Chromous oxide

Chromium hexacarbonyl decomposes on strong heating (explodes around 210°C). The product is chromous oxide, CrO. In inert atmosphere the products are chromium and carbon monoxide. It also is decomposed by chlorine and fuming nitric acid. Photochemical decomposition occurs when its solutions are exposed to light. 

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 Oxide, CrO, is obtained by the oxidation in air of chromium amalgam or, preferably, by the action of dilute nitric acid upon chromium amalgam. It is a black powder which inflames when struck with a pestle, or when heated in the air, but not in a vacuum, and bums, forming the sesquioxide. It is insoluble in nitric acid and in dilute sulphuric add, but in hydrochloric acid it dissolves, forming a blue solution and liberating hychogen in accordance with the equation ... 

When an air-free solution of caustic potash is added to a solution of chromous chloride in absence of air, a brownish-yellow precipitate of chromous hydroxide, Cr(OH)2, is obtained which may be dried over sulphuric acid. On heating in the presence of an inert gas this does not yield chromous oxide, since it decomposes according to the equation ... 

Chromous oxide 2701 CrO Chrome green green oxide of chromium monoxide of chromium protoxide of chromium. 

USE In catalysts for olefin polymerization and isomerization gasoline additive to increase octane number prepn of chromous oxide, CrO. 

Recently, Griffith and his co-workers (5) have shown, from a study of thermoelectric potentials, that although chromic oxide is a p-type semiconductor in oxygen, it becomes n-type in pure hydrogen. This is presumably associated with a partial reduction of the surface to chromous oxide (< , 6). A similar result had been reported earlier for chromia-alumina catalysts both by Chaplin, Chapman, and Griffith (7) and by Weisz, Prater, and Rittenhouse 8), but in view of the ra-type semiconductor properties of pure alumina (9,10), it is not clear whether measurements on chromia-alumina in hydrogen give information on the chromia or the alumina. 

The behavior of chromic oxide in a hydrogen atmosphere is also complex. It is reasonable to interpret the maximum in Fig. 3 as the point at which reduction of the surface to chromous oxide begins to play a major role. Such a reduction is thermodynamically possible only if the water partial pressure is sufficiently low (6). If the development of n-type properties occurs only when there is appreciable reduction to chromous oxide, treatment with moist hydrogen should leave chromic oxide a p-type semiconductor. It would be of considerable interest to confirm this. 

J. D. F. Marsh North Thames Gas Board, England) We have measured the thermoelectric potential of chromia reduced at 500° in H2 and found that it is an n-type semiconductor even if this H2 is saturated with water at room temperature, that is, under conditions where bulk chromous oxide is not stable. Thus, addition of water to dry reduced catalyst does not cause a shift to beyond the maximum resistivity, as postulated in the last paragraph of the paper (Lecture 22), and the increase in resistivity follows naturally from the observed decrease in the amount of chemisorbed hydrogen. 

CrO Chromous oxide or chromium monoxide (CrO) is a vaporization product (52) of Cr203, and has been studied as a hydrate (53), CrO HaO, Chromous oxide is of astrophysical interest (54). 

H. Moissan said that the amalgam is less fluid than mercury and J. Fer e, that it decomposes in air into chromous oxide and mercury. G. Tammann and... 

When a sat. soln. of potassium dichromate is cooled to —16° and treated with 2 per cent, soln. of hydrogen dioxide at the same temp., a white, solid substance separates and the soln. turns blue. If a cold sat. soln. of sodium acetate is added to this soln., it assumes the lake-colour of chromous acetate, and if left for half an hour the green colour of chromic acetate appears. Solid chromous acetate may be obtained by extracting the blue soln. with ether and adding sodium acetate to the blue ethereal soln. The electrical conductivity of the blue ethereal soln. of chromous oxide is less than 2 X 10 at 0°. The simplest explanation of these facts is said to be that chromic acid is reduced to the chromous state by hydrogen dioxide, and a liigher oxide of hydrogen, is produced. 

E. M. Peligot, if kept out of contact with air it gives a brown precipitate of hydrated chromous oxide q.v.) accompanied by the evolution of hydrogen. W. Traube and co-workers found that the precipitation of soln. of chromous salts by alkali-lye gives a mixture of hydrated chromous and chromic oxides in var3ring proportions. 

Under this system chromium(II) oxide is named chromous oxide. We do not use this older system in this text. 

An older naming system substftutes the names found in this column for the name of the metal and its char. Under this system, chmmlum(ll) oxide is named chromous oxide. Additionally, the suffix -ous indicates the ion with the lesser char and -tc indicates the Ion with the gieater chaige. We will not use the older system in this text... 

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