Lead(II) oxide

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Lead(II) oxide
Oxid olovnatý.JPG
PbO structure.png
Identifiers
CAS number 1317-36-8 YesY
PubChem 14827
UN number 3288
RTECS number OG1750000
Properties
Molecular formula PbO
Molar mass 223.20 g/mol
Appearance red or yellow powder
Density 9.53 g/cm3
Melting point 888 °C (1,630 °F; 1,161 K)
Boiling point 1,477 °C (2,691 °F; 1,750 K)
Solubility in water 0.00504 g/100 mL (alpha form)
0.01065 g/100 mL (beta form)
Solubility insoluble in dilute alkalis, alcohol
soluble in concentrated alkalis
soluble in HCl, ammonium chloride
Structure
Crystal structure tetragonal, tP4
Space group P4/nmm, No. 129
Hazards
MSDS ICSC 0288
EU Index 082-001-00-6
EU classification Repr. Cat. 1/3
Harmful (Xn)
Dangerous for the environment (N)
R-phrases R61, R20/22, R33, R62, R50/53
S-phrases S53, S45, S60, S61
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point Non-flammable
Related compounds
Other anions Lead sulfide
Lead selenide
Lead telluride
Other cations Carbon monoxide
Silicon monoxide
Tin(II) oxide
Related lead oxides Lead(II,II,IV) oxide
Lead dioxide
Related compounds Thallium(III) oxide
Bismuth(III) oxide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Lead(II) oxide, also called lead monoxide, is the inorganic compound with the molecular formula PbO. PbO occurs in two polymorphs, one litharge having a tetragonal crystal structure and the other massicot having an orthorhombic crystal structure. Modern applications for PbO are mostly in lead-based industrial glass and industrial ceramics, including computer components.

Preparation[edit]

PbO may be prepared by heating lead metal in air at approx. 600 °C. At this temperature it is also the end product of oxidation of other lead oxides in air:[1]

PbO2 –(293 °C)→ Pb12O19 –(351 °C)→ Pb12O17 –(375 °C)→ Pb3O4 –(605 °C)→ PbO

Thermal decomposition of lead(II) nitrate or lead carbonate also results in the PbO formation:

2 Pb(NO3)2 → 2 PbO + 4 NO2 + O2
PbCO3 → PbO + CO2

PbO is produced on a large scale as an intermediate product in refining raw lead ores into metallic lead. The usual lead ore is galena (lead(II) sulfide). At high temperature (1000 °C) the sulfide is converted to the oxide:[2]

2 PbS + 3 O2 → 2PbO + 2SO2

Metallic lead is obtained by reducing the PbO with carbon monoxide at around 1200 °C:.[3]

PbO + CO → Pb + CO2

Structure[edit]

As determined by X-ray crystallography, both polymorphs, tetragonal and orthorhombic feature a pyramidal four-coordinate Pb center. In the tetragonal form the four Pb-O bonds have the same length, but in the orthorhombic two are shorter and two longer. The pyramidal nature indicates the presence of a stereo-chemically active lone pair of electrons.[4] When PbO occurs in tetragonal lattice structure it is called litharge; and when the PbO has orthorhombic lattice structure it is called massicot. The PbO can be changed from massicot to litharge or vice versa by controlled heating and cooling.[5] The tetragonal form is usually red or orange color, while the orthorhombic is usually yellow or orange, but the color is not a very reliable indicator of the structure.[6] The tetragonal and orthorhombic forms of PbO occur naturally as rare minerals.

