Chromic anhydride

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Chrome anhydride

 

Oxide chromium(VI) (chromium trioxide, chromium trioxide, chromic anhydride), CrO3 — chromium compound with oxygen, dark red crystals, soluble in water. The anhydride of chromic and dichromic acids.

 

Physical properties

Black and red with a purple hue the crystals, plates or needles. Hygroscopic, deliquescent.

melting point=196 °C at atmospheric pressure it decomposes below the boiling point.

Density 2.8 g/cm3; solubility in water, and 166 g/100 g (15 °C), 199 g/100g (100 °C).

 

Chemical properties

CrO3 — acidic oxide. When it is dissolved in water, it forms chromic acid (with the lack CrO3) or dichromic acid (with an excess of CrO3).

When the interaction of CrO3 with alkalis formed chromates.

When heated above 250 °C decomposes with the formation of chromium oxide(III) and oxygen.

Like all compounds of Cr(VI), CrO3 is a strong oxidizing agent (restored to Cr2O3). For example, ethanol, acetone and many other organic substances ignite or even explode when exposed to them (although some reference point "is soluble in alcohol and ether"). Oxidizes iodine, sulfur, phosphorus, coal.

Complex chromium trioxide with pyridine is used for the oxidation of alcohols in the appropriate carbonyl compound(reaction Caretta).

Get the action of H2SO4 on sodium dichromate Na2Cr2O7 (less potassium dichromate K2Cr2O7).

 

Application

 

Used to obtain chromium by electrolysis, electrolytic chromium plating; chromating galvanized parts, as a strong oxidizer, occasionally in pianostaff.

Apply also, as the oxidizing agent in organic chemistry (in the production of isatin, Indigo, etc D.).

In mixture with diatomaceous earth is used for purification of acetylene called "apura".

Solutions chromic anhydride (or, more often, of potassium dichromate) in sulfuric acid is widely used in the laboratory to clean glassware of organic pollution (chrome mixture).

Also used for:

• For obtaining pure chromium, tverdosplav.

• In the process of chrome plating (coating a layer of chromium) and chromate (dip galvanized parts in a solution anhydride, which generates on the surface a solid film of zinc oxide), passivation.

• For some types catalysts, foundry mixtures, metal etching.

• As an oxidizing agent in chemical reactions.

• In the synthesis of organic dyes for example, Indigo, isatine.

• For the purification of acetylene.

• For the preparation of chromium compounds for removal of vessels from the laboratory of organic contaminants.

• Included with some piratasdaweb.

• In rockets to ignite fuel.

 

 

Oxide chromium(VI) is very toxic as many other compounds of hexavalent chromium. The lethal dose for human ingestion of 0.08 g/kg.

Chrome anhydride is a highly reactive substance that can cause at contact with organic substances, fire and explosions. When hit skin irritation, eczema and dermatitis, and can also to trigger the development of skin cancer. Even with prompt removal from skin sheets leaves spots of brown. Very dangerous inhalation of fumes chromic anhydride, although readily available and nonvolatile.

Storage it is applied sealed glass or porcelain dishes must the elimination of contact with organic substances. It requires the use of overalls and means of individual protection.

 

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