Chemical elements
  Arsenic
      Occurrence
      Ubiquity
      History
    Isotopes
    Energy
    Production
    Application
    Physical Properties
    Chemical Properties
      Aluminium Arsenide
      Antimony Arsenides
      Barium Arsenide
      Bismuth Arsenides
      Cadmium Arsenides
      Calcium Arsenide
      Cerium Arsenide
      Chromium Arsenides
      Cobalt Arsenides
      Copper Arsenides
      Gold Arsenides
      Iridium Arsenide
      Iron Arsenides
      Lead Arsenides
      Lithium Arsenide
      Magnesium Arsenide
      Manganese Arsenides
      Mercury Arsenides
      Molybdenum Arsenide
      Nickel Arsenides
      Niobium Arsenide
      Palladium Di-arsenide
      Platinum Arsenides
      Potassium Arsenides
      Rhodium Arsenide
      Ruthenium Arsenide
      Silver Arsenides
      Sodium Arsenide
      Strontium Arsenide
      Thallium Arsenide
      Tin Arsenides
      Tungsten Arsenide
      Uranium Arsenide
      Zinc Arsenides
      Arsenic Subhydride
      Arsenic Monohydride
      Arsenic Trihydride
      Arsenic Trifluoride
      Arsenic Pentafluoride
      Arsenic Nitrosyl Hexafluoride
      Arsenic Trichloride
      Arsenic Oxychloride
      Arsenic Pentachloride
      Arsenic Tribromide
      Arsenic Oxybromide
      Arsenic Moniodide
      Arsenic Diiodide
      Arsenic Triiodide
      Arsenic Pentiodide
      Arsenic Suboxide
      Arsenious Oxide
      Aluminium Arsenite
      Ammonium Arsenites
      Antimony Arsenite
      Barium Arsenites
      Beryllium Arsenite
      Bismuth Arsenite
      Cadmium Arsenites
      Calcium Arsenites
      Chromic Arsenite
      Cobalt Arsenites
      Copper Arsenites
      Gold Arsenites
      Iron Arsenites
      Lead Arsenites
      Lithium Arsenite
      Magnesium Arsenites
      Manganese Arsenites
      Mercury Arsenites
      Nickel Arsenites
      Palladium Pyroarsenite
      Platinum Arsenites
      Potassium Arsenites
      Arsenites of Rare Earth Metals
      Rubidium Metarsenite
      Silver Arsenites
      Sodium Arsenites
      Strontium Arsenites
      Thallous Orthoarsenite
      Tin Arsenites
      Titanyl Tetrarsenite
      Tungsto-arsenites
      Uranyl Metarsenite
      Zinc Arsenites
      Zirconium Arsenite
      Arsenic Tetroxide
      Arsenic Pentoxide
      Aluminium Arsenates
      Ammonium Arsenates
      Barium Arsenates
      Beryllium Arsenates
      Bismuth Arsenates
      Cadmium Arsenates
      Caesium Arsenate
      Calcium Arsenates
      Chromium Arsenates
      Cobalt Arsenates
      Copper Arsenates
      Hydroxylamine Orthoarsenate
      Iron Arsenates
      Lead Arsenates
      Lithium Arsenates
      Magnesium Arsenates
      Manganese Arsenates
      Mercury Arsenates
      Molybdenum Arsenates
      Nickel Arsenates
      Palladium Arsenate
      Platinic Arsenate
      Potassium Arsenates
      Rare Earth Metals Arsenates
      Rhodium Arsenate
      Rubidium Arsenates
      Silver Arsenates
      Sodium Arsenates
      Strontium Arsenates
      Thallium Arsenates
      Thorium Arsenates
      Tin Arsenates
      Titanyl Arsenate
      Tungsto-arsenic Acids
      Uranium Arsenates
      Vanado-arsenates
      Zinc Arsenates
      Zirconium Arsenates
      Perarsenates
      Arsenic and Sulphur
      Arsenic Subsulphide
      Tetrarsenic Trisulphide
      Arsenic Disulphide
      Arsenic Trisulphide
      Arsenic Pentasulphide
      Thioarsenates
      Ammonium Thioarsenates
      Antimony Thioarsenate
      Barium Thioarsenates
      Beryllium Thioarsenate
      Bismuth Thioarsenate
      Cadmium Thioarsenates
      Calcium Thioarsenates
      Cerium Thioarsenates
      Chromium Thioarsenate
      Cobalt Thioarsenate
      Copper Thioarsenates
      Gold Thioarsenates
      Iron Thioarsenates
      Lead Thioarsenates
      Lithium Thioarsenates
      Magnesium Thioarsenates
      Manganese Thioarsenates
      Mercury Thioarsenates
      Molybdenum Thioarsenates
      Nickel Thioarsenates
      Platinic Thioarsenate
      Potassium Thioarsenates
      Silver Thioarsenates
      Sodium Thioarsenates
      Strontium Thioarsenates
      Thallium Orthothioarsenate
      Tin Thioarsenates
      Uranyl Thioarsenate
      Yttrium Thioarsenate
      Zinc Thioarsenates
      Zirconium Thioarsenate
      Trioxythioarsenic Acid
      Dioxydithioarsenic Acid
      Oxytrithioarsenic Acid
      Arsenic Monosulphatotrioxide
      Arsenic Disulphatotrioxide
      Arsenic Trisulphatotrioxide
      Arsenic Tetrasulphatotrioxide
      Arsenic Hexasulphatotrioxide
      Arsenic Octasulphatotrioxide
      Complex salts of Sulphato-compounds of Arsenic
      Arsenic Nitride
      Arsenic Imide
      Arsenic Amide
      Arsenic Phosphides
      Arsenic oxyphosphides
      Arsenic Phosphate
      Arsenic Thiophosphate
      Arsenic Tricarbide
      Arsenic Pentasilicide
      Boron Arsenate
    Detection of Arsenic
    Estimation of Arsenic
    Physiological Properties
    PDB 1b92-1ihu
    PDB 1ii0-1tnd
    PDB 1tql-2hmh
    PDB 2hx2-2xnq
    PDB 2xod-3htw
    PDB 3hzf-3od5
    PDB 3ouu-9nse

