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Compounds of lead exist with lead in two main oxidation states: +2 and +4. The former is more common. Inorganic lead(IV) compounds are typically strong or exist only in highly acidic solutions.
Metallic lead is attacked (oxidized) only superficially by air, forming a thin layer of lead oxide that protects it from further oxidation. The metal is not attacked by sulfuric acid or hydrochloric acids. It dissolves in nitric acid with the evolution of nitric oxide gas to form dissolved Pb(NO3)2.
When heated with of alkali metals, metallic lead oxidizes to form PbO (also known as litharge), leaving the corresponding alkali nitrite. PbO is representative of lead's +2 oxidation state. It is soluble in nitric and acetic acid acids, from which solutions it is possible to precipitate halide, lead sulfate, lead chromate, lead carbonate (PbCO3), and basic carbonate ( salts of lead. The lead sulfide can also be precipitated from lead acetate solutions. These salts are all poorly soluble in water. Among the halides, the iodide is less soluble than the bromide, which, in turn, is less soluble than the chloride. (1996). 9780471135579, John Wiley and Sons. ISBN 9780471135579
Lead(II) oxide is also soluble in alkali metal hydroxide solutions to form the corresponding plumbite salt.
halogenation of plumbite solutions causes the formation of lead's +4 oxidation state.
Lead dioxide is representative of the +4 oxidation state, and is a powerful oxidizing agent. The chloride of this oxidation state is formed only with difficulty and decomposes readily into lead(II) chloride and chlorine gas. The bromide and iodide of lead(IV) are not known to exist. Lead dioxide dissolves in alkali hydroxide solutions to form the corresponding .
Lead also has an oxide with mixed +2 and +4 oxidation states, lead tetroxide (), also known as minium.
Lead readily forms an equimolar alloy with sodium metal that reacts with to form organometallic compounds of lead such as tetraethyllead.
The dioxide may be prepared by, for example, halogenization of lead(II) salts. The alpha allotrope is rhombohedral, and the beta allotrope is tetragonal. Both allotropes are black-brown in color and always contain some water, which cannot be removed, as heating also causes decomposition (to PbO and Pb3O4). The dioxide is a powerful oxidizer: it can oxidize hydrochloric and sulfuric acids. It does not reacts with alkaline solution, but reacts with solid alkalis to give hydroxyplumbates, or with basic oxides to give plumbates.
Reaction of lead with sulfur or hydrogen sulfide yields lead sulfide. The solid has the NaCl-like structure (simple cubic), which it keeps up to the melting point, 1114 °C (2037 °F). If the heating occurs in presence of air, the compounds decomposes to give the monoxide and the sulfate. The compounds are almost insoluble in water, weak acids, and (NH4)2S/(NH4)2S2 solution is the key for separation of lead from analytical groups I to III elements, tin, arsenic, and antimony. The compounds dissolve in nitric and hydrochloric acids, to give elemental sulfur and hydrogen sulfide, respectively. Heating mixtures of the monoxide and the sulfide forms the metal.
Other dihalides are received upon heating lead(II) salts with the halides of other metals; lead dihalides precipitate to give white orthorhombic crystals (diiodide form yellow hexagonal crystals). They can also be obtained by direct elements reaction at temperature exceeding melting points of dihalides. Their solubility increases with temperature; adding more halides first decreases the solubility, but then increases due to complexation, with the maximum coordination number being 6. The complexation depends on halide ion numbers, atomic number of the alkali metal, the halide of which is added, temperature and solution ionic strength. The tetrachloride is obtained upon dissolving the dioxide in hydrochloric acid; to prevent the exothermic decomposition, it is kept under concentrated sulfuric acid. The tetrabromide may not, and the tetraiodide definitely does not exist. The diastatide has also been prepared. (1989). 9780471186564, John Wiley & Sons. ISBN 9780471186564
The metal is not attacked by sulfuric acid or hydrochloric acids. It dissolves in nitric acid with the evolution of nitric oxide gas to form dissolved Pb(NO3)2. It is a well-soluble solid in water; it is thus a key to receive the precipitates of halide, lead sulfate, lead chromate, lead carbonate, and basic carbonate Pb3(OH)2(CO3)2 salts of lead.
| + Equilibrium constants for aqueous lead chloride complexes at 25 °C (2025). 9781566704625, CRC Press. ISBN 9781566704625 | |
| Pb2+ + Cl− → PbCl+ | K1 = 12.59 |
| PbCl+ + Cl− → PbCl2 | K2 = 14.45 |
| PbCl2 + Cl− → | K3 = 0.398 |
| + Cl− → | K4 = 0.0892 |
Lead readily forms an equimolar alloy with sodium metal that reacts with to form organometallic compounds of lead such as tetraethyllead. The Pb–C bond energies in TML and TEL are only 167 and 145 kJ/mol; the compounds thus decompose upon heating, with first signs of TEL composition seen at 100 °C (210 °F). Pyrolysis yields elemental lead and alkyl radicals; their interreaction causes the synthesis of HEDL. They also decompose upon sunlight or UV-light. In presence of chlorine, the alkyls begin to be replaced with chlorides; the R2PbCl2 in the presence of HCl (a by-product of the previous reaction) leads to the complete mineralization to give PbCl2. Reaction with bromine follows the same principle.
| Plot showing aqueous concentration of dissolved Pb2+ as a function of | Diagram for lead in sulfate media |
The addition of chloride can lower the solubility of lead, though in chloride-rich media (such as aqua regia) the lead can become soluble again as anionic chloro complexes.
| Diagram showing the solubility of lead in chloride media. The lead concentrations are plotted as a function of the total chloride present. | Pourbaix diagram for lead in chloride (0.1 M) media |
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