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

Sodium Arsenites






It is difficult to obtain arsenites of sodium in the crystalline state and there is some doubt as to the possibility of preparing them in a pure form. A study of the ternary system Na2O-As2O3-H2O at 30° C. suggests the existence of solid arsenites of composition NaAsO2, Na4As2O5 and Na10As4O11.26H2O. As the proportion of alkali in the solution increases, the solubility of the arsenious oxide increases rapidly. By digesting the latter with excess of alcoholic sodium hydroxide and extracting with alcohol, a product approximating in composition to sodium orthoarsenite, Na3NaO3, has been obtained, and Vanzetti, in an attempt to obtain this compound in the absence of water, dissolved arsenious oxide in a methyl alcohol solution of sodium methoxide, using quantities in accordance with the reaction

As2O3 + 6NaOCH3 = 2Na3NaO3 + 3(CH3)2O

The excess of alcohol was evaporated off to give a syrup, which was then left to crystallise in a vacuum desiccator containing calcium chloride. The crystals formed were highly hygroscopic and varied in composition, the arsenic content diminishing from about 80 per cent, in the first fractions to about 20 per cent, in the last of that required by the formula Na3NaO3. Very little ether was apparently liberated during the reaction, which did not go to completion. The crystals were white, dissolved readily in water, and the solution with silver nitrate gave a precipitate of yellow silver orthoarsenite.

The equivalent electrical conductivity of the aqueous solution has been determined by several investigators. Walden, using solutions containing one-third of a mole of Na3NaO3 in v litres, obtained the following values:

v32641282565121024
Λ158.3160.1161.1160.6156.7154.3


Using the dihydrogen salt, NaH2NaO3, von Zawidzki determined the equivalent conductivity in the presence of N/32 arsenious acid in order to diminish hydrolytic dissociation, and concluded that it resembled the salt of a monobasic acid. At extreme dilutions the equivalent conductivity increased, apparently owing to hydrolysis and oxidation. This view that arsenious acid is essentially a feeble monobasic acid is supported by Thomsen's thermochemical values for the heats of neutralisation of the acid.

The aqueous solution of sodium arsenite undergoes slow oxidation when exposed to the air; but according to Reinders and Vies, this can only proceed in the presence of a catalyst. Suitable catalysts are finely divided copper and copper salts; the former dissolves in a cold solution of sodium arsenite in the presence of oxygen. Oxidation may readily be effected at the ordinary temperature by passing air through a solution of the arsenite containing in suspension copper powder, cuprous oxide, cuprous chloride, zinc dust or yellow phosphorus. The oxidation is more readily effected in the presence of a second easily oxidisable substance, such as stannous chloride, manganous or cobaltous hydroxide, or sodium sulphite; with the last-named the oxidation of the arsenite is not induced if the solution is strongly alkaline. The oxidation of the added substance may be retarded by the presence of the sodium arsenite; this is the case with stannous salts, sulphites, phosphorus, chloroform and certain aldehydes. The arsenite is also oxidised in aqueous solution by nitric oxide,

Na3NaO3 + 2NO = Na3AsO4 + N2O

and by hydroxylamine,

Nitrogen is also evolved due to simultaneous decomposition of hydroxylamine as follows:

3NH2OH = NH3 + N2 + 3H2O

With sodium thiosulphate the arsenite forms oxythioarsenates, 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. An ammoniacal solution of silver azide is reduced to silver by sodium arsenite; other metallic azides do not react.

Sodium orthoarsenite is converted largely to arsenate and free arsenic when heated in an inert atmosphere; slow heating below 300° C. causes loss of arsenious oxide. Fusion with sodium hydroxide causes conversion to arsenate.

Schreinemakers and de Baat's study of the system Na2O-As2O3-H2O afforded evidence of the formation of sodium pyroarsenile, Na4As2O5, both in the anhydrous state and as the hydrated salt, Na4As2O5.9H2O, but the isolation of these compounds in a pure form is difficult.


Sodium Metarsenite, NaAsO2

Sodium Metarsenite, NaAsO2, may be prepared by boiling an aqueous solution of sodium carbonate with an excess of arsenious oxide and evaporating the solution to dryness. It is a white powder which, when heated, yields arsenic and sodium arsenate. It undergoes oxidation by atmospheric oxygen under pressure, and determinations of the velocity of the reaction at 100° to 250° C. show it to be a reaction of the first order. The addition of sodium metarsenite to excess of a solution of a metallic salt generally causes precipitation, but the composition of the precipitate varies with the nature of the salt. Thus the orthoarsenite is obtained with nickel and lead nitrates, zinc sulphate and stannous chloride. With stannic chloride a basic arsenite, 7SnO2.As2O3, is formed. Cobalt nitrate and cadmium sulphate yield the corresponding pyroarsenites; metarsenites do not appear to be precipitated by this means.
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