litharge

Lead(II) oxide
IUPAC name	Lead(II) oxide
Other names	Lead monoxide Litharge Massicot Plumbous oxide
Identifiers
CAS number	1317-36-8 Y
UN number	3288
RTECS number	OG1750000
Properties
Molecular formula	PbO
Molar mass	223.20 g/mol
Appearance	red or yellow solid
Density	9.64 g/cm3 [1]
Melting point	888 °C
Boiling point	1477 °C
Solubility in water	insoluble
Solubility	insoluble in alkalis soluble in HCl
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
Flash point	Non-flammable
Related compounds
Other anions	Lead sulfide Lead selenide Lead telluride
Other cations	Carbon monoxide Silicon monoxide Germanium(II) oxide Tin(II) oxide
Related lead oxides	Lead(II,IV) oxide Lead dioxide
Related compounds	Thallium(III) oxide Bismuth(III) oxide
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Lead(II) oxide is the inorganic compound with the formula PbO. Lead(II) oxide occurs in two polymorphs, red, having a tetragonal crystal structure and yellow, having an orthorhombic crystal structure. Both forms occur naturally as the rare minerals: the red form is known as litharge and the yellow form is known as massicot.^[2]

Preparation and structure

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:^[3]

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

As determined by X-ray crystallography, the compound features pyramidal four-coordinate Pb center. The pyramidal nature indicates the presence of a stereo-chemically active lone pair of electrons.^[4]

Reactions

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:^[2] PbO + H₂O + OH^- → [Pb(OH)₃]^-

Applications

PbO is produced on a large scale as an intermediate in the conversion of lead ores, mainly galena into metallic lead. The consumption of lead, and hence the processing of PbO, correlates with the number of automobiles because it remains the key component of automotive batteries.^[5]

PbO is used extensively in manufacturing of lead glasses and ceramic glazes as well as in fine dinnerware. For such applications, the PbO is converted in situ to lead silicate, which is less toxic. Other less dominating applications in the vulcanization of rubber and to produce certain pigments and paints.^[6] 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]}

Niche or declining uses

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 aquaria, and was also once used to seal glass panels in window frames. It is a component of lead paints.

PbO is used in certain condensation reactions in organic synthesis.^[7]

Health issues

Lead oxide is toxic and affects reproduction and development. It can bioaccumulate in plants and in mammals.^[8]

References

1. ^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0070494398
2. ^ ^{a b} Holleman, A. F.; Wiberg, E. (2001), Inorganic Chemistry, San Diego: Academic Press, ISBN 0-12-352651-5 
3. ^ N.N. Greenwood, A. Earnshaw, "Chemistry of Elements", 2nd edition, Butterworth-Heinemann, 1997.
4. ^ Wells, A. F. (1984), Structural Inorganic Chemistry (5th ed.), Oxford: Clarendon Press, ISBN 0-19-855370-6 
5. ^ 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
6. ^ Dodd S. Carr "Lead Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, Weinhiem. doi:10.1002/14356007.a15_249
7. ^ Corson, B. B. (1936), "1,4-Diphenylbutadiene", Org. Synth. 16: 28, http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV2P0229 ; Coll. Vol. 2: 229 
8. ^ "Lead (II) oxide". International Occupational Safety and Health Information Centre. http://www.ilo.org/safework_bookshelf/english?d&nd=857171610. Retrieved 2009-06-06. 

External links

• Case Studies in Environmental Medicine - Lead Toxicity
• ToxFAQs: Lead
• National Pollutant Inventory - Lead and Lead Compounds Fact Sheet
• Webelements PbO