Lead dioxide

Last updated
Lead dioxide
Lead dioxide.jpg
Oxid olovicity.PNG
Names
IUPAC name
Lead(IV) oxide
Other names
Plumbic oxide
Plattnerite
Identifiers
ChemSpider
ECHA InfoCard 100.013.795 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 215-174-5
PubChem CID
RTECS number
  • OGO700000
UNII
UN number 1872
Properties
PbO2
Molar mass 239.1988 g/mol
Appearancedark-brown, black powder
Density 9.38 g/cm3
Melting point 290 °C (554 °F; 563 K) decomposes
insoluble
Solubility soluble in acetic acid
insoluble in alcohol
2.3
Structure
hexagonal
Hazards
GHS labelling:
GHS-pictogram-rondflam.svg GHS-pictogram-exclam.svg GHS-pictogram-silhouette.svg GHS-pictogram-pollu.svg
Danger
H272, H302, H332, H360, H372, H373, H410
P201, P202, P210, P220, P221, P260, P261, P264, P270, P271, P273, P280, P281, P301+P312, P304+P312, P304+P340, P308+P313, P312, P314, P330, P370+P378, P391, P405, P501
NFPA 704 (fire diamond)
NFPA 704.svgHealth 4: Very short exposure could cause death or major residual injury. E.g. VX gasFlammability 0: Will not burn. E.g. waterInstability 3: Capable of detonation or explosive decomposition but requires a strong initiating source, must be heated under confinement before initiation, reacts explosively with water, or will detonate if severely shocked. E.g. hydrogen peroxideSpecial hazard OX: Oxidizer. E.g. potassium perchlorate
4
0
3
OX
Flash point Non-flammable
Safety data sheet (SDS) External MSDS
Related compounds
Other cations
Carbon dioxide
Silicon dioxide
Germanium dioxide
Tin dioxide
Related lead oxides
Lead(II) oxide
Lead(II,IV) oxide
Related compounds
 Thallium(III) oxide
Bismuth(III) oxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)

Lead(IV) oxide, commonly known as lead dioxide, is an inorganic compound with the chemical formula PbO2. It is an oxide where lead is in an oxidation state of +4. [1] It is a dark-brown solid which is insoluble in water. [2] It exists in two crystalline forms. It has several important applications in electrochemistry, in particular as the positive plate of lead acid batteries.

Contents

Properties

Physical

Crystal structure of a- PbO2 ScrutinyiteStructure.png
Crystal structure of α-PbO2
Crystal structure of b- PbO2 PlattneriteStructure.png
Crystal structure of β-PbO2

Lead dioxide has two major polymorphs, alpha and beta, which occur naturally as rare minerals scrutinyite and plattnerite, respectively. Whereas the beta form had been identified in 1845, [3] α-PbO2 was first identified in 1946 and found as a naturally occurring mineral 1988. [4]

The alpha form has orthorhombic symmetry, space group Pbcn (No. 60), Pearson symbol oP12, lattice constants a = 0.497 nm, b = 0.596 nm, c = 0.544 nm, Z = 4 (four formula units per unit cell). [4] The lead atoms are six-coordinate.

The symmetry of the beta form is tetragonal, space group P42/mnm (No. 136), Pearson symbol tP6, lattice constants a = 0.491 nm, c = 0.3385 nm, Z = 2 [5] and related to the rutile structure and can be envisaged as containing columns of octahedra sharing opposite edges and joined to other chains by corners. This contrasts with the alpha form where the octahedra are linked by adjacent edges to give zigzag chains. [4]

Chemical

Lead dioxide decomposes upon heating in air as follows:

