Chromic acid s. Chromium

Chromic acid (s. a. Chromium trioxide) 31, 219 Chromium carbonyl compds. 

Chromic acid (s. a. (Chromium trioxide) 31, 219 Chromium s. a. Chromyl. Chromium(II) acetate 32, 520 Chromium carbonyl compds. 

Workplace. The Occupational Safety and Health Administration (OHSA) has estabUshed workplace permissible exposure limits (PEL) for chromium metal and three forms of chromium compounds. OSHA s PEL for chromic acid and chromates is 0.1 mg/m 3 both a ceiling, ie, no exposure above this concentration is allowed, and an 8-h time-weighted average (TWA). Chromium metal and insoluble chromium salts have an 8-h TWA PEL of 1.0 mg/m Cr, and the same standard is 0.5 mg/m Cr for soluble Cr(III) and Cr(II) compounds (144). 

In 1979, a viable theory to explain the mechanism of chromium electroplating from chromic acid baths was developed (176). An initial layer of polychromates, mainly HCr3 0 Q, is formed contiguous to the outer boundary of the cathode s Helmholtz double layer. Electrons move across the Helmholtz layer by quantum mechanical tunneling to the end groups of the polychromate oriented in the direction of the double layer. Cr(VI) is reduced to Cr(III) in one-electron steps and a colloidal film of chromic dichromate is produced. Chromous dichromate is formed in the film by the same tunneling mechanism, and the Cr(II) forms a complex with sulfate. Bright chromium deposits are obtained from this complex. 

EPA, 1993. U.S. EPA, Office of Air Quality Planning and Standards, "Chromium Emissions from Chromium Electroplating and Chromic Acid Anodizing Operations Background Information for Proposed Standards," EPA-453[R-93-030a, Research Triangle Park, NC, July 1993. 

Oxidation of isopropyl alcohol by chromic acid in concentrated acetic acid solution has recently been studied by Wiberg and Schafer S spectrophotometri-cally. At 385 nm a rapid increase in absorbance (with a half life of about 6 sec) due to mono- and diester formation was noted. When the reaction was examined at 510 nm, first a rapid increase, then a decrease of the absorbance was found. Since at this wavelength only chromium species can absorb, the intermediate could be chromium(V) or (IV). The esr spectra of reaction mixtures showed a relatively sharp signal with a. g = 1.9805 value corresponding to chromium(V). The fact that the relative concentrations of the intermediate determined from the spectral data agree well with the intensity of esr signals, indicates that the same species is responsible for the both phenomena. It is then clear that the oxidation of isopropyl alcohol proceeds via chromium(V). 

In 1996, the ISEE system was used to remove 200 g of hexavalent chromium from 16 yd of soil at the U.S. Department of Energy s (DOE s) Unlined Chromic Acid Pit located at the Sandia National Laboratory s (SNL s) Chemical Waste Landfill in Albuquerque, New Mexico. The treatment costs for this 4-week demonstration were 1368/yd. According to the U.S. EPA, these costs were calculated for the ISEE prototype used during the demonstration. The costs for a full-scale system would be lower due to design improvements and efficiency of scale (D22781Q, pp. 65, 66 D22758R, pp. 44-51). 

It was there that he discovered a new metal which, because of the red color that its salts acquire when heated, he named erythronium (44). Upon further study, however, he decided that he was mistaken, and that the brown lead ore from Zimapan was a basic lead chromate containing 80.72 per cent of lead oxide and 14.80 per cent of chromic acid (12). His paper therefore bore the modest title, Discovery of chromium in the brown lead of Zimapan (21). In 1805 Collet-Descotils confirmed del Rio s analysis (22), and for twenty-five years no more was heard of the new element, erythronium. 

In 1961, Brown348 described the oxidation of alcohols, using a two-phase system with aqueous chromic acid and diethyl ether. Brown s oxidation349 has a work-up, facilitated by the reluctance of ether to form emulsions with materials containing chromium, and although not as popular as Jones oxidation, it is used quite often. 

Synonym (s) Sulfuric acid, chromium (III) salt No data Chromium dioxide Chromic acid, diamonium salt... 

Synonym(s) Chromic acid, calcium salt Chromic acid, chromium anhydride Chromic acid, lead salt Chromic acid, dipotassium salt... 

Adachi S. 1987. Effect of chromium compounds on the respiratory system Part 5. Longterm inhalation of chromic acid mist in electroplating by C57BL female mice and recapitulation on our experimental studies. Jpn J Ind Health 29 17-33. 

Oxidation in acidic solution can be achieved by Caro s acid, for example at 85 °C.247 This chemistry is employed in the extraction of chromium from superalloy scrap.248 It can also be used to detoxify, recover or re-cycle effluents from chromic acid oxidation or pickling liquors. Detoxification and recovery of chromic acid solutions is by the addition of hydrogen peroxide which reduces the chromium(III) salts, followed by alkali to precipitate and separate chromium hydroxide.249 Re-cycle can be by direct re-oxidation with Caro s acid, or by first raising the pH to alkaline levels, oxidation with hydrogen peroxide and re-acidification with subsequent salt by-product production. 

General Properties of Chromium Compound.s—Chromium and Hydrogen— Halogen and Oxyhalogen Compounds—Oxides and Hydroxide.s— Chromites—Chromic Acid—Chromates, Dichromates, and Polyohromates— Perohromio Acid and Perehromate.s—Compounds with Sulphur, Selenium, and Tellurium. 

Again, chromic acid is found to contain twice as much oxygen for the same an. unt of chromium, or it may be represented as Cr, Og. This being a most improbable formula, we observe next, that chromic acid may be substituted for sulphuric acid, without change of form in other words, these acids are isomorphous. But the formula of sulphuric acid is S 0., and we, therefore, conclude, that the formula of chromic acid is Cr 0, j which agrees perfectly with the first observation, that it contains twice as much oxygen for the same weight of chromium as the oxide does for Cr O3 is the very same proportion as Cr 0 . 

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