Zinc potassium chromate

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Structural formula
No drawing available
General
Surname Zinc potassium chromate
other names

Potassium hydroxyoctaoxodizincate dichromate

Molecular formula KZn 2 (CrO 2 ) 2 (H 2 O) (OH)
Brief description

greenish-yellow, odorless solid

External identifiers / databases
CAS number 11103-86-9
EC number 234-329-8
ECHA InfoCard 100.031.196
PubChem 25466
Wikidata Q62086578
properties
Molar mass 418.85 g mol −1
Physical state

firmly

solubility

<1 mg / ml in water at 20 ° C

safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary
09 - Dangerous for the environment 08 - Dangerous to health 07 - Warning

danger

H and P phrases H: 302-317-350-410
P: ?
Authorization procedure under REACH

of particular concern : carcinogenic ( CMR ); subject to approval

As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Zinc potassium chromate is the chemical compound of the pigment zinc yellow from the group of inorganic chromates . The empirical formula of the pigment was than KZn 2 (CrO 2 ) 2 (H 2 O) (OH) is determined, that as a hydroxide - hydrate of Zinkkaliumchromats, but it is also the crystal water -free form KZn 2 (CrO 4 ) 2 (OH ) specified. The pigment has been known since the beginning of the 19th century .

The other chromates of zinc are also sometimes referred to as zinc yellow, namely zinc chromate with the formula ZnCrO 4 , basic zinc potassium chromate with the formula K 2 Zn 4 (CrO 4 ) 4 (OH) 2 and tetrahydroxozinc chromate or zinc chromate hydroxide with the formula Zn 5 (CrO 4 ) (OH) 8 as they have similar color and chemical properties.

properties

Zinc potassium chromate crystallizes in the same crystal structure as natrochalcite . In the monoclinic crystal system in the space group C 2 / m (space group no. 12) there are two formula units per unit cell . The zinc ions are octahedrally coordinated by oxygen ions and form corner-linked chains. These are in turn linked by tetrahedral chromate groups to form layers in which the potassium ions are also located. Between the layers lie water and hydroxide molecules that hold these layers together through hydrogen bonds . Since there is a strong hydrogen bond between H 2 O and OH - and the molecules come very close, they were described together (as with natrochalcite) as an H 3 O 2 - unit. Template: room group / 12

The zinc yellow pigment is subject to aging , which changes its color. A famous example is the work A Sunday afternoon on the island of La Grande Jatte by Georges Seurat , where the artist used the fairly new pigment. Significant changes in color to brown were observed less than five years after the work was completed. Scientific studies have shown that the influence of light and air humidity can lead to a change in the oxidation state from chromium (VI) to Cr (III), but also to the formation of dichromate and thus to discoloration. Due to the popularity of the work, efforts were also made to recreate the original color strength of the picture through computer simulation .

safety

Like most chromates, zinc potassium chromate is considered to be carcinogenic and its use is no longer permitted in the EEA .

Individual evidence

  1. ↑ a b c Kim Pilkjær Simonsen, Marie Bitsch Christiansen, Morten Gotthold Vinum, Jana Sanyova, Jesper Bendix: Single crystal X-ray structure of the artists' pigment zinc yellow. In: Journal of Molecular Structure. 1141, 2017, p. 322, doi : 10.1016 / j.molstruc . 2017.03.108 .
  2. ↑ a b c https://cameochemicals.noaa.gov/chemical/9204
  3. ↑ Template: CL Inventory / harmonized Harmonized classification and labeling of zinc chromates including zinc potassium chromate in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on June 11, 2019.
  4. ↑ Not explicitly listed in Regulation (EC) No. 1272/2008 (CLP) , but with the specified labeling falls under the group entry zinc chromates including zinc potassium chromate in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on June 11 2019. Manufacturers or distributors can expand the harmonized classification and labeling .
  5. ↑ Entry in the SVHC list of the European Chemicals Agency , accessed on March 5, 2019.
  6. ↑ a b Entry in the list of substances subject to authorization of the European Chemicals Agency , accessed on March 5, 2019.
  7. ↑ Entry on potassium hydroxyoctaoxodizincate dichromate in the GESTIS substance database of the IFA , accessed on June 7, 2019(JavaScript required) .
  8. ↑ Vanessa Otero, Marta F. Campos, Joana V. Pinto, Márcia Vilarigues, Leslie Carlyle, Maria João Melo: Barium, zinc and strontium yellows in late 19th – early 20th century oil paintings. In: Heritage Science. 5, 2017, doi : 10.1186 / s40494-017-0160-3 .
  9. ↑ Entry on zinc chromate in the GESTIS substance database of the IFA , accessed on June 7, 2019(JavaScript required) .
  10. ↑ Entry on zinc potassium chromate, basic in the GESTIS substance database of the IFA , accessed on June 7, 2019(JavaScript required) .
  11. ↑ Entry on zinc chromate hydroxide in the GESTIS substance database of the IFA , accessed on June 7, 2019(JavaScript required) .
  12. ↑ a b F. Casadio, S. Xie, SC Rukes, B. Myers, KA Gray, R. Warta, I. Fiedler: Electron energy loss spectroscopy elucidates the elusive darkening of zinc potassium chromate in Georges Seurat's A Sunday on La La Grande Jatte -1884. In: Analytical and Bioanalytical Chemistry. 399, 2011, p. 2909, doi : 10.1007 / s00216-010-4264-9 .
  13. ↑ Luciana Zanella, Francesca Casadio, Kimberly A. Gray, Richard Warta, Qing Ma, Jean-François Gaillard: The darkening of zinc yellow: XANES speciation of chromium in artist's paints after light and chemical exposures. In: Journal of Analytical Atomic Spectrometry. 26, 2011, p. 1090, doi : 10.1039 / C0JA00151A .
  14. ^ Roy S. Berns, Siobhan Byrns, Francesca Casadio, Inge Fiedler, Christopher Gallagher, Francisco H. Imai, Alan Newman, Lawrence A. Taplin: Rejuvenating the color palette of Georges Seurat'sA Sunday on La Grande Jatte — 1884: A simulation . In: Color Research & Application. 31, 2006, p. 278, doi : 10.1002 / col.20223 .
  15. ↑ Berns, RS Rejuvenating Seurat's palette Using Color and Imaging Science: A simulation, site of RS Berns at Rochester Institute of Technology