Chromium neutral compounds

Neutral Solvated Mono(Organo)chromium(III) Compounds... 

From the description given, the reactant is solid ammonium dichromate, (NH4)2Cr207(s), and the products are nitrogen gas, N2(g), water vapor, H20(g), and solid chromium(III) oxide, Cr203(s). The formula for chromium(III) oxide can be determined by recognizing that the Roman numeral III means that Cr3+ ions are present. For a neutral compound the formula must then be Cr203, since each oxide ion is O2-. 

Chromium(iii) complexes of the ligands PO " and HjPO" have been prepared. The neutral compound [Cr(P04KNH3)j],2H20 and salts of the complex cation [Cr(H2P04XNH3)5] were characterized by spectroscopic studies. The thermal decomposition of [Cr(en)3]P04,3H20 takes place in several stages, represented by Scheme 3. 

Coatings, Paints, and Pigments. Various slightly soluble molybdates, such as those of zinc, calcium, and strontium, provide long-term corrosion control as undercoatings on ferrous metals (90—92). The mechanism of action presumably involves the slow release of molybdate ion, which forms an insoluble ferric molybdate protective layer. This layer is insoluble in neutral or basic solution. A primary impetus for the use of molybdenum, generally in place of chromium, is the lower toxicity of the molybdenum compound. 

The final consideration for the manufacture of Cr(III) compounds is the mole ratio of acid to Cr. This ratio determines the basicity value of the product. Basicity can also be stated as the amount of positive charge on chromium (ITT) neutralized by hydroxide. For example, is 0% basic,... 

Neutralizing removes the large amount of hexavalent chromium from the surface of the part. Hexavalent chromium shortens the life of the catalyst, and trace amounts completely inhibit electroless nickel deposition. The neutralizer is usually a mildly acidic or basic reducing agent, but other types of neutralizers are available, especially for substrates that are difficult to plate. The neutralizer may also contain surfactants (qv) or other compounds that increase catalyst absorption absorption promoters are often needed for non-ABS plastics. 

The precipitate is soluble in free mineral acids (even as little as is liberated by reaction in neutral solution), in solutions containing more than 50 per cent of ethanol by volume, in hot water (0.6 mg per 100 mL), and in concentrated ammoniacal solutions of cobalt salts, but is insoluble in dilute ammonia solution, in solutions of ammonium salts, and in dilute acetic (ethanoic) acid-sodium acetate solutions. Large amounts of aqueous ammonia and of cobalt, zinc, or copper retard the precipitation extra reagent must be added, for these elements consume dimethylglyoxime to form various soluble compounds. Better results are obtained in the presence of cobalt, manganese, or zinc by adding sodium or ammonium acetate to precipitate the complex iron(III), aluminium, and chromium(III) must, however, be absent. 

Cr03 As a transition metal, chromium forms more than one stable cation. Name the metal first, using a Roman numeral to designate chromium s charge. Each of the three oxide anions has a -2 charge. To maintain net charge neutrality, Cr must be +6, so the name of the compound is chromium(VI) oxide. 

Chromium hydroxide is an amphoteric compound and exhibits minimum solubility in the pH range of 7.5 to 10.0. Effluents from chromium reduction processes should be neutralized to the range of zero solubility (pH 8.5 to 9.0) to minimize the amount of soluble chromium remaining in solution. 

In groundwater, hexavalent chromium tends to be mobile due to the lack of solubility constraints and the low adsorption of CH6 anion species by metal oxides in neutral to alkaline waters (Calder 1988). Above pH 8.5, no CH6 adsorption occurs in groundwater Cr adsorption increases with decreasing pH. Trivalent chromium species tend to be relatively immobile in most groundwaters because of the precipitation of low-solubility Cr 3 compounds above pH 4 and high adsorption of the Cr+3 ion by soil clay below pH 4 (Calder 1988). 

Elemental composition (neutral CuCr04) Cu 35.39%, Cr 28.97%, 0 35.64%. These chromates are analyzed hy x-ray, thermogravimetic analysis (the basic form loses water around 260°C) and metal analysis. Copper and chromium may he analyzed hy digesting the compound(s) with nitric acid, diluting appropriately with water, followed hy AA, ICP, or other instrumental analysis, (see Chromium and Copper). 

These hydroxo-salts are all sulphur-yellow crystalline substances. The acid residues are hydrolysable and hence outside the co-ordination complex, and the aqueous solutions, unlike the hydroxo-salts of chromium-and cobalt-ammines, are neutral to litmus, a fact which Werner suggests is due to the smaller tendency of the hydroxo-radicle attached to ruthenium to combine with hydrogen ions. This tendency is much less than in the case of the ammines of cobalt and chromium, but that it still exists is indicated by the increased solubility of these hydroxo-compounds in water acidified with mineral acids, and from such solutions aquo-nitroso-tetrammino-ruthenium salts are obtained thus ... 

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