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]
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| Names | |
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Other names
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| Identifiers | |
3D model (JSmol)
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| Properties | |
| K3CrO4 | |
| Molar mass | 233.2886 g/mol |
| Appearance | Green solid |
| Melting point | 1,000 °C (1,830 °F; 1,270 K) (decomposes) |
| Soluble, decomposes (25 °C)[1] | |
| 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
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Potassium hypomanganate |
Other cations
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Sodium hypochromate |
Related chromates
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Potassium chromate Potassium perchromate |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Preparation
editThis 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
editPotassium 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
edit- ^ 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.
- ^ 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.
- ^ 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.