Chromium trioxide

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Chromium trioxide
Crude chromium trioxide by Doug's Lab.png
Impure chromium trioxide
Names
IUPAC name
Chromium trioxide
Other names
Chromic anhydride
Chromic acid anhydride
Chromium(VI) oxide
Identifiers
Jmol-3D images Image
Properties
CrO3
Molar mass 99.99 g/mol
Appearance Dark red solid
Odor Odorless
Density 2.7 g/cm3 (at 20 °C)
Melting point 197 °C (387 °F; 470 K)
Boiling point 250 °C (482 °F; 523 K) (decomposes)
164.8 g/100 mL (0 °C)
169 g/100 mL (25 °C)
172.6 g/100 mL (40 °C)
198.1 g/100 mL (100 °C)
Solubility Soluble in acetic acid, acetone, diethyl ether, nitric acid, sulfuric acid
Thermochemistry
73.2 J/mol·K
−589.3 kJ/mol
Hazards
Safety data sheet ScienceLab
Lethal dose or concentration (LD, LC):
80 mg/kg (rats, oral)
Related compounds
Related compounds
Chromium(III) oxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Chromium trioxide is an inorganic compound with the formula CrO3. It is a dark red/crimson solid, widely used in synthesis and industry. It is the acidic anhydride of chromic acid.

Properties

Chemical

Chromium trioxide reacts violently with ethanol and other organic compounds, causing it to combust.

Physical

Chromium trioxide is a dard red/crimson solid in its anhydrous form, and red-orange in aqueous solution. It is very soluble in water and soluble in some organic solvents, such as acetone or diethyl ether, as well as sulfuric acid.

Availability

Chromium trioxide is sold by various chemical suppliers, though due to its hazards it's not easy to get hold of.

Preparation

Chromium trioxide can be prepared by reacting a Cr(VI) containing compound, such as sodium chromate or dichromate with concentrated sulfuric acid.

H2SO4 + Na2CrO4 → CrO3 + Na2SO4 + H2O
H2SO4 + Na2Cr2O7 → 2 CrO3 + Na2SO4 + H2O

The solid compound is filtered using a fritted funnel.

Projects

  • Chrome plating
  • Instantaneous ignition of alcohols

Handling

Safety

Chromium trioxide is a powerful oxidizer, highly toxic, corrosive, and carcinogenic. Avoid contact with alcohols.

Storage

Chromium trioxide should be kept in plastic or glass containers, with a proper label and a hazard symbol, in a dry place. If you're using glass, a good idea would be to keep the glass container inside a plastic container.

Since the compound ignites alcohols on contact, keep it away from any source o volatile solvents or products containing alcohols.

Disposal

A reducing agent, such as sodium metabisulfite, sodium sulfite or sodium thiosulfate can be used to turn CrO3 into the less toxic Cr(III) oxide.

References

Relevant Sciencemadness threads