Lead dioxide

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Lead dioxide
IUPAC name	lead(IV) oxide
Other names	plumbic oxide
Identifiers
CAS number	[1309-60-0]
Properties
Molecular formula	PbO2
Molar mass	239.2 g/mol
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Lead(IV) oxide, PbO₂, also plumbic oxide and lead dioxide, 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

[edit] External links

• National Pollutant Inventory: Lead and Lead Compounds Fact Sheet