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Lead(II) nitrate

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Template:Chembox new Lead(II) nitrate is a chemical compound, the inorganic salt of nitric acid and lead, with the formula Pb(NO3)2. It is a colourless crystal or white powder and a strong, stable oxidizer. Unlike most other lead(II) salts, it is soluble in water. Its main use from the Middle Ages, under the name plumbum dulce, has been as raw material in the production of many pigments. Since the 20th century, it has been industrially used as a heat stabilizer in nylon and polyesters, and in coatings of photothermographic paper. Commercial production did not take place until the 19th century in Europe, and in the United States until after 1943, with a typical production process of metallic lead or lead oxide in nitric acid.

Lead(II) nitrate is toxic and probably carcinogenic to humans. Therefore, it is to be handled and stored with the appropriate safety precautions.

History

Since the Middle Ages, lead(II) nitrate has been produced on a very small scale as a raw material for the production of coloured pigments, such as chrome yellow (lead(II) chromate), chrome orange (lead(II) hydroxide chromate) and similar lead compounds. As early as the 15th century, the German alchemist Andreas Libavius synthesized the compound, coining the medieval names of plumb dulcis and calx plumb dulcis.[1] Although the production process is chemically straightforward, production was minimal until the 19th century, and no non-European production before the 20th century is reported.[2][3]

Chemistry

When lead(II) nitrate is heated, it decomposes to lead(II) oxide, accompanied by a crackling noise referred to as decrepitation. Because of this property, lead nitrate is sometimes used in pyrotechnics such as fireworks.

2 Pb(NO3)2(s) → 2 PbO(s) + 4 NO2(g) + O2(g)

Aqueous chemistry

Lead(II) nitrate readily dissolves in water to give a clear colourless solution.[4] This solution reacts with soluble iodides such as potassium iodide to produce a precipitate of the bright orange-yellow lead(II) iodide. This reaction is often used to demonstrate precipitation, because of the striking colour change observed. It also takes place in solid phase, when solid lead nitrate and potassium iodide are finely ground and mixed in a mortar.

Pb(NO3)2(aq) + 2KI(aq) → PbI2(s) + 2 KNO3(aq)

Apart from lead(II) nitrate, lead(II) acetate is the only other common soluble lead compound. All other lead compounds are insoluble in water, even when coupled with commonly very soluble anions such as chloride, bromide and iodide. Lead(II) chloride, lead(II) bromide and lead(II) iodide, (collectively known as lead halides), are only soluble in hot water approaching boiling. This means that lead(II) nitrate has particular importance as a starting point for the production of insoluble lead compounds via double decomposition. Incidentally, hot solutions of lead halides can be brought to precipitation on cooling to create feathery, iridescent crystals suspended in water, the colour of which crystal is dependent on the particular halide (chloride = white, bromide = buff, iodide = yellow). These crystals appear suddenly, when the solutions dip below the recrystallization temperature, and can be extremely beautiful to observe.

When 1 M sodium hydroxide solution is added to 0.1 M lead nitrate, basic nitrates are formed, even well past the equivalence point. Up through the half equivalence point, Pb(NO3)2·Pb(OH)2 predominates, then after this point Pb(NO3)2·5Pb(OH)2 is formed. Surprisingly, no simple Pb(OH)2 is formed up to at least pH 12.[5]

Crystal structure

Crystal structure [111] plane

The crystal structure of solid lead(II) nitrate has been determined by neutron diffraction.[6] The compound crystallizes in the cubic system with the lead atoms in a face-centered cubic system. Its space group is Pa3 (Bravais lattice notation) with each side of the cube with length 784 picometers.

The black dots represent the lead atoms, while the white dots represent the nitrate groups 27 pm above the plane of the lead atoms, and the blue dots represent the nitrate groups the same distance below this plane. In this configuration every lead atom is bonded to 12 oxygen atoms (bond length: 281 pm). All N-O bond lengths are identical: 125 pm.

Academic interest in the crystal structure of this compound was partly based on the possibility of free internal rotation of the nitrate groups within the crystal lattice at elevated temperatures, but this did not materialise.[7]

Complexation

Lead(II) nitrate has some interesting supramolecular chemistry associated with it because of its coordination to nitrogen and oxygen electron donating compounds. The interest is largely academic but with some potential applications. For example, combining lead nitrate and pentaethylene glycol in a solution of acetonitrile and methanol followed by slow evaporation produces a new crystalline material [Pb(NO3)2(EO5)].[8] The crystal structure for this compound has the PEO chain wrapped around the lead ion in an equatorial plane similar to a crown ether. The two bidentate nitrate ligands are situated in a trans configuration. The total coordination number is 10 with the lead ion in a bicapped square antiprism molecular geometry.

The complex formed by lead(II) nitrate, lead(II) perchlorate and a bithiazole bidentate N-donor ligand[9] is binuclear with a nitrate group forming a bridge between the lead atoms with coordination number of 5 and 6. One interesting aspect of this type of complexes is the presence of a physical gap in the coordination sphere (i.e., the ligands are not placed symmetrically around the metal ion), and it is suggested that this is due to a lead lone pair of electrons. The same phenomenon is described in lead complexes with an imidazole ligand.[10]

This type of chemistry is not always unique to lead nitrate; other lead(II) compounds such as lead(II) bromide also form complexes, but the nitrate is frequently used because of its solubility properties and its bidentate nature.

Preparation

The compound is normally obtained by dissolving lead as the metal or oxide in aqueous nitric acid.[11] Anhydrous Pb(NO3)2 can be crystallised directly from the solution. There is no known industrial scale production.

