[Chemistry Class Notes] Hydrocyanic Acid Pdf for Exam

HCN acid name is hydrogen cyanide, a highly volatile, colourless, and extremely poisonous liquid. It has a boiling point 26° C and freezing point -14° C. A solution of the compound in water is named prussic acid. It was discovered in 1782 by a Swedish chemist, Carl Wilhelm Scheele, who prepared it from the pigment Prussian blue. Hydrogen cyanide compounds are used for several chemical processes, including fumigation, hardening of iron and steel, electroplating. Therefore the concentration of ores. It also is employed in the preparation of acrylonitrile, which is used in the production of acrylic fibres, synthetic rubber, and plastics.

Hydrogen cyanide is very toxic because it inhibits cellular oxidative processes. Humans can survive 50–60 parts of the compound per million parts of air for an hour without severe costs, but exposure to concentrations of 200–500 parts per million of air for a half-hour is typically fatal. A method of inflicting execution consists of administering a deadly dose of the compound gas.

Hydrogen cyanide is an excellent solvent for several salts, but not widely used as a solvent due to its toxicity. In pure form, the compound may be stable, but it polymerizes readily within the presence of essential substances, like ammonia or cyanide. The salts used in the extraction of ores, in electrolytic processes, and the treatment of steel. Organic compounds such as aldehydes and ketones, forming cyanohydrins, which function intermediates in many organic syntheses.

HCN Structure

The chemical formula of hydrocyanic acid is HCN. Its molecular formula is written as CHN, and its molar mass is 27.03 g/mol. Hydrogen cyanide may be a simple planar molecule, with a triple bond between the carbon and nitrogen atoms.

HCN Occurrence

HCN occurs naturally in the pits of certain fruits such as cherries, apples, and apricots, and the fruit pits contain small amounts of cyanohydrins from HCN.

HCN Preparation

HCN is prepared on a laboratory scale by the addition of acids to cyanide salts of alkali metals (such as NaCN, KCN, etc.):

HCl + NaCN → HCN + NaCl

HCN Physical Properties

HCN is found as a pale blue, colourless transparent liquid (hydrocyanic acid) or a colourless gas (hydrogen cyanide). Hydrocyanic acid features a density of 0.687 g/mL, and boils slightly above temperature, at 25.6 °C (78.1 °F). It has a distinct smell of bitter almonds, which is used to identify the presence of this highly poisonous material.

HCN Chemical Name

Its chemical name is hydrogen cyanide, which is a weak acid, and partially ionizes in water to give H+ (or H3O+) and the cyanide anion, CN–.

HCN + H2O → H3O+ + CN–

It reacts with bases to form salts called cyanides.

HCN + KOH → KCN + H2O

Uses of HCN

Despite its toxicity, HCN is a necessary reagent used in the production of a variety of useful industrial chemicals such as sodium cyanide, potassium cyanide, methyl methacrylate (monomer used for making polymers and plastics), chelating agents EDTA and NTA, as well as the polymer Nylon. HCN is also used to prepare pesticides and chemical warfare agents.