24 PbO2 → 2 Pb12O19 + 5 O2
Pb12O19 → Pb12O17 + O2
2 Pb12O17 → 8 Pb3O4 + O2
2 Pb3O4 → 6 PbO + O2

The stoichiometry of the end product can be controlled by changing the temperature – for example, in the above reaction, the first step occurs at 290 °C, second at 350 °C, third at 375 °C and fourth at 600 °C. In addition, Pb2O3 can be obtained by decomposing PbO2 at 580–620 °C under an oxygen pressure of 1,400 atm (140 MPa). Therefore, thermal decomposition of lead dioxide is a common way of producing various lead oxides. [6]

Lead dioxide is an amphoteric compound with prevalent acidic properties. It dissolves in strong bases to form the hydroxyplumbate ion, [Pb(OH)6]2−: [2]

PbO2 + 2 NaOH + 2 H2O → Na2[Pb(OH)6]

It also reacts with basic oxides in the melt, yielding orthoplumbates M4[PbO4].

Because of the instability of its Pb4+ cation, lead dioxide reacts with hot acids, converting to the more stable Pb2+ state and liberating oxygen: [6]

2 PbO2 + 2 H2SO4 → 2 PbSO4 + 2 H2O + O2
2 PbO2 + 4 HNO3 → 2 Pb(NO3)2 + 2 H2O + O2
PbO2 + 4 HCl → PbCl2 + 2 H2O + Cl2

However these reactions are slow.

Lead dioxide is well known for being a good oxidizing agent, with an example reactions listed below: [7]

2 MnSO4 + 5 PbO2 + 6 HNO3 → 2 HMnO4 + 2 PbSO4 + 3 Pb(NO3)2 + 2 H2O
2 Cr(OH)3 + 10 KOH + 3 PbO2 → 2 K2CrO4 + 3 K2 PbO2 + 8 H2O

Electrochemical

Although the formula of lead dioxide is nominally given as PbO2, the actual oxygen to lead ratio varies between 1.90 and 1.98 depending on the preparation method. Deficiency of oxygen (or excess of lead) results in the characteristic metallic conductivity of lead dioxide, with a resistivity as low as 10−4 Ω·cm and which is exploited in various electrochemical applications. Like metals, lead dioxide has a characteristic electrode potential, and in electrolytes it can be polarized both anodically and cathodically. Lead dioxide electrodes have a dual action, that is both the lead and oxygen ions take part in the electrochemical reactions. [8]

Production

Chemical processes

Lead dioxide is produced commercially by several methods, which include oxidation of red lead (Pb3O4) in alkaline slurry in a chlorine atmosphere, [6] reaction of lead(II) acetate with "chloride of lime" (calcium hypochlorite), [9] [10] The reaction of Pb3O4 with nitric acid also affords the dioxide: [2] [11]

Pb3O4 + 4 HNO3 → PbO2 + 2 Pb(NO3)2 + 2 H2O

PbO2 reacts with sodium hydroxide to form the hexahydroxoplumbate(IV) ion [Pb(OH)6]2−, soluble in water.

Electrolysis

An alternative synthesis method is electrochemical: lead dioxide forms on pure lead, in dilute sulfuric acid, when polarized anodically at electrode potential about +1.5 V at room temperature. This procedure is used for large-scale industrial production of PbO2 anodes. Lead and copper electrodes are immersed in sulfuric acid flowing at a rate of 5–10 L/min. The electrodeposition is carried out galvanostatically, by applying a current of about 100 A/m2 for about 30 minutes.

The drawback of this method for the production of lead dioxide anodes is its softness, especially compared to the hard and brittle PbO2 which has a Mohs hardness of 5.5. [12] This mismatch in mechanical properties results in peeling of the coating which is preferred for bulk PbO2 production. Therefore, an alternative method is to use harder substrates, such as titanium, niobium, tantalum or graphite and deposit PbO2 onto them from lead(II) nitrate in static or flowing nitric acid. The substrate is usually sand-blasted before the deposition to remove surface oxide and contamination and to increase the surface roughness and adhesion of the coating. [13]

