Sciencemadness Discussion Board

CrO(O2)2 or Cr3+

Wrecking Bereserker - 3-4-2019 at 06:28

Doesn't dichromate react with H2O2 in acid medium to give out Cr3+ green solution then how is CrO(O2)2 is produced by the same way?

fusso - 3-4-2019 at 06:43

Chromium(VI) peroxide (CrO5) or chromium oxide peroxide is an unstable compound formed by the addition of acidified hydrogen peroxide solutions to solutions of metal chromates or dichromates, such as sodium chromate or potassium dichromate. The generally yellow chromates or orange dichromates turn to dark blue as chromium(VI) peroxide is formed. Chromate or dichromate reacts with hydrogen peroxide and an acid to give chromium peroxide and water.

CrO42− + 2 H2O2 + 2 H+ → CrO5 + 3 H2O

After a few seconds, the chromium(VI) peroxide decomposes to turn green as chromium(III) compounds are formed.[1] To avoid this decomposition, it is possible to stabilize chromium(VI) oxide peroxide in a water-immiscible organic solvent such as diethyl ether, butan-1-ol or amyl acetate by adding a layer of the organic solvent above the chromate/dichromate solution and shaking during the addition of hydrogen peroxide. In this way, the chromium(VI) peroxide (unstable in the aqueous phase in which newly formed) is dissolved in the immiscible organic solvent. In this condition it can be observed over a much longer period.

2 CrO5 + 7 H2O2 + 6 H+ → 2 Cr3+ + 10 H2O + 7 O2

woelen - 4-4-2019 at 23:20

You can get CrO5, coordinated to pyridine, as a solid, which can be kept around for quite some time. It has a nice blue/purple color.

CrO5 in ether or amyl alcohol is more stable than in water, but in those solvents it also fairly quickly decomposes. In once tried this. I extract CrO5 from an aqueous layer into ether and then pipetted the ether layer away and put this in another bottle. The next day, the deep blue solution had become colorless and at the bottom, there was a dark green precipitate (most likely impure Cr2O3).