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

Lead Arsenates





Lead Orthoarsenate, Pb3(AsO4)2

Lead Orthoarsenate, Pb3(AsO4)2, is formed when a mixture of arsenious oxide and lead monoxide is heated at 450° to 800° C. It is difficult to obtain in a pure state by precipitation, but products approximating in composition to it are obtained when solutions of lead salts are added to alkali hydrogen arsenates. It appears to be unstable and to exist only under limited conditions.

The anhydrous salt yields yellowish-white crystals of density 7.3 at 15° C. and melting point 1042° C. The specific heat is 0.0728 and the molar heat 65.4. The index of refraction is 2.14. It is insoluble in water, aqueous ammonia and in solutions of ammonium salts, and only slightly soluble in aqueous alkali or brine. It is decomposed when heated with hydrogen chloride, forming lead and arsenic chlorides, and in hot nitric acid it dissolves to form arsenic acid and lead nitrate, the latter being precipitated if the acid is sufficiently concentrated.


Lead Monohydrogen Orthoarsenate, PbHAsO4

Lead Monohydrogen Orthoarsenate, PbHAsO4, is deposited in the form of white crystalline needles when a boiling solution of the normal arsenate in nitric acid is diluted with water or treated with a dilute solution of ammonia. It is also obtained by the prolonged action of arsenic acid and air upon metallic lead, or by decomposing aqueous lead nitrate with arsenic acid or sodium monohydrogen arsenate. It has been found as a mineral in S.W. Africa and named schultenite; the colourless monoclinic crystals have axial ratios a:b:c = 0.8643:1:0.7181, β = 84°36', and indices of refraction along the three axes α 1.8903, β 1.9077 and γ 1.9765. When heated above 280° C. lead pyroarsenate is formed, which fuses at a bright red heat.

The monohydrogen arsenate is insoluble in cold water and only very slightly soluble on long contact with boiling water, but the prolonged action of cold water converts it to a basic arsenate of composition Pb5(OH)(AsO4)3. It is attacked by halogen acids and salts and by nitric acid.

Commercial lead arsenate usually consists mainly of the monohydrogen arsenate, but may also contain the normal arsenate. It is in great demand as an insecticide. Many methods of manufacture are described in the patent literature, some of the more recent being as follows: (1) Metallic lead and arsenious oxide are added to a concentrated solution of arsenic acid containing nitric acid; lead arsenate is precipitated, the concentration of the arsenic acid remaining constant. At intervals the precipitate is removed and the arsenic acid solution again treated. (2) A solution of a soluble arsenate is treated with lead chloride to cause partial conversion to lead arsenate and the reaction completed by adding lead nitrate. (3) Steam is passed into a chamber in which a mixture of litharge and arsenious oxide is heated. (4) Lead fluosilicate is heated with a metallic arsenate, for example:

3PbSiF6 + 2CaHAsO4 = Pb3(AsO4)2 + 2CaSiF6 + H2SiF6

Lead arsenate may also be obtained electrolytically by the anodic dissolution of lead in the presence of an arsenate. An almost theoretical yield has been obtained by using a diaphragm cell with an anolyte containing 20 g. sodium arsenite and 70 g. sodium nitrate per litre and sufficient acetic acid for neutralisation, and a catholyte consisting of a 30 per cent, solution of sodium nitrate. The anode should be of lead and the cathode of iron, and the current density 5.5 to 6 amps, per sq. dm.

Lead Dihydrogen Orthoarsenate, Pb(H2AsO4)2

Lead Dihydrogen Orthoarsenate, Pb(H2AsO4)2, may be obtained from the monohydrogen salt by boiling with a solution of arsenic acid of 86 per cent, concentration; the boiling temperature is about 130° C. and the crystals which form on cooling are removed by centrifuging, washed with alcohol and dried at 110° C. The product usually contains a slight excess of arsenic acid.

The crystals appear to be triclinic; the indices of refraction for sodium light at 20° C. are α = 1.74, β = 1.84 and γ = 1.82. The salt loses water when heated, the equivalent of 1 molecule being lost on prolonged heating at 150° C., when lead hydrogen pyroarsenate, PbH2As2O7, is probably formed, and the whole expelled below red heat; when fusion occurs some arsenious oxide vapour is emitted.

A phase rule study of the system PbO-As2O5-H2O has been made over the acid range at 25° C. and the conditions for the existence of the two acid lead arsenates defined.

Lead Pyroarsenate, Pb2As2O7

Lead Pyroarsenate, Pb2As2O7, is formed when the monohydrogen orthoarsenate is heated above 280° C., or by fusing together lead oxide and arsenic pentoxide or potassium metarsenate, or by precipitating lead acetate solution by addition of sodium pyroarsenate. The fused product forms colourless lamellae of density 6.85 at 15° C. and melting point 802° C. In contact with water it becomes opaque and the monohydrogen orthoarsenate is formed.

Lead Metarsenate, Pb(NaO3)2

Lead Metarsenate, Pb(NaO3)2, is obtained by heating a mixture of arsenic pentoxide and lead monoxide, red lead or lead nitrate in suitable proportions. A transparent glass is formed which, if broken up and heated to incipient fusion, crystallises as hexagonal tablets of density 6.42. The salt is decomposed by water.

Mixed salts of composition PbNaAsO4 and PbKAsO4 have been obtained by dissolving litharge in molten mixtures of the alkali orthoarsenate and chloride; from fused sodium metarsenate in which 15 per cent, of litharge was dissolved, crystals of composition 4PbO.2Na2O.3As2O5 or Pb4Na4(As2O7)3 have been obtained.

The mineral mimetite, 3Pb3(AsO4)2.PbCl2, may be prepared artificially by fusing a mixture of its component salts. It occurs in yellow to brown crystal aggregates or mammillary crusts. The crystals are hexagonal pyramids, a:c = 0.73147, isomorphous with pyromorphite and the apatites. It is widely distributed and has been found in Cornwall, Cumberland and Leadhills (Lanark).
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