Applications

Lead dioxide is used in the production of matches, pyrotechnics, dyes and the curing of sulfide polymers. It is also used in the construction of high-voltage lightning arresters. [6]

Lead dioxide is used as an anode material in electrochemistry. β-PbO2 is more attractive for this purpose than the α form because it has relatively low resistivity, good corrosion resistance even in low-pH medium, and a high overvoltage for the evolution of oxygen in sulfuric- and nitric-acid-based electrolytes. Lead dioxide can also withstand chlorine evolution in hydrochloric acid. Lead dioxide anodes are inexpensive and were once used instead of conventional platinum and graphite electrodes for regenerating potassium dichromate. They were also applied as oxygen anodes for electroplating copper and zinc in sulfate baths. In organic synthesis, lead dioxide anodes were applied for the production of glyoxylic acid from oxalic acid in a sulfuric acid electrolyte. [13]

Lead acid battery

The most important use of lead dioxide is as the cathode of lead acid batteries. Its utility arises from the anomalous metallic conductivity of PbO2. The lead acid battery stores and releases energy by shifting the equilibrium (a comproportionation) between metallic lead, lead dioxide, and lead(II) salts in sulfuric acid.

Pb + PbO2 + 2 HSO−4 + 2 H+ → 2 PbSO4 + 2 H2O E° = +2.05 V

Safety

Lead compounds are poisons. Chronic contact with the skin can potentially cause lead poisoning through absorption, or redness and irritation in the short term. [14]

PbO2 is not combustible, but it enhances flammability of other substances and the intensity of the fire. In case of a fire it gives off irritating and toxic fumes. [15] [ better source needed ]

Lead dioxide is poisonous to aquatic life, but because of its insolubility it usually settles out of water. [16] [15]

Related Research Articles

<span class="mw-page-title-main">Electrochemistry</span> Branch of chemistry

Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference and identifiable chemical change. These reactions involve electrons moving via an electronically-conducting phase between electrodes separated by an ionically conducting and electronically insulating electrolyte.

<span class="mw-page-title-main">Nitric acid</span> Highly corrosive mineral acid

Nitric acid is an inorganic compound with the formula HNO3. It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into oxides of nitrogen. Most commercially available nitric acid has a concentration of 68% in water. When the solution contains more than 86% HNO3, it is referred to as fuming nitric acid. Depending on the amount of nitrogen dioxide present, fuming nitric acid is further characterized as red fuming nitric acid at concentrations above 86%, or white fuming nitric acid at concentrations above 95%.

<span class="mw-page-title-main">Sulfuric acid</span> Chemical compound (H₂SO₄)

Sulfuric acid or sulphuric acid, known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, and hydrogen, with the molecular formula H2SO4. It is a colorless, odorless, and viscous liquid that is miscible with water.

<span class="mw-page-title-main">Electrolysis</span> Technique in chemistry and manufacturing

In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from naturally occurring sources such as ores using an electrolytic cell. The voltage that is needed for electrolysis to occur is called the decomposition potential. The word "lysis" means to separate or break, so in terms, electrolysis would mean "breakdown via electricity."

In chemistry, a half reaction is either the oxidation or reduction reaction component of a redox reaction. A half reaction is obtained by considering the change in oxidation states of individual substances involved in the redox reaction. Often, the concept of half reactions is used to describe what occurs in an electrochemical cell, such as a Galvanic cell battery. Half reactions can be written to describe both the metal undergoing oxidation and the metal undergoing reduction.

<span class="mw-page-title-main">Redox</span> Chemical reaction in which oxidation states of atoms are changed

Redox is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a decrease in the oxidation state. The oxidation and reduction processes occur simultaneously in the chemical reaction.

