Lead(II) chromate

Last updated
Lead(II) chromate
PbCrO4.jpg
   Lead, Pb
   Chromium, Cr
   Oxygen, O
C.I.77600.jpg
Names
Other names
see text
Identifiers
ChEBI
ECHA InfoCard 100.028.951 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 231-846-0
PubChem CID
RTECS number
  • GB2975000
UNII
UN number 3288
Properties
PbCrO4
Molar mass 323.192 g/mol
Appearanceorange-yellow powder
Density 6.12 g/cm3, solid
Melting point 844 °C (1,551 °F; 1,117 K)
negligible
Solubility soluble in diluted nitric acid
insoluble in acetic acid, ammonia
−18.0·10−6 cm3/mol
2.31
Structure
monoclinic
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
Carcinogen and highly toxic
GHS labelling:
GHS-pictogram-skull.svg GHS-pictogram-silhouette.svg GHS-pictogram-pollu.svg
Danger
H350, H360, H373, H410
P201, P273, P308+P313, P501
NFPA 704 (fire diamond)
NFPA 704.svgHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
3
0
0
Lethal dose or concentration (LD, LC):
>12 g/kg (mouse, oral)
Safety data sheet (SDS) ICSC 0003
Sigma-Aldrich
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(II) chromate is an inorganic compound with the chemical formula Pb Cr O 4. It has a vivid yellow color and is generally insoluble. Two polymorphs of lead chromate are known, orthorhombic and the more stable monoclinic form. Monoclinic lead chromate is used in paints under the name chrome yellow, and many other names. [1] It occurs also as the mineral crocoite.

Contents

Structure

Lead chromate adopts the monazite structure, meaning that the connectivity of the atoms is very similar to other compounds of the type MM'O4. Pb(II) has a distorted coordination sphere being surrounded by eight oxides with Pb-O distances ranging from 2.53 to 2.80 Å. The chromate anion is tetrahedral, as usual. [2] Unstable polymorphs of lead chromate are the greenish yellow orthorhombic form and a red-orange tetragonal form. [1]

Applications

Lead chromate is used as the bright yellow pigment in Sunflowers, a painting by Vincent van Gogh. Vincent van Gogh - Sunflowers - VGM F458.jpg
Lead chromate is used as the bright yellow pigment in Sunflowers , a painting by Vincent van Gogh.

Approximately 37,000 tons were produced in 1996. The main applications are as a pigment in paints, under the name chrome yellow. [5]

Preparation

Lead(II) chromate can be produced by treating sodium chromate with lead salts such as lead(II) nitrate or by combining lead(II) oxide with chromic acid.

Related lead sulfochromate pigments are produced by the replacement of some chromate by sulfate, resulting in a mixed lead-chromate-sulfate compositions Pb(CrO4)1−x(SO4)x. This replacement is possible because sulfate and chromate are isostructural. Since sulfate is colorless, sulfochromates with high values of x are less intensely colored than lead chromate. [5] In some cases, chromate is replaced by molybdate. [1]

Reactions

Heating in hydroxide solution produces chrome red, a red or orange powder made by PbO and CrO3. Also, in hydroxide solution lead chromate slowly dissolves forming plumbite complex.

PbCrO4 + 4 OH− → [Pb(OH)4]2− + CrO2−4

Safety hazards

Despite containing both lead and hexavalent chromium, lead chromate is not particularly toxic because of its very low solubility. The LD50 for rats is only 5,000 mg/kg. Lead chromate is treated with great care in its manufacture, the main concerns being dust of the chromate precursor. "Extensive epidemiological investigations have given no indication that the practically insoluble lead chromate pigments have any carcinogenic properties". [5] Despite its low acute toxicity and lack of broad evidence for carcinogenicity, lead chromate is highly regulated in advanced countries. One of the greatest threats comes from inhalation of particles, so much effort has been devoted to production of low-dust forms of the pigment. [1]

In the 1800s, the product was used to impart a bright yellow color to some types of candy. [6] It is used (illegally) to enhance the color of certain spices, particularly turmeric, [7] [8] particularly in Bangladesh. [9] [10]

Unlike other lead-based paint pigments, lead chromate is still widely used.

