|Formula weight||27.0 amu|
|Melting point||260 K (-13 °C)|
|Boiling point||299 K (26 °C)|
|S0gas, 1 bar||201.82 J/mol·K|
|S0liquid, 1 bar||113.01 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|
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 aqueous 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.
Hydrogen cyanide gas in air is explosive at concentrations over 56,000 ppm.