Chrome alum solutions

The formation of rnonodisperse amorphous, spherical particles of chromium hydroxide is offered here as an example. These dispersions are readily obtained by simply heating chrome alum solutions (35). It was established experimentally that the sulfate ion was essential in order to obtain uniform dispersions thus, when chromium nitrate solutions were aged, monodispersed particles were produced only if a sulfate salt was introduced into the reaction. 

Figure 1.1.19 illustrates such hematite particles coated with chromium hydroxide in which the latter was produced by the hydrolysis of a chrome alum solution in the presence of a-Fe203 cores on aging the dispersion at 85°C. For greater efficiency the chromium salt solution was either preheated or preheated with KOH (but avoiding precipitation of chromium hydroxide) (144). 

Figure 3b Transmission electron micrograph showing a bright field image of a small secondary nucleus produced by contact with a (100) face of a potash alum parent crystal in a supersaturated chrome alum solution.

For the student interested in crystal growth, potassium aluminum sulfate, also called alum, is a salt available in most pharmacies. It will form single crystals relatively easily from a supersaturated solution. Alum crystals are octahedral in shape and colorless. The related compound, chromium aluminum sulfate dodecahydrate, called chrome alum, forms dark-purple octahedral crystals. Mixing various proportions of supersaturated alum and chrome alum solutions allows the growth of mixed crystals that resemble amethysts in color. (The more alum in the mix, the lighter the purple color of the crystal.) Take the powder patterns of crnshed pnre alum and crushed pure chrome alum, and a mixture of the two compounds. After yon have grown some mixed crystals, crush some and take their powder pattern. Is it different from the two pure materials and from the mixture Explain your observations. 

Tissue sections must be mounted on subbed microscope slides m order to avoid detachment of the sections dunng the hybridization procedure. Subbing m a gelatin/chrome alum solution is an efficient and inexpensive method. Poly-L-lysine may also be employed (12). 

Ohio, high carbon ferrochromium is leached with a hot solution of reduced anolyte plus chrome alum mother Hquor and makeup sulfuric acid. The slurry is then cooled to 80°C by the addition of cold mother Hquor from the ferrous ammonium sulfate circuit, and the undissolved soHds, mostiy siHca, are separated by filtration. The chromium in the filtrate is then converted to the nonalum form by conditioning treatment for several hours at elevated temperature. 

The mother Hquor from the cmde ferrous sulfate crystallisation contains neady all the chromium. It is clarified and aged with agitation at 30°C for a considerable period to reverse the reactions of the conditioning step. Hydrolysis reactions are being reversed therefore, the pH increases. Also, sulfate ions are released from complexes and the chromium is converted largely to the hexaaquo ion. Ammonium chrome alum then precipitates as a fine crystal slurry. It is filtered and washed and the filtrate sent to the leach circuit the chrome alum is dissolved in hot water, and the solution is used as cell feed. 

Table 5. Solution Concentrations in Electrolysis of Chrome Alum, g/L...

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... 

As an example of the problem of species in solution, consider the case of a solution made by dissolving some potassium chrome alum, KCrfSO s-12H20, in water. On testing, the solution is distinctly acidic. A currently accepted explanation of the observed acidity is based upon the assumption that, in water solution, chromic ion is associated with six H20 molecules in the complex ion, Cr(H20) a. This complex ion can act as a weak acid, dissociating to give a proton (or hydronium ion). Schematically, the dissociation can be represented as the transfer of a proton from one water molecule in the Cr(H20) 3 complex to a neighboring H20 to form a hydronium ion, H30+. Note that removal of a proton from an H20 bound to a Cr+3 leaves an OH- group at that position. The reaction is reversible and comes to equilibrium ... 

V. P. Gorodnov, A. Yu. Ryskin, G. P. Kharlanov, A. A. Belov, and A. V. Shein. Enhancing oil recovery from boreholes— by injecting into seam aqueous solution of polyacrylamide, chrome alum and bentonite clay for improved flow characteristics. Patent SU 1731942-A, 1992. 

Fig. 1.1.7 Complex solutes present in solutions of chrome alum, which on aging yield monodispersed amphorous spherical chromium hydroxide panicles. A labeled solution initially 4.0 X 10 4 mol dm-3 in chrome alum was heated at 75°C for 9 days. After cooling and filtering off the particles, the filtrate was subjected to paper electrophoresis. The corresponding solutes are (A) Cr1+, (B) Cr,(0H)2S042+. (C) Cr(OH)2, (D) Cr(0H)S04 and Cr(OH).,. (From Ref. 36.)...

