Chromium(III) hydroxide explained

Chromium(III) hydroxide is a gelatinous green inorganic compound with the chemical formula . It is a polymer with an undefined structure and low solubility. It is amphoteric, dissolving in both strong alkalis and strong acids.^[1]

In alkali: Cr(OH)3 + OH- -> CrO2- + 2 H2O

In acid: Cr(OH)3(OH2)3 + 3 H+ -> Cr(OH2)6^3+

It is used as a pigment, as a mordant, and as a catalyst for organic reactions.^[2]

It is manufactured by adding a solution of ammonium hydroxide to a solution of chromium salt.

Pure is as yet (2020) unknown among the mineral species. However, three natural polymorphs of the oxyhydroxide, CrO(OH), are known: bracewellite, grimaldiite and guyanaite.^{[3] [4] [5] [6]}

Notes and References

1. Rai, Dhanpat; Sass, Bruce M.; Moore, Dean A. "Chromium(III) hydrolysis constants and solubility of chromium(III) hydroxide" Inorganic Chemistry 1987, volume 26, pp. 345-9.
2. Book: Holleman, Arnold F.. Walter de Gruyter. 1985. 91–100. 1081–1095. 3-11-007511-3. Lehrbuch der Anorganischen Chemie. Wiberg, Egon . Wiberg, Nils. Chromium. German.
3. Web site: Bracewellite.
4. Web site: Grimaldiite.
5. Web site: Guyanaite.
6. Web site: List of Minerals. 21 March 2011.