Potassium hypochromate

Potassium hypochromate

Names
Other names Potassium chromate(V)
Identifiers
3D model (JSmol)	Interactive image
SMILES O=[Cr-3](=O)(=O)=O.[K+].[K+].[K+]
Properties
Chemical formula	K3CrO4
Molar mass	233.2886 g/mol
Appearance	Green solid
Melting point	1,000 °C (1,830 °F; 1,270 K) (decomposes)
Solubility in water	Soluble, decomposes (25 °C) [1]
Structure
Crystal structure	Similar to potassium hypomanganate
Thermochemistry
Std enthalpy of formation (ΔfH⦵298)	−370 ± 2 kcal mol−1 [2]
Hazards
Flash point	Not flammable
Related compounds
Other anions	Potassium hypomanganate
Other cations	Sodium hypochromate
Related chromates	Potassium chromate Potassium perchromate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Potassium hypochromate is a chemical compound with the formula K₃CrO₄ with the unusual Cr⁵⁺ ion. This compound is unstable in water but stable in alkaline solution ^[1] and was found to have a similar crystal structure to potassium hypomanganate. ^[2]

Preparation

This compound is commonly prepared by reacting chromium(III) oxide and potassium hydroxide at 850 °C under argon: ^[2]

Cr₂O₃ + 6 KOH → 2 K₃CrO₄ + H₂O + 2 H₂

This compound can be prepared other ways such as replacing chromium oxide with potassium chromate. It is important that there is no Fe²⁺ ions present because it would reduce the Cr(V) ions to Cr(III) ions. ^[1]

Reactions

Potassium hypochromate decomposes in water to form chromium(III) oxide and potassium chromate when alkali is not present or low. ^[1] Potassium hypochromate also reacts with acids such as hydrochloric acid to form chromium(III) oxide, potassium chromate, and potassium chloride: ^[2]

6 K₃CrO₄ + 10 HCl → 4 K₂CrO₄ + Cr₂O₃ + 5 H₂O + 10 KCl

Other reducing agents such as hydroperoxides can oxidize the hypochromate ion into chromate ions. ^[1] At extremely high temperatures, it decomposes into potassium chromate and potassium metal. ^[2]

This compound is used to synthesize various compounds such as chromyl chlorosulfate by reacting this compound with chlorosulfuric acid. ^[3]

References

1. N. Bailey; M. C. R. Symons (1957). "Structure and reactivity of the oxyanions of transition metals. Part III. The hypochromate ion". Journal of the Chemical Society (Resumed). 35: 203–207. doi:10.1039/jr9570000203.
2. Lawrence H. Johnson; Loren G. Hepler; Carlos E. Bamberger; Donald M. Richardson (1978). "The enthalpy of formation of potassium chromate(V), K₃CrO₄(c)". Canadian Journal of Chemistry. 56 (4). The Ohio State University: National Research Council: 446–449. doi: 10.1139/v78-071 .
3. Silvia A. Brandán (2012). "1". A Structural and Vibrational Study of the Chromyl Chlorosulfate, Fluorosulfate, and Nitrate Compounds (Ebook). Springer Netherlands. p. 2. ISBN   9789400757639 . Retrieved 15 October 2021.