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Hydrogen cyanide

Name Hydrogen cyanide
Chemical formula HCN
Appearance Colourless liquid
Formula weight 27.0 amu
Melting point 260 K (-13 °C)
Boiling point 299 K (26 °C)
Density 0.7 ×103 kg/m3
Solubility very soluble
ΔfH0gas 135.14 kJ/mol
ΔfH0liquid 109 kJ/mol
ΔfH0solid 100 kJ/mol
S0gas, 1 bar 201.82 J/mol·K
S0liquid, 1 bar 113.01 J/mol·K
S0solid ? J/mol·K
Ingestion Extremely toxic. Early symptoms include nausea, vomiting and abdominal pain.
Inhalation Extremely dangerous. Early symptoms include slow breathing rate, irritation.
Skin Poisoning is thought to be possible through the skin.
Eyes Dilated pupils are a symptom of poisoning.
More info Hazardous Chemical Database (http://ull.chemistry.uakron.edu/erd/chemicals/7/6581)
SI units were used where possible. Unless otherwise stated, standard conditions were used.

Disclaimer and references

Hydrogen cyanide (HCN), also known as formonitrile, is a colorless, volatile, and extremely poisonous chemical compound whose vapors have a bitter almond odor. It is produced in large quantities all over the world by the chemical industry where it is used in tempering steel, dyeing, explosives, engraving, the production of acrylic resin plastic, and other organic chemical products.

The carbon atom (C) is triple bonded to the nitrogen atom (N). The compound melts at -14°C and boils at 26°C. A simple way to produce the gas is by reduction of potassium ferrocyanide solution.

Hydrogen cyanide is weakly acidic and partly converts to the cyanide ion CN in solution. Such a solution is called prussic acid or hydrocyanic acid.

An HCN concentration of 300 parts per million of air will kill a human in a few minutes. The toxicity is caused by the cyanide ion. The mechanism of this toxicity, and the uses of the poison, are described on the cyanide page.

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