Hydrogen cyanide

Properties

General
Name	Hydrogen cyanide
Chemical formula	HCN
Appearance	Colourless liquid
Physical
Formula weight	27.0 amu
Melting point	260 K (-13 °C)
Boiling point	299 K (26 °C)
Density	0.7 ×103 k/m3
Solubility	very soluble
Thermochemistry
ΔfH0gas	135.14 k/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
Safety
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
SI units were used where possible. Unless otherwise stated, standard conditions were used. Disclaimer and references

Hydrogen cyanide, also known as formonitrile, is the chemical compound with chemical formula HCN (with the carbon atom (C) being triple bonded to the nitrogen atom (N)).

Hydrogen cyanide is highly poisonous. It is colorless and has a faint, bitter, almond-like odor. Some people are unable to smell cyanide at all, due to a genetic trait. The melting point is at -14°C and the boiling point is at 26°C.

Hydrogen cyanide is weakly acidic and partly converts to the cyanide ion CN^– in aequous solution. Such a solution is called prussic acid or hydrocyanic acid. The salts of hydrogen cyanide are known as cyanides.

Hydrogen cyanide 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. It can be produced by reacting a cyanide salt with a strong acid, or directly from ammonia and carbon monoxide.

Fruits that have a pit, such as cherries or apricots, often contain small quantities of hydrogen cyanide in the pit. Bitter almonds from which almond oil and flavoring is made also contain hydrogen cyanide. Hydrogen cyanide is contained in the exhaust of vehicles, in tobacco smoke and in the smoke of burning plastics. A deep blue pigment called Prussian Blue, used in the making of blueprints, also contains hydrogen cyanide.

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.

A mixture of hydrogen cyanide gas and air is explosive.