Green chromic chlorides

The dichloro - tetra - aquo - chromic salt, [Co(NH3)2(XT02)4] [Ch HgO ClJ IIgO, is formed when the ammonium salt is mixed with green chromic chloride in water, the reaction being represented thus ... 

Twenty grams of powdered green chromic chloride are placed in a smaU rpund-bottomed flask and 60ml of freshly-distilled thionyl chloride are added. When evolution of gas has ceased, the mixture is refluxed for two hours, the excess liquid evaporated off in v and the product stored in a vacuum desiccator over pellets of solid alkali for at least ttheura. 

It has been found4 that a good yield may be obtained rapidly by allowing the commercially available green chromic chloride, CrCl8-6H20, in methanol to boil under reflux with ethylenedi-amine in the presence of metallic zinc. The product, hydrated tris(ethylenediamine)chromium(III) chloride, is obtained as a solid and is readily purified. An exactly similar procedure may be used for the complex of 1,2-propanediamine. 

The apparatus is shown in Fig. 314. Forty grams of green chromic chloride is placed in quartz flask c, which is placed in an electric furnace capable of delivering 650°C. The apparatus for generating and superheating CCU vapor is then attached. This apparatus consists of the 250-ml. distilling flask o with its superposed dropping funnel and a U tube Immersed in a silicone oil bath at 150°C. 

W. Traube and co-workers prepared cone. soln. of chromous chloride by the prolonged electrolytic reduction of aq. sola, of green chromic chloride, using lead plates as electrodes and employing a current desnity of 0-175 amp. per sq. dm. The electrolysis of chromous chloride soln., using an iron cathode, results in the formation of a cathodic deposit of metallic chromium mixed with chromium oxides. 

N. Bjerrum found the results did not agree with the velocity equation for monomolecular reactions but the results were better represented by velocity equations for two consecutive, bimolecular reactions, on the assumption that the reaction involves the sequence of changes [Cr(H20)4Cl2]Cl->[Cr(H20)5Cl]Cl2 ->[Cr(H20)e]Cl3. If x, y, z respectively denote the concentrations of these three salts, then dxjdt=—kix, and dxldt=k. It was found that at 25°, A i=0-C0272 -J-O-0000162/s, and A 2=(3I/s+0-005/s2)10—7, where s denotes the cone, of free hydrochloric acid. For soln. with M mols of dark green chromic chloride, the... 

J. Sand and F. Grammling measured the velocity with which the violet hexahydrate Uberates iodine from a mixture of potassium iodide and iodate, and found the results to be in agreement with the assumption that the molecule is Cr.2Cl0.12H2O, and not [Cr(H20)e]C33. H. W. Fischer found that the solubility of chromium hydroxide in an aq. soln. of green chromic chloride is not directly proportional to the cone, of the latter. A basic chloride is probably formed. From a soln. of chromium hydroxide in aq. chromic chloride, the former cannot be precipitated either by the addition of electrolytes or by the action of heat part of it is supposed VOL. XI. 2 0... 

Chromium(IH) chloride, chromic chloride, CrClj. Violet solid (Cr plus CI2, hydrate plus SOCI2) only soluble in water in presence of Cr. Forms many complexes including the hydrates [Cr(H20)6]Cl3 - violet, [Cr(H20)jCl]Cl2,H20 - green, [Cr(H20)4Cl2]Cl,2H20 - green. 

A series of tetraquo-dcrivatives containing two molecules of pyridine is also known. These have formula [Cr py2(H20)4]R3, and correspond in general properties to the diammino series. They are prepared from green hydrated chromic chloride, [CrCl2(H20)4]C1.2lI20, by treatment with pyridine, when it is transformed into the dihydroxo-diaquo-dipyri-dino-chloride, [Cr pya(H20)2(0H)2]Cl, and this on treatment with mineral acid changes into the tetraquo-salt.6... 

Experiment 183. — Add to a few cubic centimeters of potassium dichromate solution a little concentrated hydrochloric acid and a few drops of alcohol. Warm gently. Two important changes occur. The chromate is reduced to chromic chloride which colors the solution green the alcohol is oxidized to aldehyde, which is detected by its peculiar odor. (See Exp. in ( ).) The equation is —... 

Chromic chloride, C l3 6H20, forms several kinds of crystals, varying in color from violet to green, the solutions of which have similar colors. These diflEerent colors are due to the formation of stable complex ions (Fig. 25-3) ... 

Oxidation states of chromium - -2, - -3, and -f-6. Oi es of chromium chronate, FeCr204, and crocoite, PbCr04. Chromium metal and its alloys ferrochrome, alloy steels, stainless steel. The aluminothermic process (Goldschrtiidt process). Electrolytic chromium. Chromium trioxide, chromic acid, dichromic acid, potassium chromate, potassium didiromate, sodium chromate, lead chromate. Equilibrium between chromate ion and dichromate ion. Chrome-tanned leather. Chromic oxide (chrome green) chromic ion, chrome alum, chromic chloride, chromic hydroxide, chromite ion. Chromous compounds. Peroxy-chromic acid. 

An interesting form of isomerism, dependent on the formation of such cations, is exhibited by chromic salts, which usually exist in at least two modifications, the one green and the other violet or dark blue. In both varieties the chromium is in the same state of oxidation, but the non-metallic radicle, while apparently freely ionised in a violet solution, is only partly active in the green. Thus the chlorine in violet chromic chloride, CrQj.eHjO, is completely precipitated by the addition of a soluble silver salt, but in the ordinary green variety only one-third of See Vol. X. of this series. 

A solution of chromic chloride is readily obtained by the action of dilute hydrochloric acid on chromic hydroxide, or on chromium sesquioxide which has not been ignited this solution on evaporation yields an amorphous, deliquescent, green mass, soluble in water and in alcohol. The product on heating in hydrogen chloride or chlorine at temperatures above 250° C. becomes anhydrous, at the same time assuming the usual colour of the anhydrous salt. Basic chlorides are formed by... 

On progressive hydrolysis, chromic chloride gives rise to two soluble basic chlorides, Cr(OH)Cl2 and Cr(OH)2Cl, and an insoluble grey-green hydroxide. The compound, Cr(OH)2Cl, is never present in any large proportion, and the hydroxide is only formed upon addition of alkali. The formulae of the three compounds are probably [Cr H20)5(0H)]Cl2, [Cr(H20)4(0H)2]Cl, and Cr(H20)3(0H)3 respectively. 

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