Potassium salt of hydrocyanic acid

Synonyms/Trade Names Potassium salt of hydrocyanic acid... 

The two simple salts of hydrocyanic acid which are used in the synthesis of organic cyanogen compounds are potassium cyanide, K—(CN), and silver cyanide, Ag—(CN). These are both prepared by the action of the metallic oxides or hydroxides on the acid. 

The thiocyanates are generally soluble in water, the exceptions being those of lead, silver, mercury and copper. Most of them dissolve also in alcohol and ether. Aqueous solutions of the alkali thiocyanates undergo atmospheric oxidation under the influence of sunlight with solutions of medium concentration this change takes place rapidly, with separation of a yellow, amorphous precipitate consisting of pseudocyanogen sulphide, (CNS)3 (cf. p. 236). The concentration of thiocyanate most favourable to the separation of this sulphide is about 50 per cent, in summer and 10 per cent, in winter. In addition to this substance the products of the photochemical oxidation of potassium thiocyanate include hydrocyanic acid, sulphate, carbon dioxide, ammonia and ammonium salts ... 

Like the analogous ferri- and cobalti-cyanides it is decomposed by potassium hydroxide, and also by concentrated hydrochloric acid, in the latter case with evolution of hydrocyanic acid. With certain metallic salts it yields characteristic precipitates. Thus, with ferrous salts a white precipitate is obtained with ferric, a bright yellow. 

I. Prussian Blue Reaction. To the distillate is added a drop of ferric chloride and a drop of ferrous sulphate solution, or only a drop df ferrous sulphate solution, a this generally contains a UtUe of the ferric salt this is then made alkaline with a little sodium or potassium hydroxide, well shaken and carefully acidified with hydrochloric acid. In the presence of hydrocyanic acid, a precipitate of Prussian blue is formed, or the liquid turns green and deposits blue flakes on standing. 

It forms soft, flexible, lemon-yellow crystals, permanent in air at ordinary temperatures. They begin to lose Aq at 60° (140° F.), and become anhydrous at 100° (213° F.). Soluble in HaO insoluble in alcohol, which precipitates it from its aqueous solution. When calcined with KHO or KaCOs, potassium cyanid and cyanate are formed, and Fe is precipitated. Heated with dilute HaSOi, it yields an insoluble white or blue salt, potassium sulfate, and hydrocyanic acid. Its solutions form with those of many of the metallic salts insoluble ferrocyanids those of Zn, Pb, and Ag are white, cupric ferrocyanid is mahogany-colored, fer-... 

Synonym(s) Formonitrile hydrocyanic acid prussic acid Cyanide of sodium hydrocyanic acid sodium salt Cyanide of potassium hydrocyanic acid, potassium salt Calcid calcyan cyanide of calcium... 

The nature Of the ions.—In 1814, G. F. Parrst12 found that in the electrolysis of aq. soln. of potassium ferrocyanide the alkali accumulated about the negative pole, and ferric oxide and hydrocyanic acid about the positive pole, and the work of J. F. Daniell and W. A. Miller, and of W. Hittorf (1859), showed that double salts are of two kinds, and that in the one kind the metal is bound as a complex negative ion, and in the other it is the positive ion. For example, in the electrolysis of potassium silver cyanide, KCy.AgCy, W. Hittorf (1859) found that silver was deposited on the cathode, whereas with salts of the type AgN03 it is deposited on the anode. Hence, it was inferred that the salt ionizes KAgCy2=K,- -AgCy2 similarly,... 

The above methods cannot be used if the spirit contains chlorides, as may happen if it has been broken down with water containing these salts. In this case the total hydrocyanic acid may be determined by distilling 100 c.c. of the spirit and collecting at least three-quarters (which will contain all the hydrocyanic acid present) in a dilute solution of silver nitrate of known titre. The liquid is then made up to a definite volume and filtered, the excess of silver in an aliquot part of the filtrate being titrated with thiocyanate as already described. The free hydrocyanic acid, in presence of chlorides, should be determined colorimetrically as follows a solution of about 0-05 gram of potassium cyanide per litre is prepared and its exact content of HCN determined by titration with silver nitrate and ammonium thiocyanate. In a series of test-tubes are placed such quantities of this... 

SYNS CYANIDE of POTASSIUM CYANIDES (OSHA) CYANURE de POTASSIUM (FRENCH) HYDROCYANIC ACID, POTASSIUM SALT KALIUM-CYANID (GERMAN) POTASSIUM CYANIDE, solution pOT) RCRA WASTE NUMBER P098... 

The Prussian blue reaction may be rendered more convenient in use by employing a reaction paper. For this purpose Ganassini s paper is strongly recommended. It is prepared by immersing a strip of filter paper, just before use, in a mixture of 10 ml. 10% ferrous sulphate solution (containing a trace of ferric salt) and 20 ml. of an alkaline solution of Rochelle salt (30 gm. Rochelle salt, 10 gm. potassium hydroxide and 100 ml. water). This paper should be exposed first to the atmosphere containing hydrocyanic acid and then to hydrochloric vapour, when it becomes greenish-blue. 

Hydrocyanic acid is most easily prepared from its potassium salt, K(CN), which is obtained principally by the decomposition of the complex double cyanides of iron as we shall soon consider. The acid is also obtained by the hydrolysis of certain glucosides, e.g., amygdalin, in bitter almonds. It is prepared synthetically by reactions to be discussed presently in connection with the constitution of it and its salts. It is a colorless liquid with a characteristic odor and burns with a violet flame. It boils at 26.1 and solidifies to crystals which melt at —14°. It is an extremely strong poison the best antidotes being chlorine and hydrogen dioxide. It is readily absorbed by metallic nickel which is thus used in gas masks for this purpose. It is stable in dry air but in presence of water is readily hydrolyzed yielding ammonia and formic acid as the chief products. 

These two simple salts are not known but with hydrocyanic acid, with potassium cyanide, with themselves or with each other, they form well known double cyanides. These double cyanides, however, are really simple compounds which dissociate, in solution, into two ions, viz., the cation, of hydrogen or the metal, and a complex anion, consisting of iron and the cyanogen group. 

There are many chemical forms of CN organic CNs, nitriles, CN salts, hydrocyanic acid, and the anionic form. For the sake of discussion, the term CN refers in general to CN without reference to chemical form. However, where appropriate, chemical form is referenced (i.e., hydrogen cyanide, HCN potassium cyanide, KCN and sodium cyanide, NaCN). 

HCN has the chemical synonyms of formonitrile, pmssic acid, and hydrocyanic acid. Some physicochemical properties are compared with those of the sodium, potassium, and calcium salts in Table 14.1. Relevant to the toxicity and hazards of HCN are its hquid state at NTP, poor ionization, low molecular weight (MW), low boiling point, high vapor pressure, low vapor density (0.947 at 31°C), and hence ready diffusibility. The salts are sohds that are readily soluble in water, ionize, and in spite of low vapor pressure they hydrolyze in moist conditions with the hberation of HCN, this being markedly increased under acidic conditions. 

SYNONYMS (potassium cyanide) cyanide of potassium, hydocyanic acid potassium salt, (sodium cyanides) cyanide of sodium, hydrocyanic acid sodium salt, prussiate of soda. 

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