Chrome alum green

The halogenates of chromium, uranium, and manganese.—The double decomposition of chrome alum and barium chlorate, or a soln. of chromic sulphate and potassium chlorate, furnishes a violet liquid containing chromium chlorate,134 which becomes green at 65°. Even at ordinary temp, the soln. smells of chlorine at 100°, chlorine gas is given off and the liquid becomes reddish-yellow—it contains chromic... 

Other chemicals that can be used to make stop baths are boric acid, citric acid, and sodium bisulfite. Chemicals that should not be used are chrome alum and potassium salts, such as potassium metabisulfite or potassium sulfite, either of which can cause green stains on some enlarging papers. In addition, the introduction of potassium salts into a fixing bath can convert the bath to potassium thiosulfate, which is nearly inactive as a fixing agent.1... 

The Cr (aq) ion occurs, for example, in [Cr(OH2)6]Cl3 and in the chrome alums, MCr(S04)-12H20. There are several stable isomers of the chloride among these the dark green frani -[CrCl2(0H2)4]Cl-2H20 is the commercially available salt. 

Experiment 181. — ( ) Prepare a borax bead (see page 231), touch it with a minute quantity of any chromium compound, e.g. chrome alum, and heat in both the oxidizing and reducing flame. The green ,olor is a characteristic and delicate test for chromium. 

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. 

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. 

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. ... 

Acid Clirmnic Orthophosphate, CrH8(P04)2.8H20, has been described. It forms asymmetric crystals of the colour of the chrome alums stable in air. Yauquelin obtained an emerald green uncrystallisable solution by acting upon the hydrated sesquioxide of chromium with aqueous phosphoric acid. 

Derivation (1) Interaction of solutions of chromium chloride and sodium phosphate (2) by mixing chrome alum and disodium hydrogen phosphate. Violet, amorphous powder (not the hexahydrate) is formed that becomes crystalline on contact with water. On boiling, it is converted into green crystalline hydrate. 

Dodecahydrate, chrome alum ammonium. Small dark-violet Or violet-blue, octahedral, cubic crystals ruby-red by transmitted light, mp 94 loses 9H20 on melting and the remaining H.O by 300". tl25 1.72. Readily sol in water slightly sol in alcohol. Aq soln is violet when cold, green when hot. 

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