See also

Related Research Articles

<span class="mw-page-title-main">Chromium</span> Chemical element, symbol Cr and atomic number 24

Chromium is a chemical element; it has symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal.

In chemistry, a salt is a chemical compound consisting of an ionic assembly of positively charged cations and negatively charged anions, which results in a compound with no net electric charge. A common example is table salt, with positively charged sodium ions and negatively charged chloride ions.

<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.

Chromic acid is jargon for a solution of formed by the addition of sulfuric acid to aqueous solutions of dichromate. It consists at least in part of chromium trioxide.

<span class="mw-page-title-main">Chromate and dichromate</span> Chromium(VI) anions

Chromate salts contain the chromate anion, CrO2−
4. Dichromate salts contain the dichromate anion, Cr
2O2−
7. They are oxyanions of chromium in the +6 oxidation state and are moderately strong oxidizing agents. In an aqueous solution, chromate and dichromate ions can be interconvertible.

<span class="mw-page-title-main">Barium chloride</span> Chemical compound

Barium chloride is an inorganic compound with the formula BaCl2. It is one of the most common water-soluble salts of barium. Like most other water-soluble barium salts, it is a white powder, highly toxic, and imparts a yellow-green coloration to a flame. It is also hygroscopic, converting to the dihydrate BaCl2·2H2O, which are colourless crystals with a bitter salty taste. It has limited use in the laboratory and industry.

<span class="mw-page-title-main">Potassium dichromate</span> Chemical compound

Potassium dichromate, K2Cr2O7, is a common inorganic chemical reagent, most commonly used as an oxidizing agent in various laboratory and industrial applications. As with all hexavalent chromium compounds, it is acutely and chronically harmful to health. It is a crystalline ionic solid with a very bright, red-orange color. The salt is popular in laboratories because it is not deliquescent, in contrast to the more industrially relevant salt sodium dichromate.

<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.

Chrome yellow is a bright, warm yellow pigment that has been used in art, fashion, and industry. It is the premier orange pigment for many applications.

<span class="mw-page-title-main">Crocoite</span> Lead chromate mineral

Crocoite is a mineral consisting of lead chromate, PbCrO4, and crystallizing in the monoclinic crystal system. It is identical in composition with the artificial product chrome yellow used as a paint pigment.

<span class="mw-page-title-main">Potassium chromate</span> Chemical compound

Potassium chromate is the inorganic compound with the formula K2CrO4. This yellow solid is the potassium salt of the chromate anion. It is a common laboratory chemical, whereas sodium chromate is important industrially.

<span class="mw-page-title-main">Silver chromate</span> Chemical compound

Silver chromate is an inorganic compound with formula Ag2CrO4 which appears as distinctively coloured brown-red crystals. The compound is insoluble and its precipitation is indicative of the reaction between soluble chromate and silver precursor salts (commonly potassium/sodium chromate with silver nitrate). This reaction is important for two uses in the laboratory: in analytical chemistry it constitutes the basis for the Mohr method of argentometry, whereas in neuroscience it is used in the Golgi method of staining neurons for microscopy.

<span class="mw-page-title-main">Caesium chromate</span> Chemical compound

Caesium chromate or cesium chromate is an inorganic compound with the formula Cs2CrO4. It is a yellow crystalline solid that is the caesium salt of chromic acid, and it crystallises in the orthorhombic system.

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

Zinc chromate, ZnCrO4, is a chemical compound, a salt containing the chromate anion, appearing as odorless yellow powder or yellow-green crystals, but, when used for coatings, pigments are often added. It is used industrially in chromate conversion coatings, having been developed by the Ford Motor Company in the 1920s.

<span class="mw-page-title-main">Barium chromate</span> Chemical compound

Barium chromate, is a yellow sand like powder with the formula BaCrO4. It is a known oxidizing agent and produces a green flame when heated, a result of the barium ions.