<span class="mw-page-title-main">Oxidizing agent</span> Chemical compound used to oxidize another substance in a chemical reaction

An oxidizing agent is a substance in a redox chemical reaction that gains or "accepts"/"receives" an electron from a reducing agent. In other words, an oxidizer is any substance that oxidizes another substance. The oxidation state, which describes the degree of loss of electrons, of the oxidizer decreases while that of the reductant increases; this is expressed by saying that oxidizers "undergo reduction" and "are reduced" while reducers "undergo oxidation" and "are oxidized". Common oxidizing agents are oxygen, hydrogen peroxide, and the halogens.

<span class="mw-page-title-main">Nitric oxide</span> Colorless gas with the formula NO

Nitric oxide is a colorless gas with the formula NO. It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its chemical formula. Nitric oxide is also a heteronuclear diatomic molecule, a class of molecules whose study spawned early modern theories of chemical bonding.

<span class="mw-page-title-main">Lead(II) nitrate</span> Chemical compound

Lead(II) nitrate is an inorganic compound with the chemical formula Pb(NO3)2. It commonly occurs as a colourless crystal or white powder and, unlike most other lead(II) salts, is soluble in water.

<span class="mw-page-title-main">Nitrogen dioxide</span> Chemical compound with formula NO₂

Nitrogen dioxide is a chemical compound with the formula NO2. One of several nitrogen oxides, nitrogen dioxide is a reddish-brown gas. It is a paramagnetic, bent molecule with C2v point group symmetry. Industrially, NO2 is an intermediate in the synthesis of nitric acid, millions of tons of which are produced each year, primarily for the production of fertilizers.

An acidic oxide is an oxide that either produces an acidic solution upon addition to water, or acts as an acceptor of hydroxide ions effectively functioning as a Lewis acid. Acidic oxides will typically have a low pKa and may be inorganic or organic. A commonly encountered acidic oxide, carbon dioxide produces an acidic solution when dissolved.

<span class="mw-page-title-main">Copper(II) oxide</span> Chemical compound – an oxide of copper with formula CuO

Copper(II) oxide or cupric oxide is an inorganic compound with the formula CuO. A black solid, it is one of the two stable oxides of copper, the other being Cu2O or copper(I) oxide (cuprous oxide). As a mineral, it is known as tenorite, or sometimes black copper. It is a product of copper mining and the precursor to many other copper-containing products and chemical compounds.

The lead chamber process was an industrial method used to produce sulfuric acid in large quantities. It has been largely supplanted by the contact process.

<span class="mw-page-title-main">Lead(II,IV) oxide</span> Chemical compound

Lead(II,IV) oxide, also called red lead or minium, is the inorganic compound with the formula Pb3O4. A bright red or orange solid, it is used as pigment, in the manufacture of batteries, and rustproof primer paints. It is an example of a mixed valence compound, being composed of both Pb(II) and Pb(IV) in the ratio of two to one.

<span class="mw-page-title-main">Sodium periodate</span> Chemical compound

Sodium periodate is an inorganic salt, composed of a sodium cation and the periodate anion. It may also be regarded as the sodium salt of periodic acid. Like many periodates, it can exist in two different forms: sodium metaperiodate (formula‍ NaIO4) and sodium orthoperiodate (normally Na2H3IO6, but sometimes the fully reacted salt Na5IO6). Both salts are useful oxidising agents.

<span class="mw-page-title-main">Zinc nitrate</span> Chemical compound

Zinc nitrate is an inorganic chemical compound with the formula Zn(NO3)2. This colorless, crystalline salt is highly deliquescent. It is typically encountered as a hexahydrate Zn(NO3)2·6H2O. It is soluble in both water and alcohol.

<span class="mw-page-title-main">Birkeland–Eyde process</span> Nitrogen fixation process using electrical arcs

The Birkeland–Eyde process was one of the competing industrial processes in the beginning of nitrogen-based fertilizer production. It is a multi-step nitrogen fixation reaction that uses electrical arcs to react atmospheric nitrogen (N2) with oxygen (O2), ultimately producing nitric acid (HNO3) with water. The resultant nitric acid was then used as a source of nitrate (NO3−) in the reaction which may take place in the presence of water or another proton acceptor.

