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It is the acidic anhydride of chromic acid, and is sometimes marketed under the same name. [6] This compound is a dark-purple solid under anhydrous conditions and bright orange when wet. The substance dissolves in water accompanied by hydrolysis. [clarification needed] Millions of kilograms are produced annually, mainly for electroplating. [7]
Because of its considerable stability, chromia is a commonly used pigment. It was originally called viridian. It is used in paints, inks, and glasses. It is the colorant in "chrome green" and "institutional green." Chromium(III) oxide is a precursor to the magnetic pigment chromium dioxide, by the following reaction: [7] Cr 2 O 3 + 3 CrO 3 → ...
This kind of chromic acid may be used as a cleaning mixture for glass. Chromic acid may also refer to the molecular species, H 2 CrO 4 of which the trioxide is the anhydride. Chromic acid features chromium in an oxidation state of +6 (and a valence of VI or 6). It is a strong and corrosive oxidizing agent and a moderate carcinogen.
At yet lower pH values, further condensation to more complex oxyanions of chromium is possible. Both the chromate and dichromate anions are strong oxidizing reagents at low pH: [6] Cr 2 O 2− 7 + 14 H 3 O + + 6 e − → 2 Cr 3+ + 21 H 2 O (ε 0 = 1.33 V) They are, however, only moderately oxidizing at high pH: [6] CrO 2− 4 + 4 H 2 O + 3 e ...
Further condensation reactions can occur in strongly acidic solution with the formation of trichromates, Cr 3 O 2− 10, and tetrachromates, Cr 4 O 2− 13. [2] All polyoxyanions of chromium(VI) have structures made up of tetrahedral CrO 4 units sharing corners. [3] The hydrogen chromate ion, HCrO 4 −, is a weak acid: HCrO − 4 ⇌ CrO 2−
CrO3 dissolves in water to make a solution containing H+ and CrO4-- ions, which is a dilute solution of chromic acid. Interestingly, CrO3 shows acid properties without water being present e.g. CaO + CrO3 --> CaCrO4. It is an example of a "Lewis acid" which meets the (broader) definition of an acid suggested by the chemist G.N.Lewis in the 1920s.
Structure of CrO(O 2) 2 (pyridine).Hydrogen atoms bonded to carbon atoms are omitted. Color code: Cr = gray, C= black, H = white, O= red, N = blue. Chromium(VI) oxide peroxide is formed by the addition of acidified hydrogen peroxide solutions to solutions of metal chromates or dichromates, such as sodium chromate or potassium dichromate.
It is readily oxidized by the atmosphere. CrO is basic, while CrO 3 is acidic, and Cr 2 O 3 is amphoteric. [3] CrO occurs in the spectra of luminous red novae, which occur when two stars collide. It is not known why red novae are the only objects that feature this molecule; one possible explanation is an as-yet-unknown nucleosynthesis process. [4]