Chromium trioxide

(Chromic anhydride; chromic acid; chromium(VI) oxide; chromic trioxide; chromium oxide)

CAS 1333-82-0





Physical Properties

Dark red flakes or crystals

mp 196 °C, bp: decomposes at 250 °C

Very soluble in water (62 g/100 mL)


Flash Point



Toxicity Data

LD50 oral (rat)

80 mg/kg



0.1 mg (CrO3)/m3 (ceiling)



0.05 mg (Cr)/m3

Major Hazards

Probable human carcinogen (OSHA "select carcinogen"); severely irritating to the skin and mucous membranes; very strong oxidizing agent.


Chromium trioxide and other chromium(VI) salts are moderately toxic substances by ingestion; 1 to 15 g may be a fatal dose in humans. Ingestion of nonlethal doses of these compounds can cause stomach, liver, and kidney damage; symptoms may include clammy, cyanotic skin, sore throat, gastric burning, vomiting, and diarrhea. Chromic acid is irritating to the skin, and prolonged contact can cause ulceration. Inhalation of chromate dust or chromic acid mist can result in severe irritation of the nose, throat, bronchial tubes, and lungs and may cause coughing, labored breathing, and swelling of the larynx. Eye contact with chromium trioxide and its solutions can cause severe burns and possible loss of vision.

Occupational exposure to chromium(VI) compounds has been related to an increased risk of lung cancer. Several hexavalent compounds of chromium, including chromium trioxide, are listed in IARC Group 1 ("carcinogenic to humans") and are classified as "select carcinogens" under the criteria of the OSHA Laboratory Standard. Long-term exposure to chromium trioxide or chromium(VI) salts may cause ulceration of the respiratory system and skin. Exposure to chromium trioxide by inhalation or skin contact may lead to sensitization. Chromium trioxide has exhibited teratogenic activity in animal tests.

Flammability and Explosibility

Chromium trioxide is not combustible but is a strong oxidizing agent and can accelerate the burning rate of combustible materials. Contact with easily oxidized organic or other combustible materials (including paper and oil) may result in ignition, violent combustion, or explosion. The use of dry chemical, carbon dioxide, Halon, or water spray extinguishers is recommended for fires involving chromium(VI) compounds.

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