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Lead(II) chromate

Lead(II) chromate

2291 insoluble in acetic acid, ammonia Sigma-Aldrich | NFPA-H = 3 | NFPA-R = 0 | NFPA-F = 0

Lead(II) chromate is an inorganic compound with the chemical formula . It is a bright yellow salt that is very poorly soluble in water. It occurs also as the mineral crocoite. It is used as a pigment (chrome yellow).

Structure

Structure of PbCrO4 as determined by [[X-ray crystallography]]. Color code: red = O, dark gray = Pb, light gray = Cr.

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. Lead chromate adopts the monazite structure, meaning that the connectivity of the atoms is very similar to other compounds of the type . 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. Unstable polymorphs of lead chromate are the greenish yellow orthorhombic form and a red-orange tetragonal form.

Applications

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

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 . 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. In some cases, chromate is replaced by molybdate.

Reactions

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

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Safety hazards

Despite containing both lead and hexavalent chromium, lead chromate is not acutely lethal because of its very low solubility. The LD50 for rats is only 5,000 mg/kg. Lead chromate must be treated with great care in its manufacture, the main concerns being dust of the chromate precursor. Lead chromate is highly regulated in advanced countries. As one of the greatest threats comes from inhalation of particles, much effort has been devoted to production of low-dust forms of the pigment.

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

Unlike other lead-based paint pigments, lead chromate is still widely used, especially in road marking paint.

In 2023 and 2024, consumption of adulterated cinnamon led to at least 136 cases of lead toxicity in children in the United States as reported by the US Centers for Disease Control and Prevention. The affected products were recalled. The US Food and Drug Administration determined that the ratio of lead to chromium in the cinnamon indicated that lead chromate had been added to the cinnamon.

References

References

  1. {{RubberBible87th
  2. (2001). "Lead chromates: A Review of the State of the Art in 2000". Surface Coatings International Part B: Coatings Transactions.
  3. 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
  4. "Sunflowers - Van Gogh Museum".
  5. (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.
  6. Völz, Hans G.. (2006). "Pigments, Inorganic".
  7. Wisconsin. State Board of Health. (1887). "Progress Report of Public Health in Wisconsin, Volume 10".
  8. (28 October 2013). "The American Spice Trade Association's Statement on Lead in Turmeric - ASTA: The Voice of the U.S. Spice Industry in the Global Market".
  9. (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.
  10. (24 September 2019). "Researchers find lead in turmeric". Phys.
  11. (December 2019). "Turmeric means "yellow" in Bengali: Lead chromate pigments added to turmeric threaten public health across Bangladesh". Environmental Research.
  12. "Lead Chromate: Why it is Banned in Most Industries Apart From Road Markings". Verdict Media Limited.
  13. (15 August 2024). "Investigation of Elevated Lead & Chromium Levels: Cinnamon Applesauce Pouches (November 2023)".
  14. (17 April 2024). "Lead and Chromium Poisoning Outbreak Linked to Cinnamon Applesauce Pouches".
Wikipedia Source

This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page.

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