Trioxythioarsenic Acid, H3NaO3S






Trioxythioarsenic Acid, H3NaO3S, is formed in solution when hydrogen sulphide is passed into a cold, dilute, acidified solution of potassium orthoarsenate. Excess of the gas should be avoided but, if present, may be removed either by immediate addition of copper sulphate, or by a vigorous stream of air. Any opalescence due to sulphur may be removed by adding asbestos and filtering. The solution obtained gives no immediate precipitate with hydrogen sulphide, but sulphur ultimately appears. When the solution is boiled, pure sulphur is precipitated, but no hydrogen sulphide or sulphur dioxide is evolved; on cooling, passage of hydrogen sulphide gives an immediate precipitate of arsenious sulphide.

Trioxythioarsenates of ammonium, the alkali metals and the alkaline earth metals have been prepared. Those of the heavy metals are unstable and difficult to isolate; the precipitates obtained when the salts of such metals are treated with a solution of an alkali trioxythio-arsenate undergo immediate decomposition, yielding sulphides.


Ammonium Trioxythioarsenate, (NH4)3NaO3S

Ammonium Trioxythioarsenate, (NH4)3NaO3S.3H2O, may be obtained by heating under pressure on a water-bath an aqueous solution of ammonium arsenite containing the calculated amount of fine sulphur; thioarsenate and arsenate are also formed and the thioxy-salt may be separated by fractional crystallisation from aqueous alcohol. It yields small, colourless plates, which are readily soluble in water. The crystals lose ammonia when kept in air, and the solution also loses ammonia on boiling, the salt being decomposed with formation of arsenious oxide and sulphur. A tetrahydrate, (NH4)3AsO3S.4H2O, has been obtained by melting together equal parts of arsenious oxide and sulphur and digesting the residue with aqueous ammonia; after keeping the liquid for 24 hours, it was filtered and the filtrate treated with alcohol. An oil separated which, when cooled in ice, set to a white crystalline mass, with properties similar to the trihydrate. The mother liquor from which the oil had separated, on addition of more alcohol, yielded a crystalline precipitate of ammonium monohydrogen trioxythioarsenate, (NH4)2HNaO3S. The crystals turned yellow in air with loss of ammonia, but m an atmosphere of ammonia the white colour was restored.The normal sodium and potassium salts, Na3NaO3S.12H2O and K3NaO3S.2H2O, may be prepared by treating a concentrated solution of the alkali arsenite with sodium thiosulphate at the ordinary temperature. Heat is developed and, in the case of the sodium salt, the trioxythioarsenate crystallises out and sodium sulphite remains in the solution:

Na3NaO3 + Na2S2O3 = Na3NaO3S + Na2SO3

A small quantity of arsenic also separates. In the case of the potassium salt, however, the sulphite is first crystallised out and the trioxythioarsenate then obtained by evaporating the mother liquor over sulphuric acid. The alkali monohydrogen arsenites also yield the above salts, in the cold, with sodium thiosulphate.

Sodium Monohydrogen Trioxythioarsenate, Na2HNaO3S

Sodium Monohydrogen Trioxythioarsenate, Na2HNaO3S.8H2O, has been obtained as colourless triclinic crystals by fractionally crystallising the liquid resulting when arsenious oxide is boiled with aqueous sodium sulphide; the normal trioxythioarsenate, as well as sodium dioxythioarsenate, Na3AsO2S2.10H2O, and sodium orthoarsenate, were also obtained from the solution. The corresponding potassium salt, K2HNaO3S.2.5H2O, has been prepared by adding a slight excess more than the theoretical quantity) of potassium hydroxide to a solution of the dihydrogen salt and allowing the mixture to crystallise over sulphuric acid and potassium hydroxide. It yields colourless, very hygroscopic prisms.

Sodium Dihydrogen Trioxythioarsenate, NaH2NaO3S

Sodium Dihydrogen Trioxythioarsenate, NaH2NaO3S.H2O, is formed when the normal salt, Na3NaO3S.12H2O (1 mol.), is triturated, without addition of water, with salicylic acid (2 mols.) and the product treated with alcohol in a closed vessel until the presence of salicylic acid can no longer be detected. The salt is freed from any remaining normal salt by levigation. It forms colourless prismatic crystals which give an acid reaction with moist litmus paper. It is unstable and decomposes with separation of sulphur, both in the dry state and in the presence of water:

NaH2NaO3S = NaAsO2 + H2O + S

The decomposition is accelerated by heat. The corresponding potassium salt, KH2NaO3S.H2O,hasbeen obtained by the action of hydrogen sulphide on a cold aqueous solution of potassium mono- or di-hydrogen orthoarsenate, and also by digesting arsenious sulphide in a concentrated solution of potassium carbonate, or by the method described above for the sodium salt. The salt is colourless, stable in air, sparingly soluble in cold water but more soluble in hot. It loses water when heated at 170° C. and at a higher temperature melts and then decomposes. The hot solution also undergoes some decomposition.
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