Chromium hydroxide Cr

Another reason chemists find the above complex ion picture of aqueous solutions useful is that it is easily extended to explain amphoteric behavior. Take the case of chromium hydroxide, Cr(OH)3, a good example of an amphoteric hydroxide. It dissolves very little in water, but is quite soluble both in acid and in base. Presumably it can react with either. How can this behavior be explained in terms of the complex ion picture ... 

Chromate, dichromate, permanganate, chlorate and hypochlorite and other oxidants are readily reduced hy hydrazine for example, removal of chromate from wastewater may he achieved fuUy hy converting water-soluhle chromate to insoluble precipitate of chromium hydroxide, Cr(OH)3 ... 

Chromium in its Compounds is sometimes metallic and sometimes non-metallic toward the other components. Thus, in chromium trioxide, CrOg, the anhydride of the hypothetical chromic acid, H2Cr04, chromium acts as a non-metal, just like sulphur in sulphuric acid hence in chromates the chromium is acidic, or non-metallic, in its chemical relations with the other elements. In chromic compounds, however, chromium acts as a metal. Thus chromium hydroxide, Cr(OH)3, is analogous to aluminium hydroxide chrome alum is potassium chromium sulphate, and is analogous to aluminium alum. The two classes pass into each other by appropriate operations,... 

Among these compounds only chromium hydroxide Cr(OH)j (in bold characters) is insoluble. 

The oxide Cr203 is better described as an amorphous chromium hydroxide, Cr(OH)3. The conversion coating is yellow to brown in color. 

The formed oxide, given as Cr203, is probably better described as amorphous chromium hydroxide, Cr(OH)3. ITie color of the formed conversion coating is yellow to brown and typical coating weights range from 0.3 to 2.0 g/m . Those layers can be used as a primer for a paint layer or powder coating but can also be applied unpainted. 

Figure 3.13 Planes of chromium hydroxide Cr(OH)3(OH2)3. [Cr(OH)3(OH2)3j octahedra are connected by the bridging ligand [H302] ...

None of the Cr(III) products from Equations 6 or 7 are effective crosslinkers since a chromic aqua ion must be hydrolyzed first to form olated Cr to become reactive. Colloidal and solid chromium hydroxides react very slowly with ligands. In many gelation studies, this critical condition was not controlled. Therefore, both slow gelation times and low Cr(VI) Cr(III) conversion at high chromate and reductant concentrations were reported (9,10). 

Fig. 1.1.7 Complex solutes present in solutions of chrome alum, which on aging yield monodispersed amphorous spherical chromium hydroxide panicles. A labeled solution initially 4.0 X 10 4 mol dm-3 in chrome alum was heated at 75°C for 9 days. After cooling and filtering off the particles, the filtrate was subjected to paper electrophoresis. The corresponding solutes are (A) Cr1+, (B) Cr,(0H)2S042+. (C) Cr(OH)2, (D) Cr(0H)S04 and Cr(OH).,. (From Ref. 36.)...

The preparation of ferric azide failed, however, due to the formation of basic ferric azide. A complex compound was obtained by Martin from chromium hydroxide and hydrazoic acid. It contained no chromium or N ions and has the probable formula of a complex compound [Cr(N3)4]H. 

Cr(0H)(S04) Chromium hydroxide sulfate Chromium(III) hydroxide sulfate... 

Solid chromium(lll) hydroxide, Cr(OH)3, reacts with aqueous chlorate ions, CIO3, in basic conditions to form chromate ions, CrO2, and chloride ions,Cl. ... 

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. 

Chromium Chlorate, Cr(C10g)3, which is obtained by the double decomposition of barium chlorate and chrome alum, forms a violet solution which becomes green at 65° C. and decomposes on boiling, yielding chromium hydroxide and oxides of chlorine. Tire dcconr-position is facilitated by potassium ferricyanide. The salt is used iir calico printing and for increasing the permanence of aniline black. 

Chromium Perchlorate.—By dissolving chromium hydroxide in perchloric acid, and subsequent cautious evaporation, short green deliquescent needles of chromium perchlorate, soluble in alcohol, arc obtained. Two bluish-green perchlorates, probably derivatives of the hex-aquo base, [Cr(H20)e](0104)3 and [Cr(H20)6](C104)3.3lI 0, liave been described. ... 

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