Anhydrous alums

Alum. Gram-molecules dissolved per Litre of Water. Grams of (Anhydrous) Alum per Litre of Water. 

A study of the (NH4)2S04-In2(S04)3 system confirmed the existence of the anhydrous alum NH4In(S04)2, together with the sulphate (NH4)3In(S04)3, which exists in two (a and /3) forms. The high-temperature (0) form is rhombohedral.558... 

T. Klobb obtained mixed crystals of the anhydrous sodium and ammonium chromium sulphates, (NH4,Na)S04.Cr2(S04)3, by melting together chromic sulphate or chrome-alum with ammonium and sodium sulphates. The hexagonal crystals are isomorphous with the anhydrous alums. A. N. Bach found the transition temp, to be between 60° and 70°. 

Figure 2.11 The layered structure of the anhydrous alums, AM(S04)2- The M sites are shown as octahedra, the [S04] groups as tetrahedra and the A" " cations as spheres. The topology of the M sites is also shown...

M(0H)3 should dissolve in both acids and alkalis M salts will tend to form basic salts the sulfate should form alums M2S3 should be precipitated by H2S or (NH4)2S anhydrous MCI3 should be more volatile than ZnCl2... 

As previously stated, Wohler was unable to obtain metallic aluminum by Oersted s method. However, since the latter encouraged him to continue his attempts, he prepared some anhydrous aluminum chloride by Oersted s method, and devised a new plan for isolating the metal. After adding an excess of hot potassium carbonate solution to a boiling hot solution of alum, he washed and dried the precipitated aluminum hy-... 

Salts should have tendency to form basic salts, the sulfate should form alums the sulfide should be precipitated by HaS or (NHi) S. The anhydrous chloride should be more volatile than zinc chloride,... 

Salts readily hydrolyze and form basic salts alums are known the sulfide is precipitated by H,S and by (NH<),S under special conditions The anhydrous chloride is more volatile than zinc chloride... 

Evaporation of solutions of alumina in sulfuric acid yields crystals of A12(S04)3T6H20. If a group I sulfate is also present, the products are alums MA1(S04)2T2H20, in which aluminum exists as [Al(OH2)fi]3+. Analogous selenates but not tellurates have been prepared. Basic salts, e.g. Al2(OH)2(SO4)210H2O, and solids obtained from aluminum sulfate solutions above 100 °C also contain complex ions in which the coordination sphere of Al3+ is occupied by OH groups and/or water molecules rather than sulfate ions. Thermal decomposition of the hydrate A12(S04)3-16H20 yields practically anhydrous A12(S04)3 at 450 °C further decomposition to... 

The normal sulphates show a marked tendency to the formation of double salts,8 the best known case being that of the alums, which are isomorphous compounds of the general formula M2(S04)3.X2S04. 24H20, where M and X represent a tervalent and univalent metal, respectively in aqueous solution these double salts are almost entirely resolved into the ions of their constituent salts,9 recombination taking place as the solution crystallises. Double salts are also formed by the crystallisation of fused mixtures of anhydrous sulphates, the freezing-... 

Sodium Rhodium Sulphate, NasS04.Rh2(S04)3, was first prepared by Bunsen3 by heating sodium rhodium sulphite with concentrated sulphuric acid. Tliis salt was regarded by Seubert and Kobbe 4 as an anhydrous rhodium alum. Since then, however, true rhodium alums have been obtained. 

Caesium Rhodium Alum, Cs2S04. Rh2(S04)3.24H20, is the most readily prepared of all the rhodium alums on account of its sparing solubility in cold water. The salt crystallises in small yellow octahedra which melt at 110° to 111° C. to a yellowish red liquid. When warmed in a desiccator it loses water, remaining yellow at 100° C., becoming yellowish red at 150° to 180° C., and brown up to 250° C., when it is almost entirely anhydrous. 

Caesium. Iridium Alum, Cs2S04. Ira(S04)3.24H20, yields bright yellow, octahedral crystals, melting at 109 to 110° C. to a yellowish red liquid. Its aqueous solution is yellow, becoming rose-coloured on warming above 40° C. The crystals become anhydrous at 300° to 350° C. 

Ferric Compounds. The hydrated ferric ion, Fe(H20)g+ + +, is pale violet in color. The ion loses protons very readily, however, and ferric salts in solution usually are yellow or brown, because of the formation of hydroxide complexes. Ferric nitrate, Fe(N03)3 6H20, exists as pale violet deliquescent crystals. Anhydrous ferric sulfate, Fe2(S04)g, is obtained as a white powder by evaporation of a ferric sulfate solution. A well-crystallized ferric sulfate is iron alum, KFe(S04)2 12H20, which forms pale violet octahedral crystals. 

At ordinary temperatures, over concentrated sulphuric acid, chrome alum loses 12H2O on heating to 300° to 350° C. it becomes anhydrous, but decomposes in the air. If heated much above 350° C. the residue is then insoluble in vrater. ... 

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