Hydrocyanic acid HCN

Whether gaseous or in aqueous solution, hydrocyanic acid has no action on aluminium. This acid and its solution can thus be stored and transported in aluminium alloy vessels. Aluminium equipment can be used in production plants for hydrocyanic acid. 

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Hydrocyanic acid, HCN, also known as prussic acid, or formo-nitrile, is the product of decomposition of numerous glucosides found in a very large number of plants, usually together with some other volatile compound, so that essential oils containing hydrocyanic acid do not, for practical purposes, exist in the first instance as such in the plant, but are only developed on the decomposition of the glucoside. 

Another example of an acid is hydrogen cyanide, HCN, which transfers its proton to water when it dissolves to form the solution known as hydrocyanic acid, HCN(aq). However, only a small fraction of the HCN molecules donate their protons, and so we classify HCN as a weak acid in water. We write the proton transfer reaction with equilibrium half-arrows ... 

This value shows that NH4+ is a weaker acid than boric acid (pKa = 9.14) but stronger than hydrocyanic acid (HCN, pKa = 9.31). 

The rate of reaction between hydrocyanic acid (HCN) and acetaldehyde (CH3CHO) to give acetaldehyde cyanohydrin has been studied in a constant-volume batch reactor at 25°C in dilute aqueous solution, buffered to keep the pH constant (Svirbely and Roth, 1953). The reaction is... 

For the reaction between hydrocyanic acid (HCN) and acetaldehyde (CH3CHO) in aqueous solution,... 

Cyanide ion, CN , reacts with Fe " to form the blue dye that is used in blueprint paper. Hydrocyanic acid, HCN(aq), is a weak acid, with... 

A). Cyanide ions (CN ) enter the organism in the form of hydrocyanic acid (HCN) the latter can be inhaled, released from cyanide salts in the acidic stomach juice, or enzymatically liberated from bitter almonds in the gastrointestinal tract The lethal dose of HCN can be as low as 50 mg. CN binds with high affinity to trivalent iron and thereby arrests utilization of oxygen via mitochondrial cytochrome oxidases of the respiratory chain An internal asphyxiation (histotoxic hypoxia) ensues while erythrocytes remain charged with O2 (venous blood colored bright red). 

Glycosides that have soaplike properties are called saponins. Similarly, glycosides that liberate hydrocyanic acid (HCN) on hydrolysis are known as cyanogenic glycosides, and glycosides that have an effect on heart muscle are called cardiac glycosides. 

Cyanides. These are compds contg the monovalent radical,-CN, derived from hydrocyanic acid (HCN). See AC in Vol 2 of Encycl, pC 167-L. Some of the more important salts ate the following ... 

J.6 Determine the salt that is produced from the acid-base neutralization reaction between (a) potassium hydroxide and acetic acid, CH3COOH (b) ammonia and hydroiodic acid (c) barium hydroxide and sulfuric acid (both H atoms react) (d) sodium hydroxide and hydrocyanic acid, HCN. Write the full ionic equation for each reaction. 

With his colleague Louis-Jacques Thenard (1777-1857), Gay-Lussac did considerable work with electrochemistry to produce significant amounts of elemental sodium and potassium, highly reactive and useful substances that were used to isolate and discover the element boron. Gay-Lussac also completed extensive studies of acids and bases and was the first to deduce that there were binary (two element) acids such as hydrochloric acid (HC1) in addition to the known oxygen-containing acids like sulfuric acid (H2S04). Additionally, he was able to determine the chemical composition of prussic acid to be hydrocyanic acid (HCN) and was considered the foremost practitioner of organic analysis. 

Sodium cyanide is the salt of the weak hydrocyanic acid, HCN (ionization = 0.01 per cent in 0.1 equivalent solution), and the strong base, sodium hydroxide. A solution of this salt shows an alkaline reaction to litmus, thus demonstrating that the solution contains an appreciable quantity of OH ions. This is the result of hydrolysis, and the process may be explained as follows ... 

The salt, in accordance with the general rule for salts, will exist in solution in the ionized condition. Water is in equilibrium with a very small number of its own ions. But even the small number of H+ ions thus furnished to the solution is more than can exist in presence of the large concentration of CN ions of the salt. Undissociated hydrocyanic acid, HCN, must form but since this removes some of the H+ ions, the equilibrium between water and its ions is temporarily destroyed. The equilibrium must be reestablished through the ionization of more water. This cycle of reactions repeats itself a great many times until complete equilibrium among all the components is established. When this condition is reached, as really happens in a very short time, there has been a considerable accumulation of OH- ions and of an equivalent amount of un-ionized HCN. 

Dilute hydrochloric acid hydrocyanic acid, HCN, with an odour reminiscent of bitter almonds, is evolved in the cold. It should be smelled with great caution. A more satisfactory method for identifying hydrocyanic acid consists in converting it into ammonium thiocyanate by allowing the vapour to come into contact with a little ammonium polysulphide on filter paper. The paper may be conveniently placed over the test-tube or dish in which the substance is being treated with the dilute acid. Upon adding a drop of iron(III) chloride solution and a drop of dilute hydrochloric acid to the filter paper, the characteristic red colouration, due to the iron(III) thiocyanate complex, Fe(SCN)3, is obtained (see reaction 6 below). Mercury(II) cyanide is not decomposed by dilute acids. 

Heptane C7H16 Hexane C6H14 Hydrocyanic acid HCN... 

Hydrocyanic acid, HCN Cyanic acid, HOCN Thiocyanic acid, HSCN Hydrazoic acid, HN3... 

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