Chromium and manganese

Chemical ingenuity in using the properties of the elements and their compounds has allowed analyses to be carried out by processes analogous to the generation of hydrides. Osmium tetroxide is very volatile and can be formed easily by oxidation of osmium compounds. Some metals form volatile acetylacetonates (acac), such as iron, zinc, cobalt, chromium, and manganese (Figure 15.4). Iodides can be oxidized easily to iodine (another volatile element in itself), and carbonates or bicarbonates can be examined as COj after reaction with acid. 

Silver-silver chloride electrode 63, 553, (T) 554 Silylation (ch) gas, 236 liq, 219 Simultaneous spectrophotometric D chromium and manganese, 712 Sintered glass filtering crucibles 102 Soda lime 477... 

Spectrophotometric determinations - continued D. or concn. of potassium nitrate, 710 D. of simultaneous, chromium and manganese, 712... 

Which of the elements vanadium, chromium, and manganese is most likely to form an oxide with the formula MO, Explain your answer. 

There are no data available for testing the predicted numbers 0.22 and 1.22 of unpaired electron spins for chromium and manganese, respectively. 

Other metal oxide catalysts studied for the SCR-NH3 reaction include iron, copper, chromium and manganese oxides supported on various oxides, introduced into zeolite cavities or added to pillared-type clays. Copper catalysts and copper-nickel catalysts, in particular, show some advantages when NO—N02 mixtures are present in the feed and S02 is absent [31b], such as in the case of nitric acid plant tail emissions. The mechanism of NO reduction over copper- and manganese-based catalysts is different from that over vanadia—titania based catalysts. Scheme 1.1 reports the proposed mechanism of SCR-NH3 over Cu-alumina catalysts [31b],... 

General sonochemical studies of both chromium and manganese have been reported separately due to strong oxidising nature of these ions. However, comparative strength of their oxidising powers, in an ultrasonic field, is of some technical... 

Pankaj, Chauhan (2004) Sonochemical studies of aqueous solutions of chromium and manganese in their cationic and oxoanionic states. Ind J Chem 43(A) 1206-1209... 

Dusts of magnesium, zirconium, titanium and some magnesium-aluminium alloys [1], and (when heated) of aluminium, chromium and manganese [2], when suspended in carbon dioxide atmospheres are ignitable and explosive, and several bulk metals will bum in the gas. 

A graphite furnace procedure has been described [674] for the direct determination of iron, chromium, and manganese in seawater and estuarine waters in which the interference normally associated with the presence of sodium chloride is eliminated. The technique requires only very small sample volumes (10-20 il) for the atomisation stage. The reproducility of the method was very good. Sensitivities of 0.4,0.2, and 0.07 xg/l and precisions of determination of 4.5,3, and 11% (at 2 xg/l level) were obtained for iron, manganese, and zinc. 

Nickel may be a factor in asbestos carcinogenicity. The presence of chromium and manganese in asbestos fibers may enhance the carcinogenicity of nickel (USEPA 1980), but this relation needs to be verified. Barium-nickel mixtures inhibit calcium uptake in rats, resulting in reduced growth (WHO 1991). Pretreatment of animals with cadmium enhanced the toxicity of nickel to the kidneys and liver (USPHS 1993). Simultaneous exposure to nickel and cadmium — an industrial situation... 

In the titanosilicate system, cyclic voltametric measurements had indicated (Section III.D) that the electron density at the tripodal sites is higher than at the tetrapodal sites. Hence, by analogy with the chromium and manganese complexes, we may expect the tripodal sites to favor hydrogen abstraction and allylic CH oxidation, although electron transfer and epoxidation occur preferentially on the tetrapodal sites. 

Hydrogen transfer reactions from an alcohol to a ketone (typically acetone) to produce a carbonyl compound (the so-caUed Oppenauer-type oxidation ) can be performed under mild and low-toxicity conditions, and with high selectivity when compared to conventional methods for oxidation using chromium and manganese reagents. While the traditional Oppenauer oxidation using aluminum alkoxide is accompanied by various side reactions, several transition-metal-catalyzed Oppenauer-type oxidations have been reported recently [27-29]. However, most of these are limited to the oxidation of secondary alcohols to ketones. 

Hypovanadous oxide resembles the metal in many of its properties. It is insoluble in water, but dissolves in acids without evolution of hydrogen to yield the lavender-coloured solutions which are characteristic of solutions of hypovanadous salts. These salts are, however, most conveniently prepared in solution by electrolytic reduction in an inert atmosphere of solutions of vanadium pentoxide in the various acids.7 Hypovanadous salts are isomorphous with salts of divalent iron, chromium, and manganese. On being treated with caustic alkalis, a brown precipitate of hypovanadous hydroxide, V(OH)a, is obtained, which rapidly oxidises to the greyish-green vanadous hydroxide, V(OH)s. 

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