Chemical elements
  Lead
    Occurrence
    Isotopes
    Energy
    Production
    Application
    Physical Properties
    Chemical Properties
      Lead Tetramethyl
      Lead Tetraethyl
      Lead Tetraphenyl
      Lead Ethoxide
      Lead Fluoride
      Lead Tetrafluoride
      Hydrofluoplumbic Acid
      Lead Chloride
      Lead Chloride Double Salts
      Basic Lead Chlorides
      Lead Tetrachloride
      Ammonium Plumbichloride
      Lead Chlorite
      Lead Chlorate
      Lead Perchlorate
      Lead Dibromide
      Double Salts of Lead Bromide
      Basic Lead Bromides
      Lead Bromate
      Lead Iodide
      Lead Iodide Complex Salts
      Basic Lead Iodides
      Lead Tetra-iodide
      Lead Iodate
      Lead Periodates
      Lead Suboxide
      Lead Monoxide
      Litharge
      Massicot
      Lead Hydroxides
      Lead Dioxide
      Plumbic Acids
      Hexahydroxyplumbic Acid
      Colloidal Plumbic Acid
      Potassium Plumbate
      Lead Plumbate
      Calcium Orthoplumbate
      Lead Orthoplumbate
      Red Lead
      Metaplumbic Acid
      Calcium Metaplumbate
      Lead Metaplumbate
      Basic Lead Plumbate
      Lead Sulphide
      Lead Sulphohalides
      Lead Polysulphide
      Lead Sulphite
      Lead Sulphates
      Lead Sulphate
      Basic Lead Sulphates
      Lead Hydrogen Sulphate
      Plumbic Sulphate
      Lead Persulphate
      Lead Thiosulphate
      Lead Dithionate
      Lead Selenide
      Lead Selenite
      Lead Selenate
      Lead Telluride
      Lead Tellurite
      Lead Azide
      Lead Azoimide
      Lead Hydrazoate
      Lead Imide
      Lead Hyponitrite
      Lead Nitrites
      Lead Nitrate
      Lead saltpetre
      Basic Lead Nitrates
      Lead Hypophosphite
      Lead Phosphite
      Lead Orthophosphate
      Lead Monohydrogen Phosphate
      Lead Dihydrogen Phosphate
      Lead Pyrophosphate
      Lead Metaphosphate
      Lead Arsenite
      Lead Orthoarsenate
      Lead Hydrogen Arsenate
      Lead Pyroarsenate
      Lead Antimonate
      Lead Carbonate
      White Lead
      Lead Formate
      Lead Acetate
      Sugar of Lead
      Complex Lead Acetates
      Plumbic Acetate
      Lead Tetra-acetate
      Lead Oxalate
      Lead Tartrate
      Lead Silicates
      Lead Borates
      Normal Lead Chromate
      Lead Dichromate
      Basic Lead Chromate
      Lead Molybdate
      Lead Tungstate
      Lead Metatungstate
      Lead Diuranate
      Lead Peruranate
    PDB 1afv-3qjk

Lead Sulphide, PbS






Lead Sulphide, PbS, occurs in nature, and is the principal ore of lead. This ore has been known since the time of the ancients as galena, but that it contained sulphur was not recognized till modern times, although Boyle was aware that lead could be obtained from it by heating it with scrap-iron. Another name for the ore is lead glance. It occurs in dark grey masses, having a metallic lustre, crystallised in regular cubes or octahedra, and shows a well-defined cubic cleavage. Galena has a hardness of 2.5 and a density of 7.51 to 7.76.

Artificial lead sulphide may be prepared in the dry way, or by precipitating a lead salt solution with hydrogen sulphide or other soluble sulphide.

When iead is heated in sulphur vapour the metal burns and forms crystals or fused globules of the sulphide. The sulphide is also formed when lead oxide is heated with excess of sulphur. The formation of lead sulphide by the action of atmospheric hydrogen sulphide on lead pigments is well known; it accounts for the darkening of oil-paintings by age, and of structures coated with paint into the composition of which white lead enters. On this account no part of a chemical laboratory should be covered with lead paint. Further, it is frequently observed that powders containing lead compounds darken after exposure for a short time to the air of a laboratory in which hydrogen sulphide is being employed.

When lead sulphide is precipitated by hydrogen sulphide from a solution of lead acetate or nitrate the precipitate is amorphous, but when it is formed in a dilute solution containing free nitric acid, it is obtained crystallised in microscopic cubes.

Whilst crystallised lead sulphide is dark grey the precipitated sulphide is brownish black. The two forms differ in density; the density of the crystallised compound is 7.48 and of the amorphous 7.13. The melting-point of lead sulphide lies in the region of 1000° C.; that of galena has been estimated to be 1120° C.; the sulphide, however, sublimes below its melting-point, and a sublimate has been observed in a vacuum as low as 600° C., consisting of cubes which may be 1.5 mm. in diameter. On account of this property crystals of sublimed galena are often obtained in lead works. The molecular heat of formation of precipitated lead sulphide is 20,400 or 20,300 calories; its specific heat, which varies somewhat with temperature, has a mean value of about 0.068.

Lead sulphide is reduced to metal when heated in a current of hydrogen; chlorine converts it into chloride with the simultaneous formation of sulphur dichloride, SCl2, but in presence of water-vapour forms the peroxide. Dilute nitric acid dissolves lead sulphide with the formation of nitrate in solution and separation of sulphur. At the same time some of this sulphur is oxidised to sulphuric acid with the consequent formation of lead sulphate; and this is specially the case when the concentrated acid is employed, so that the sulphide appears to be directly oxidised to sulphate. Hot concentrated hydrochloric acid dissolves lead sulphide with evolution of hydrogen sulphide; and this sulphide is by no means insoluble in the dilute acid, so that traces of lead may remain in solution after the passage of hydrogen sulphide if too much hydrochloric acid was present, and in the course of qualitative analysis will subsequently be precipitated as hydroxide by ammonia. Several other sulphides are less soluble in water than lead sulphide, e.g. cupric and silver sulphides. Consequently double decomposition occurs when freshly precipitated lead sulphide is shaken with solutions of cupric or silver salts. The solubility in water of precipitated lead sulphide at 18° C. is 3.60×10-6 gram-molecules per litre; that of the crystallised sulphide is about a third this value. When lead sulphide is fused with caustic soda in the air, the sulphide is oxidised to sulphate, which dissolves in the soda. This is an example of the influence of a solvent upon oxidation, since the reaction depends upon the solubility of lead sulphate in caustic soda; it is analogous to the oxidation of manganese and chromic compounds to manganate and chromate under the same conditions. Similarly, precipitated lead sulphide is oxidised and dissolved when it is boiled with sodium peroxide and water.


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