<span class="mw-page-title-main">Lead compounds</span> Type of compound

Compounds of lead exist with lead in two main oxidation states: +2 and +4. The former is more common. Inorganic lead(IV) compounds are typically strong oxidants or exist only in highly acidic solutions.

<span class="mw-page-title-main">Polonium dioxide</span> Chemical compound

Polonium dioxide (also known as polonium(IV) oxide) is a chemical compound with the formula PoO2. It is one of three oxides of polonium, the other two being polonium monoxide (PoO) and polonium trioxide (PoO3). It is a pale yellow crystalline solid at room temperature. Under lowered pressure (such as a vacuum), it decomposes into elemental polonium and oxygen at 500 °C. It is the most stable oxide of polonium and is an interchalcogen.

References

  1. ↑ Meek, Terry L.; Garner, Leah D. (2005-02-01). "Electronegativity and the Bond Triangle". Journal of Chemical Education. 82 (2): 325. Bibcode:2005JChEd..82..325M. doi:10.1021/ed082p325. ISSN   0021-9584.
  2. 1 2 3 Eagleson, Mary (1994). Concise Encyclopedia of Chemistry. Walter de Gruyter. p. 590. ISBN   978-3-11-011451-5.
  3. ↑ Haidinger, W. (1845). "Zweite Klasse: Geogenide. II. Ordnung. Baryte VII. Bleibaryt. Plattnerit.". Handbuch der Bestimmenden Mineralogie (PDF) (in German). Vienna: Braumüller & Seidel. p. 500.
  4. 1 2 3 Taggard, J. E. Jr.; et al. (1988). "Scrutinyite, natural occurrence of α-PbO2 from Bingham, New Mexico, U.S.A., and Mapimi, Mexico" (PDF). Canadian Mineralogist. 26: 905.
  5. ↑ Harada, H.; Sasa, Y.; Uda, M. (1981). "Crystal data for β-PbO2" (PDF). Journal of Applied Crystallography. 14 (2): 141. doi:10.1107/S0021889881008959.
  6. 1 2 3 4 Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 386. ISBN   978-0-08-037941-8.
  7. ↑ Kumar De, Anil (2007). A Textbook of Inorganic Chemistry. New Age International. p. 387. ISBN   978-81-224-1384-7.
  8. ↑ Barak, M. (1980). Electrochemical power sources: primary and secondary batteries. IET. pp. 184 ff. ISBN   978-0-906048-26-9.
  9. ↑ M. Baulder (1963). "Lead(IV) Oxide". In G. Brauer (ed.). Handbook of Preparative Inorganic Chemistry, 2nd Ed. Vol. 1. NY, NY: Academic Press. p. 758.
  10. ↑ Wiberg, Nils (2007). Lehrbuch der Anorganischen Chemie[Textbook of Inorganic chemistry] (in German). Berlin: de Gruyter. p. 919. ISBN   978-3-11-017770-1.
  11. ↑ Sutcliffe, Arthur (1930). Practical Chemistry for Advanced Students (1949 ed.). London: John Murray.
  12. ↑ "Plattnerite: Plattnerite mineral information and data". www.mindat.org. Retrieved 12 April 2018.
  13. 1 2 François Cardarelli (2008). Materials Handbook: A Concise Desktop Reference. Springer. p. 574. ISBN   978-1-84628-668-1.
  14. ↑ "LEAD DIOXIDE". hazard.com. Archived from the original on 13 April 2021. Retrieved 12 April 2018.{{cite web}}: CS1 maint: unfit URL (link)
  15. 1 2 PubChem. "Lead dioxide". pubchem.ncbi.nlm.nih.gov. Retrieved 2022-12-15.
  16. ↑ "Product and Company Identification" (PDF). ltschem.com. Retrieved 29 February 2024.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.