsenic acid, sodium salt Sodium metaarsenate Sodium orthoarsenate Empirical AsH304 xNa Properties Colorless clear cryst. odorless mild alkaline taste sol. in water si. sol. in 95% ethanol, glycerol insol. in ether m.w. 302.88 sp.gr. 

Sodium orthoarsenate. See Sodium arsenate Sodium oxalate... 

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