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. ^ a b c d e 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. ^ a b c d e 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.