Preparation of chromium(III) hydroxide
Twenty-five grams of potassium dichromate (or 17g of chromium(VI) oxide) are dissolved in 500ml of water. Sulfur dioxide is bubbled into the solution until reduction to the trivalent state is complete, as indicated by the pure green color of the liquid with no trace of yellow. The solution is then boiled to remove excess sulfur dioxide. Alternatively, the reduction may be carried out by adding the chromium(VI) compound to a mixture of 420ml of water and 80ml of concentrated hydrochloric acid and then adding 35ml of ethyl alcohol. The reduced solution is boiled as directed to remove excess alcohol and acetaldehyde (oxidation product). The solution of chromic salt is heated to boiling and stirred continuously while concentrated ammonia water is added slowly from a tap funnel or burette. About 40ml are required to give a slight excess of the reagent. Avoid adding too much ammonia because chromium tends to form complex ammines. The precipitated chromium(III) hydroxide is suction filtered on a large Buchner funnel, washed thoroughly with three 100ml portions of boiling water and dried in the desiccator.
Inorganic laboratory preparations, by G. G. Schlessinger, 82, 1962
Chromic hydroxide, Chromic oxide gel, CHROMIUM TRIHYDROXIDE, Chromic oxide, hydrous, Chromic (III) hydroxide, Chromic acid (H3CrO3), Dichromium trioxide hydrate, Chromium hydroxide (Cr(OH)3), HSDB 5796, EINECS 215-158-8, Chromic hydroxide [Chromium and chromium compounds], CrH3O3, MolPort-023-220-609, AKOS015913889, LS-53383, U341, I14-44887
Chromium hydroxide, Chromium(3+) hydroxide, Chromium(III) hydroxide, CID14787, 1308-14-1