Reactions[edit]

The red and yellow forms of this material are related by a small change in enthalpy: PbO(red) → PbO(yellow) ΔH = 1.6 kJ/mol

PbO is amphoteric, which means that it reacts with both acids and with bases. With acids, it forms salts of Pb2+ via the intermediacy of oxo clusters such as [Pb6O(OH)6]4+. With strong base, PbO dissolves to form plumbite(II) salts:[7] PbO + H2O + OH- → [Pb(OH)3]-

Applications[edit]

The kind of lead in lead glass in normally PbO, and PbO is used extensively in making glass. Depending on the glass, the benefit of using PbO in glass can be one or more of (1) increasing the refractive index of the glass, (2) decreasing the viscosity of the glass, (3) increasing the electrical resistivity of the glass, and (4) increasing the ability of the glass to absorb X-rays. Adding PbO to industrial ceramics (as well as glass) makes the materials more magnetically and electrically inert (raises the Curie temperature) and is often used for this purpose.[8] Historically PbO was also used extensively in ceramic glazes for household ceramics, and it is still used, but not extensively any more. Other less dominating applications include the vulcanization of rubber and the production of certain pigments and paints.[9] PbO is used in cathode ray tube glass to block X-ray emission, but mainly in the neck and funnel because it can cause discoloration when used in the faceplate. Strontium oxide is preferred for the faceplate.[citation needed]

The consumption of lead, and hence the processing of PbO, correlates with the number of automobiles because it remains the key component of automotive lead-acid batteries.[10]

Niche or declining uses[edit]

A mixture of PbO with glycerine sets to a hard, waterproof cement that has been used to join the flat glass sides and bottoms of aquariums, and was also once used to seal glass panels in window frames. It is a component of lead paints.

In powdered tetragonal litharge form, it can be mixed with linseed oil and then boiled to create a weather-resistant sizing used in gilding. The litharge would give the sizing a dark red color that made the gold leaf appear warm and lustrous, while the linseed oil would impart adhesion and a flat durable binding surface.

PbO is used in certain condensation reactions in organic synthesis.[11]

Alchemy[edit]

Lead oxide played a central role in alchemy as the reaction turned lead into a yellow material believed to be gold falsely indicating a successful transformation of base metals into gold.[citation needed]

Health issues[edit]

Main article: Lead poisoning
PbOlabel.jpg

Lead oxide may be fatal if swallowed or inhaled. It causes irritation to skin, eyes, and respiratory tract. It affects gum tissue, central nervous system, kidneys, blood, and reproductive system. It can bioaccumulate in plants and in mammals.[12]

References[edit]

  1. ^ N.N. Greenwood, A. Earnshaw, "Chemistry of Elements", 2nd edition, Butterworth-Heinemann, 1997.
  2. ^ Abdel-Rehim, A. M. (2006), "Thermal and XRD analysis of Egyptian galena", Journal of Thermal Analysis and Calorimetry 86 (2): 393–401 
  3. ^ Lead Processing @ Universalium.academic.ru. Alt address: Lead processing @ Enwiki.net.
  4. ^ Wells, A. F. (1984), Structural Inorganic Chemistry (5th ed.), Oxford: Clarendon Press, ISBN 0-19-855370-6 
  5. ^ A simple example is given in A Text Book of Inorganic Chemistry, by Anil Kumar De, year 2007, page 383. A more complex example is in The Chemistry of Metal Alkoxides, published by Kluwer Academic Publishers, year 2002, section 9.4 on lead alkoxides, page 115.
  6. ^ Lead manufacturing in Britain, by David John Rowe, year 1983, page 16.
  7. ^ Holleman, A. F.; Wiberg, E. (2001), Inorganic Chemistry, San Diego: Academic Press, ISBN 0-12-352651-5 
  8. ^ Chapter 9, "Lead Compounds", in the book Ceramic and Glass Materials: Structure, Properties and Processing, published by Springer, year 2008.
  9. ^ Dodd S. Carr "Lead Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, Weinhiem. doi:10.1002/14356007.a15_249
  10. ^ Charles A. Sutherland, Edward F. Milner, Robert C. Kerby, Herbert Teindl, Albert Melin, Hermann M. Bolt “Lead” in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. doi:10.1002/14356007.a15_193.pub2
  11. ^ Corson, B. B. (1936), "1,4-Diphenylbutadiene", Org. Synth. 16: 28 ; Coll. Vol. 2: 229 
  12. ^ "Lead (II) oxide". International Occupational Safety and Health Information Centre. Retrieved 2009-06-06. 

External links[edit]