3 Pb + 8 HNO3 → 3 Pb(NO3)2 + 2 NO + 4H2O
PbO + 2 HNO3 → Pb(NO3)2 + H2O

Applications

Historically lead(II) nitrate is used in the manufacture of matches and special explosives such as lead azide, in mordants and pigments (e.g., in lead paints), for dyeing and printing calico and other textiles, and in the general manufacture of lead compounds. More recent applications include use as a heat stabilizer in nylon and polyesters, as a coating for photothermograpic paper, and in rodenticides.

Lead(II) nitrate also provides a reliable source of pure dinitrogen tetroxide in the laboratory. When the salt is carefully dried, and heated in a steel vessel, it produces nitrogen dioxide along with dioxygen. The gases are condensed and fractionally distilled to give pure N2O4.[12]

2 Pb(NO3)2(s) → 2 PbO(s) + 4 NO2(g) + O2(g)
2 NO2 ⇌ N2O4

Safety

The hazards of lead(II) nitrate are those of soluble lead compounds in general and, to a lesser extent, those of other inorganic nitrates. It is toxic, and ingestion may lead to acute lead poisoning. Symptoms include intestinal malfunction, strong abdominal pains, appetite loss, nausea, vomiting and cramps, while longer-term exposure may lead to neurological and renal problems. Lead compounds are known to be cumulative poisons, as more than 90% of absorbed lead is fixed in bone tissue from which it is only slowly released over a period of years.

Children are more efficient at absorbing lead from the gastrointestinal tract than adults, and thus more at risk from lead poisoning. Exposure to lead compounds during pregnancy has been linked to increased rates of spontaneous abortion, fetal malformation and low birth weight. Given the cumulative nature of lead toxicity, children and pregnant women should be exposed to soluble lead compounds as little as possible — this is a legal requirement in many countries.[13]

Inorganic lead compounds are classified by the International Agency for Research on Cancer (IARC) as probably carcinogenic to humans (Category 2A). They have been linked to renal cancer and glioma in experimental animals and to renal cancer, brain cancer and lung cancer in humans, although studies of workers exposured to lead are often complicated by a concurrent exposure to arsenic.[14] Lead is known to substitute for zinc in a number of enzymes, including δ-aminolevulinic acid dehydratase (porphobilinogen synthase) in the heme biosynthetic pathway and pyrimidine-5′-nucleotidase, important for the correct metabolism of DNA.

Due care should be taken before and during handling of lead(II) nitrate, including the use of protective equipment such as eye and face protection and rubber gloves. Experiments with lead(II) nitrate should be conducted in fume hoods, and spillages must not be discharged into the environment (details in the material safety data sheets, as listed under external links).

See also

References

  1. ^ "Pigment through the ages". WebExhibits. Retrieved 2006-10-11.
  2. ^ "Lead". Encyclopædia Britannica Eleventh Edition. Retrieved 2006-10-11.
  3. ^ Libavius, Andreas (1595). Alchemia Andreæ Libavii. Francofurti.
  4. ^ Ferris, L.M. (1959). "Lead nitrate—Nitric acid—Water system" (PDF). Journal of Chemicals and Engineering Date. Oak Ridge National Laboratory. Retrieved 2006-10-11. {{cite journal}}: Unknown parameter |month= ignored (help)
  5. ^ Pauley, J. L. (1954). "Basic Salts of Lead Nitrate Formed in Aqueous Media". Journal of the American Chemical Society: pp4220–4222. {{cite journal}}: |pages= has extra text (help); Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |vol= ignored (|volume= suggested) (help)
  6. ^ Hamilton, W.C. (1957). "A neutron crystallographic study of lead nitrate". Acta Cryst. 10: 103–107. doi:10.1107/S0365110X57000304.
  7. ^ Nowotny, H. (1986). "Structure refinement of lead nitrate" (pdf). Acta Cryst. C42: p133–135. doi:10.1107/S0108270186097032. {{cite journal}}: |pages= has extra text (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  8. ^ Rogers, Robin D. (1996). "Structural Chemistry of Poly (ethylene glycol). Complexes of Lead(II) Nitrate and Lead(II) Bromide". Inorg. Chem.: pp6964–6973. doi:10.1021/ic960587b. {{cite journal}}: |pages= has extra text (help); Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |vol= ignored (|volume= suggested) (help)
  9. ^ Mahjoub, Ali Reza (2001). "A Dimeric Mixed-Anions Lead(II) Complex: Synthesis and Structural Characterization of [Pb2(BTZ)4(NO3)(H2O)](ClO4)3 {BTZ = 4,4'-Bithiazole}". Chemistry Letters. 30(12): 1234. doi:10.1246/cl.2001.1234. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  10. ^ Wan, Shuang-Yi (2002). "2D 4.8² Network with threefold parallel interpenetration from nanometer-sized tripodal ligand and lead(II) nitrate". Chem. Commun.: 2520–2521. doi:10.1039/b207568g. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  11. ^ Adlam, G.H.J. (1945). Higher School Certificate Inorganic Chemistry. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  12. ^ Greenwood, N.N. (1997). Chemistry of the Elements (2nd edition ed.). Oxford: Butterworth-Heinemann. pp. p456. ISBN 0-7506-3365-4. {{cite book}}: |edition= has extra text (help); |pages= has extra text (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  13. ^ e.g. France: Art. R234-20, Code du travail.
  14. ^ Monographs on the Evaluation of Carcinogenic Risks to Humans: Inorganic and organic lead compounds. Vol. 87. IARC. 2004-02-10. Retrieved 2006-11-02. {{cite book}}: Check date values in: |date= (help)
Material Safety Data Sheets

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