Lead dioxide

Lead dioxide

Names
IUPAC names Lead dioxide Lead(IV) oxide
Other names Plumbic oxide Plattnerite
Identifiers
CAS Number	1309-60-0 N
ECHA InfoCard	100.013.795
RTECS number	OGO700000
UN number	1872
CompTox Dashboard (EPA)	DTXSID5025497
Properties
Chemical formula	PbO2
Molar mass	239.2 g/mol
Appearance	black powder
Density	9.38 g/cm3
Melting point	290 ºC decomp.
Solubility in water	insoluble
Hazards
Flash point	Non-flammable
Related compounds
Other cations	Carbon dioxide Silicon dioxide Germanium dioxide Tin dioxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Lead dioxide, PbO₂, also plumbic oxide and lead(IV) oxide, is an oxide of lead, with lead in oxidation state +4. It has a molar mass of 239.2 g/mol. It occurs in nature as the mineral plattnerite.

When hydrated, it forms plumbic hydroxide or lead(IV) hydroxide, Pb(OH)₄; given the formula, this is a mainly hypothetical compound.

Lead dioxide is amphoteric. Lead dioxide can dissolve in strong base to form plumbate ion, Pb(OH)₆²⁻. This can then form plumbate compounds. In acid conditions, it is typically reduced to lead(II) ion, Pb²⁺; lead(IV) ion, Pb⁴⁺, is not found in aqueous solution.

The most important use of lead dioxide is as the cathode of lead acid batteries. This arises from the anomalous metallic conductivity of PbO₂—TiO₂, ZrO₂, GeO₂, and SnO₂ are all insulators with a band gap around 3eV, however PbO₂ is a metallic conductor. This is thought to be due to anionic vacancies in the structure creating a formally mixed valent lead oxidation state.

A lead acid battery is based on the equilibrium between lead metal and lead dioxide in sulfuric acid.

Pb + PbO₂ + 2HSO₄⁻ + 2H⁺ → 2PbSO₄ + 2H₂O, E = +2.05 V

External links

• National Pollutant Inventory: Lead and Lead Compounds Fact Sheet