Alum KCr

If more than simple atoms are bound to a central atom, then the coordination number still refers to the number of near neighbors. For example, in solid potassium chrome alum, KCr(S04)2- 12H20, and also in its fresh aqueous solutions, the chromium-containing cation is... 

Probably the most common compound of +3 chromium is potassium chrome alum, KCr(SOi)r 12H20. We know that the twelve water molecules are distributed equally, six around Cr+a and six around K+. Potassium chrome alum is just one example of the general class of solids called alums which have a 4-1 ion, a +3 ion, two sulfates, and twelve molecules of water. In the dyeing industry chrome alum is used for fixing dyes to fabrics. 

KA](S04)2 I2H2O, are isomorphous with the chrome alums, KCr(S04)2 l2H20, and mixed crystals of any composition between the two extremes may be prepared by... 

Isomorphous substances often crystallize together from a mixed solution to form solid solutions, single crystals containing both substances. In a solid solution the different ions (such as Mn++ and Ca+ +) are arranged at random in the positions occupied by one kind of ion alone in a pure substance. For example, solid solu tions of chrome alum, KCr(S04)2 12HoO, and ordinary alum, KA1(S04) 12H20,... 

Reduction of a dichrbmate in aqueous solution produces chromic ion, Cr+ + + (really the hexahydrated ion, [Cr(H20) ]+ + +), which has a violet color. The salts of this ion are similar in formula to those of aluminum. Chrome alum, KCr S04)2 12H20, forms large violet octa-hedra. 

E. Hollmann gave y = 13-2 mm. at 17° to 19° and he also obtained values for solid soln. of the chromium and aluminium alums. H. Lescoeur and D. Mathurin found that over cone, sulphuric acid the alum loses half its water of crystallization and passes into a lilac-coloured powder which does not lose its colour at 75°. At 20°, the dissociation press., f mm. of the moist alum, KCr(S04)2 WH2O, is 15-25 mm. for m=13-05, and 15-0 for n=12-3 for w=12 l, p=9-8, and the violet powder produced when w=ll-8, has p=9-l. This value... 

Potash alum, KA1(S04)2.12H20, and chrome alum KCr(S04)2.12H20 crystallize from their respective aqueous solutions as regular octahedra in almost identical forms and are known to be isomorphous. Alum crystals are also easily formed by... 

Pale violet [Cr(OH2)6l is obtained in aqueous solution when [Cr207] is reduced by SO2 or by EtOH and H2SO4 below 200 K. The commonest salt containing [Cr(OH2)6l + is chrome alum, KCr(S04)2-12H20. 

Two preparative methods are known for potassium hexathiocyantochromate (III). Both involve the exchange of the ligand water with thiocyanate. In both cases chrome alum, KCr(S04)2.12H20 reacts with either a solution of KSCN or it is added as a solid to molten KSCN. Since the potassium salts of the complex anions are very hygroscopic, it is advantageous analytically to transform them to the pyridinium salts. For a long time, the complexes were known to be readily partially aquated. However, interest in the spectra of their solutions in various solvents dates from the mid-fifties. 

CsAl(SO 2 -12H20 iron alum [13463-29-1], KFe(SO12Rp- chrome alum [7788-99-0], KCr(SOimp- and chromoselenic alum [17855-06-0],... 

It is frequently said that the behavior of trivalent chromium resembles that of trivalent aluminum, presumably because of the similarity in radii of the tw o ions (A1+8, 0.45 A Cr+3, 0.55 A). The structures of the solid oxides, fluorides, and chlorides are analogous for the two metals, and both form salts of the alum type (for example, KA1(S04)2 12H20, KCr(SeC>4)2 12H20). Chromium(III) sulfide, (Cr2S3) like aluminum sulfide, cannot be made in aqueous systems. 

Dehydration of Chrome Alum In contrast with the previous example, it appears that the dehydration of KCr(SC>4)2 12H20 is insensitive to the presence of water vapor, though experiments did not extend to the lowest pressures (80-82). A possible explanation is that dehydration is promoted by retained intranuclear water. The rate of interface advance at 290 K increased by about one quarter at 100 Pa water vapor compared with that in vacuum. 

Basicity chrome alum CCRIS 7532 Chrome alum Chrome potash alum Chromic potassium sulfate Chromic potassium sulphate Chromium potassium bis(sulphate) Chromium potassium sulfate (1 1 2) Chromium potassium sulfate (CrK(S04)2) Chromium potassium sulphate Chromium(lll) potassium sulfate Crystal Chrome Alum EINECS 233401-6 Potassium chromic sulfate Potassium chromic sulphate Potassium chromium alum Potassium chromium disulfate (KCr(S04)2) Potassium disulphatochromate (III) Sulfuric acid, chromium(3 ) potassium salt (2 1 1). Mordant for dyeing fabrics uniformly [dodecahydratej mp = 89° d = 1.83 soluble in 4 parts H2O. 

N. W. Fischer observed that 100 parts of cold water dissolve 16-7 parts of the chrome alum. J. Locke found that a htre of water dissolves 243-9 grms. of KCr(S04)2.12H20, or 125-1 grms. of KCr(S04,)2- The aq. soln. of the violet salt has an acidic reaction, and when the salt has been precipitated many times by alcohol from its aq. soln. H. Baubigny and E. Pochard found that a soln. neutralized by ammonia with methyl-orange as indicator, gave crystals which had an acidic reaction and the soln. also reacts acidic after standing a little while. 

Fig. 2.7 A photomicrograph of typical nuclei formed on a surface of an alum crystal KCr(S04)2 I2H2O. (Reprinted from [30], with permission)...

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