Chromous Salt

Hydrogenation. Acetylene can be hydrogenated to ethylene and ethane. The reduction of acetylene occurs in an ammoniacal solution of chromous chloride (20) or in a solution of chromous salts in H2SO4 (20). The selective catalytic hydrogenation of acetylene to ethylene, which proceeds... 

Cbronioxydul-. chromous, chromium(II). -hy-drat, n. chromous hydroxide, chroinium(II) hydroxide. 8alz, n. chromous salt, chro-nuum(n) salt. verbiudung, /. chromous compound, chroinium(II) compound. 

Chloro 6-trichloromethyl pyridine (N-Serve ) Chromates, certain insoluble forms Chromic acid and chromates (as Cr) Chromium, soluble chromic and chromous salts (as Cr)... 

The chromous-chromic reaction is highly unstable because of the high instability of the chromous salt. This redox couple is only stable when the concentration of the chromous salt is 5 to 10 times higher than that of the chromic salt. This reaction has been studied60 in 1.0 JV H2S04, and the plots of AFoo/ V versus co-1/2 are given in Fig. 9. The value of a is 0.47 and fc° = 2 x 10-3 cm/s. The results (Table 3) are comparable to those obtained by direct current polarography. 

Toxicology. Chromium metal is relatively nontoxic. There is little evidence of significant toxicity from chromic or chromous salts, probably because of poor penetration of skin and mucous membranes. Dermatitis from some chromic salts has been reported. 

No ammonia additive compounds of chromous salts arc known, but certain salts unite with hydrazine, forming complex salts of the same type as the ammines. 

The chromi-ammines are produced by the action of ammonia and ammonium salts on chromic salts, or by the action of ammonia in presence of ammonium salts on chromous salts and subsequent oxidation. The second method is analogous to that for the formation of cobalt-ammines. The chromi-ammines form a group of coloured substances, and comprise unstable and stable derivatives, some of which are very complex. 

The salts may also be prepared by oxidising a solution of chromous salt in an aqueous solution of ammonium sulphate by means of iodine. The nitrate or the chloride is usually prepared first, and the other salts obtained from them by double decomposition. 

The product is practically insoluble in water and in boiling, dilute hydrochloric acid but if even a very little chromous salt is added, it dissolves rapidly, forming a green solution. The chromous salt may be secured by... 

They also tried soln. of cupric chloride in acetic acid, formic acid, acetone, and methyl and ethyl alcohols. With 0-37, 0-62, and 0-925 litre of soln. with a mol of cupric bromide, 0-515, 0-120, and 0-000 litre of nitric oxide were respectively absorbed. They also tried soln. of cupric bromide in ethyl alcohol. E. Peligot found that nitric oxide is absorbed by aq. soln. of stannous salts (vide infra) and chromous salts. According to G. Chesneau, a soln. of ckromous chloride absorbs nitric oxide in the ratio CrCl2 NO=3 1, and the blue liquid becomes dark red. When heated, the nitric oxide is not expelled as in the case of ferrous salts, but the liquid becomes greenish-brown, and the nitric oxide is reduced to ammonia or hydroxylamine. The action of nitric oxide on soln. of chromous salts was also studied by V. Kohlschiitter, and J. Sand and O. Burger. 

Of the chromous salts, the acetate is the most readily prepared and purified. Because of this fact and the fact that it reacts readily with acids, it is commonly used as the starting point for the preparation of other chromous compounds. 

Chromium. Chromium is not an easily analyzed element because three distinct standards are listed by OSHA (Tables IV and V ). One standard exists for hexavalent chromium, chromic acid and chromates, another standard for soluble chromium compounds and chromous salts, and another standard for insoluble chromium compounds and chromium metal. The permissible amount of chromium in air decreases as the oxidation state increases. The analysis of chromium is further complicated by the multiplicity of NIOSH methods for chromium compounds. Hexavalent chromium shall be collected on PVC filters, although a criteria document for chromic acid (14) specifies mixed cellulose ester filters. The analytical method described in the hexavalent... 

A variety of reducing metals,3,9 chromous salts,10 and lower va-... 

Chromous Compounds. Chromic solutions are reduced by zinc in acid solution or by other strong reducing agents to chromous ion, Cr or [Cr(H20)3] + +, which is blue in color. This solution and solid chromous salts are very strong reducing agents, and must be protected from the air. 

The chromous salts, derived from the oxide CrO, arc analogous to the salts of divalent vanadium, manganese, and iron. This is seen in the isomorphism of the sulphates of the type R" SOj-THgO. The stability of such salts increases in the order of the atomic number of the metal. The chief basic oxide of chromium is the sesquioxidc CraO, which is closely allied to ferric oxide, and, like the latter, resembles aluminium oxide. The hydroxide, Cr(OH)3, with bases yields chromites analogous to, but less stable than, the aluminates. Chromic sulphate enters into the formation of alums. The chromic salts are very stable, but in the trivaJent condition the metal shows a marked tendency to form complex ions, both anions and cations thus it resembles iron in producing complex cyanides, whilst it also yields compounds similar to the cobaltamines. 

Atomic Weight.—From a consideration of the vapour densities of volatile compounds of chromium, and from the application of Dulong and Petit s Law, it is obvious that the atomic weight of chromium is about 52—that is, three times the chemical equivalent of chromium in chromic salts, or six times its combining weight in derivatives of chromium trioxide. Chromium thus exhibits di-, tri-, and hexa-valency in the chromous salts, chromic salts, and chromates and diehromates respectively. 

The sesquioxide, Cr Oa, containing trivalent chromium, is an amphoteric oxide. It yields chromic salts, such as chromic chloride, CrCla, and sulphate, Cr2(S04)a, which are very stable and show great similarity to the ferric salts and to salts of aluminium as, for example, in the formation of alums. Since, however, chromic oxide functions as a weaker base than chromous oxide, the latter having a lower oxygen content, the chromic salts are more liable to hydrolysis than the chromous salts. This is well marked in the case of the chlorides. Again, in spite of the stability of chromic salts, only a slight tendency to form simple Cr " ions is exhibited, whilst complex ions are formed much more readily, not only complex anions, as in the case of iron and aluminium, but also complex cations, as in the extensive chromammine series. In this respect chromium resembles cobalt and platinum. 

Chromous Metaphosphate, CrlPOjla-—Attempts to produce this compound by the action of fused metaphosphoric acid on chromium or on chromous salts have not been successful, although the method succeeds for the ferrous analogue. ... 

Chromous Carbonate, CrCOj, is obtained as a grey amorphous precipitate by the action of an alkali carbonate on a solution of a chromous salt. It is soluble in water charged with carbon dioxide. When heated, carbon dioxide is evolved, lea ung a residue of chromium sesquioxide. 

JVet Tests.—The presence of chromium in solution and its state of oxidation may be indicated by the colour due to its ions thus Cr is green, Cr04" yellow, and Cr O," orange. The solutions of chromous salts are generally deep blue. Vhen hydrogen sulphide is passed into a solution of chromate in presence of an acid, the colour changes to green and sulphur is precipitated ... 

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