<span class="mw-page-title-main">Chrome orange</span> Chemical compound and inorganic pigment

Chrome orange is a mixed oxide with the chemical formula Pb2CrO5. It can be made by treating a lead(II) salt with an alkaline solution of a chromate or by treating chrome yellow (PbCrO4) with strongly basic solution.

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

Sodium chromate is the inorganic compound with the formula Na2CrO4. It exists as a yellow hygroscopic solid, which can form tetra-, hexa-, and decahydrates. It is an intermediate in the extraction of chromium from its ores.

References

  1. 1 2 3 4 Erkens, LJH; Hamers, H.; Hermans, RJM; Claeys, E.; Bijnens, M. (2001). "Lead chromates: A Review of the State of the Art in 2000". Surface Coatings International Part B: Coatings Transactions. 84 (3): 169–176. doi:10.1007/BF02700395. S2CID   94606296.
  2. ↑ Quareni, S.; de Pieri, R. "A three-dimensional refinement of the structure of crocoite, PbCrO4" Acta Crystallographica 1965, volume 19, p287-p289. doi : 10.1107/S0365110X65003304
  3. ↑ "Sunflowers - Van Gogh Museum". vangoghmuseum.nl. Archived from the original on 29 October 2016. Retrieved 21 September 2016.
  4. ↑ Monico, Letizia; Janssens, Koen; Hendriks, Ella; Vanmeert, Frederik; Van Der Snickt, Geert; Cotte, Marine; Falkenberg, Gerald; Brunetti, Brunetto Giovanni; Miliani, Costanza (2015). "Evidence for Degradation of the Chrome Yellows in Van Gogh's Sunflowers: A Study Using Noninvasive In Situ Methods and Synchrotron-Radiation-Based X-ray Techniques". Angewandte Chemie International Edition. 54 (47): 13923–13927. doi:10.1002/anie.201505840. PMID   26482035. S2CID   2268072.
  5. 1 2 3 Völz, Hans G.; et al. (2006). "Pigments, Inorganic". Ullmann's Encyclopedia of Industrial Chemistry . Weinheim: Wiley-VCH. doi:10.1002/14356007.a20_243.pub2. ISBN   978-3527306732.
  6. ↑ Wisconsin. State Board of Health (1887). Progress Report of Public Health in Wisconsin, Volume 10. p. 92. Retrieved 17 July 2013. (Google Books)
  7. ↑ "The American Spice Trade Association's Statement on Lead in Turmeric - ASTA: The Voice of the U.S. Spice Industry in the Global Market". ASTA: The Voice of the U.S. Spice Industry in the Global Market. 28 October 2013. Retrieved 21 November 2018.
  8. ↑ Angelon-Gaetz, Kim A.; Klaus, Christen; Chaudhry, Ezan A.; Bean, Deidre K. (23 November 2018). "Lead in Spices, Herbal Remedies, and Ceremonial Powders Sampled from Home Investigations for Children with Elevated Blood Lead Levels — North Carolina, 2011–2018". MMWR. Morbidity and Mortality Weekly Report. 67 (46): 1290–1294. doi:10.15585/mmwr.mm6746a2. ISSN   0149-2195. PMC   6289082 . PMID   30462630.
  9. ↑ "Researchers find lead in turmeric". Phys. Stanford University. 24 September 2019. Retrieved 1 October 2019.
  10. ↑ Forsyth, Jenna E.; Nurunnahar, Syeda; Islam, Sheikh Shariful; Baker, Musa; Yeasmin, Dalia; Islam, M. Saiful; Rahman, Mahbubur; Fendorf, Scott; Ardoin, Nicole M.; Winch, Peter J.; Luby, Stephen P. (December 2019). "Turmeric means "yellow" in Bengali: Lead chromate pigments added to turmeric threaten public health across Bangladesh". Environmental Research. 179 (Pt A): 108722. Bibcode:2019ER....179j8722F. doi: 10.1016/j.envres.2019.108722 . PMID   31550596.
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