Chromous sulfate (aqueous) A fresh solution 0.4 M in chrome alum and 0.05 M in sulfuric acid is contacted with lightly amalgamated Zn... 

Use a 3% to 5% solution of sodium metabisulfite, a 3% solution of chrome alum, or a mildly acid stop bath, such as Kodak SB-1 Nonhardening Stop Bath. Or use a very gentle-acting stop bath, suggested by Jay Dusard, comprised of a solution of 10.0 grams of sodium bisulfite in 1.0 liter of water. 

Uses Preservative for pyro solutions in acid fixing baths and bleaching solutions in chrome alum fixing baths. 

Dry test (flame colouration) Potassium compounds, preferably the chloride, colour the non-luminous Bunsen flame violet (lilac). The yellow flame produced by small quantities of sodium obscures the violet colour, but by viewing the flame through two thicknesses of cobalt blue glass, the yellow sodium rays are absorbed and the reddish-violet potassium flame becomes visible. A solution of chrome alum (310 g 1), 3 cm thick, also makes a good filter. 

J)) Mix equal small quantities of potassium carbonate, potassium nitrate, and powdered chrome alum, place the mixture on a platinum foil, and hold it with the forceps in the upper Bunsen flame so that the mixture will fuse. If a platinum foil is not available, use a porcelain crucible. A yellow mass, due to the presence of potassium chromate, results. If the color is not decided, dissolve the mass in water, add acetic acid, slowly at first, and boil to expel the carbon dioxide. Add a few drops of lead nitrate solution to a portion, and yellow lead chromate is precipitated. (Compare Exp. 177 (e).) If the precipitate is white, it is lead carbonate, and shows that not all the potassium carbonate was decomposed, as intended. 

Experiment 185. — (a) Add a little sodium hydroxide solution to a solution of chrome alum. The precipitate is chromic hydroxide. Describe it. Add an excess of sodium hydroxide solution and shake. Describe the result Boil, and state the result. 

Add a little, and then an excess, of ammonium sulphide to a solution of chrome alum. Compare the result with that in ( ). Docs chromium form a sulphide Do aluminium and zinc ... 

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. 

What chemical reactions are taking place when a violet solution of chrome alum on treatment with hydrochloric acid turns green in color ... 

Chromium Chlorate, Cr(C10g)3, which is obtained by the double decomposition of barium chlorate and chrome alum, forms a violet solution which becomes green at 65° C. and decomposes on boiling, yielding chromium hydroxide and oxides of chlorine. Tire dcconr-position is facilitated by potassium ferricyanide. The salt is used iir calico printing and for increasing the permanence of aniline black. 

Chromic oxide jellies may be formed by adding sodium or potassium hydroxide or ammonia to a solution of chromic sulphate or chloride containing sodium acetate or by adding sodium or potassium hydroxide, hut not ammonia, to a solution of chrome alum. The jelly is violet if prepared by the addition of ammonia or of a slight excess of the alkali metal hydroxide if the latter is added in larger quantity the jelly is green. The jellies dissolve in hydrochloric acid, but re-form on neutralising the solution if sufficient sodium acetate is present. 

Cobalt Chromite, CoO.CrgOg, is obtained by the addition of sodium carbonate to a mixed solution of chrome alum and cobalt chloride, and igniting the precipitate. ... 

The aqueous solution (blue, with a reddish tinge, but becoming green at 50° to 70° C.) deposits violet octahedra of the several forms in which chrome alum crystallises, including the rhombic dodecahedron, cube, and trapezohedron, the octahedron is the most stable. The crystals have a density of about 1-84, a specific heat of 0-324, and a coefficient of expansion of 0-0000246. The transformation of the violet to the green variety takes place at 78° C., - the substance melting at 89° C.ii to a green mass. Other physical constants have been determined, and the absorption spectra of its aqueous solution, studied. ... 

Chromic Orthophosphates.—Violet chromic phosphate, CrPO. BHgO, is produced as a lavender amorphous precipitate when cold solutions of equal weights of chrome alum and ordinary sodium phosphate are mixed ... 

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