Lead dioxide
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| Names | |
|---|---|
| IUPAC names
Lead dioxide
Lead(IV) oxide | |
| Other names
Plumbic oxide
Plattnerite | |
| Identifiers | |
| ECHA InfoCard | 100.013.795 |
| RTECS number |
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| UN number | 1872 |
CompTox Dashboard (EPA)
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| Properties | |
| PbO2 | |
| Molar mass | 239.2 g/mol |
| Appearance | black powder |
| Density | 9.38 g/cm3 |
| Melting point | 290 ºC decomp. |
| insoluble | |
| Hazards | |
| Flash point | Non-flammable |
| Related compounds | |
Other cations
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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).
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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
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