Difference between revisions of "Chromium(VI) oxide peroxide"

Revision as of 17:46, 2 November 2022

Chromium(VI) oxide peroxide, also known as chromium(VI) peroxide or chromium pentoxide (CrO₅) is an unstable compound formed by the addition of an acidified hydrogen peroxide solution to solutions of metal chromates, such as sodium or potassium chromate, and followed by extraction from aqueous solution with an organic solvent, such as diethyl ether.

Properties

Chemical

Chromium(VI) peroxide is not very stable in water, and will rapidly decompose to Cr(III) ions, releasing oxygen.

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

It can be stabilized by the addition of an solvent immiscible with water, such as diethyl ether, ethyl acetate, during the addition of the hydrogen peroxide.

Chromium peroxide will form a complex with pyridine and bipyridine, which is one of the few ways of stabilizing the compound.

Physical

Chromium(VI) oxide peroxide is a very unstable deep blue compound. It is soluble in water, but rapidly breaks down, and soluble as well as stable in solvents such as diethyl ether, ethyl acetate, amyl alcohol and its esters (formiate, acetate, butyrate, valerate), amyl chloride, valeric ether. It is insoluble in many other solvents, such as aniline, benzene, bergamot oil, CCl₄, CS₂, castor oil, kerosene, ligroin, nitrobenzene, paraffins, terpene alcohols, toluene, wintergreen oil.^[1]

Availability

Chromium peroxide is not sold by any entity due to its instability and has to be made in situ.

Preparation

The addition of an acidified solution of 3% hydrogen peroxide to sodium chromate will cause it to turn from yellow to dark blue-brown. The chromate salt reacts with hydrogen peroxide and an acid to give chromium peroxide, water, and the metal salt of the acid.

Na₂CrO₄ + 2 H₂O₂ + 2 H⁺ → CrO₅ + 3 H₂O + 2 Na⁺

Diethyl ether or ethyl acetate is added to stabilize the product.^[2]

The dissolution of chromium trioxide in crushed ice, followed by the addition of cooled diethyl ether and finally cooled hydrogen peroxide (at 0 °C) is added. The solution is shaken and the water layer frozen on an ice bath.^[3]

Potassium peroxochromate can also be used instead of potassium chromate.^[4]

Projects

• Ether test for chromates

Handling

Safety

Chromium(V) oxide peroxide is a strong oxidizer, but it's generally too unstable to pose any serious risk. However, if produced in high quantity, it may spontaneously explode.

Storage

Chromium(V) oxide peroxide cannot be stored, as it rapidly decomposes.

Disposal

Since it quickly breaks down to Cr(III) in water, it can be simply poured down the drain. Though it's best to decompose it first, for safety reasons.

References

1. ↑ Journal of the American Chemical Society; vol. 17; (1895); p. 41 - 43
2. ↑ https://www.youtube.com/watch?v=MjDgXQb4_DU
3. ↑ Wiede, O. F.; Ber.; vol. 31; (1898); p. 516 - 524
4. ↑ Byers, H. G.; Reid, E. E.; American Chemical Journal; vol. 32; (1904); p. 503 - 513

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