Vanadium alums

Vanadium II) forms green V2(S04)3 (electrolytic or Mg reduction of V2O5 in H2SO4). Alums and other double salts are formed. 

Values for the formation constants of [V(C204)]+ and [V(C204)2] were respectively 1.6 x 107 and 3.5 x 1012.271 By irradiation of these solutions at 254 nm, there is a photodecomposition of the oxalate sensitized by the oxalato vanadium(III) complex the resulting products were equimolar amounts of CO and C02. K3[V(C204)3]-3H20 can be easily crystallized from aqueous solutions containing ammonium vanadium alum and potassium oxalate. The measured magnetic moment is 2.78 BM and this compound obeys the Curie law quite closely.272 The thermal decomposition has been studied.273... 

Alum, KAl(S0i)i-l2H20.—Ammonium, rubidium, cesium, univalent thallium, and in some cases sodium may replace potassium, while the aluminum may be replaced by trivalent iron, chromium, indium, gallium, titanium, vanadium but not by the rare-earth metals. 

Biiltemann 2 observed that vanadium ammonium alum separates out in blue crystals from a solution containing sulphuric acid, but from solutions containing a weak acid, or from neutral solutions, red crystals are obtained. (The chromium alums can also be prepared in differently coloured modifications.) The analytical data, melting-point, electrical conductivity, rate of efflorescence, and general behaviour of both kinds of crystals are identical, so that it is difficult to ascribe different constitutions to them. Meyer and Markowitz3 have shown that both forms separate out when the molecular proportion of sulphuric acid in the solution is less than that theoretically required, and attribute the red colour to the presence of traces of vanadous oxide, V203, or its hydroxide, V(OH)3. Vanadium rubidium and vanadium ciesium alums behave in the same way. A vanadium guanidine alum has also been prepared.4... 

The general constitutional formula for the vanadium alums is [V(H402)6](S04)(S04R), which differs from the formulas for other double vanadium sulphates in that the sulphato groups are not attached to the nuclear vanadium atom. 

Vanadyl Selenite, V02.Se02.2H20, is obtained in blue, microscopic crystals when the hydrate of hypovanadic oxide, V02.2Ha0, is dissolved in an aqueous solution of selenous acid and the solution evaporated.3 Efforts to prepare normal selenates and selenate alums of trivalent vanadium were unsuccessful, but several hydrated aceto-selenates of trivalent vanadium have been isolated.4... 

Vanadous Pyrophosphate, V4(P2O7)2.30H2O, is obtained as a green, floceulent predpitate when vanadium ammonium alum is added to a solution of an alkaline pyrophosphate.3... 

The only simple sulfates of vanadium are formed in the oxidation states -1-3 and -1-2. Vanadium(III) sulfate can be crystallized as a hydrate from aqueous solution, and is strongly reducing. It gives rise to a series of alums of the type M V(S04)2-12H20, which have been shown to contain the [V(H206)] + ion. The ammonium alum, (NH4)V(S04)2 12H20, is obtained as air-stable blue violet crystals by electrolytic reduction of NH4[V03] in sulfuric acid.b ... 

The chromous salts, derived from the oxide CrO, arc analogous to the salts of divalent vanadium, manganese, and iron. This is seen in the isomorphism of the sulphates of the type R" SOj-THgO. The stability of such salts increases in the order of the atomic number of the metal. The chief basic oxide of chromium is the sesquioxidc CraO, which is closely allied to ferric oxide, and, like the latter, resembles aluminium oxide. The hydroxide, Cr(OH)3, with bases yields chromites analogous to, but less stable than, the aluminates. Chromic sulphate enters into the formation of alums. The chromic salts are very stable, but in the trivaJent condition the metal shows a marked tendency to form complex ions, both anions and cations thus it resembles iron in producing complex cyanides, whilst it also yields compounds similar to the cobaltamines. 

Good precision and accuracy were obtained in determinations of trace amounts (10 %) of vanadium in ferri-ammonium and aluminium-ammonium alums by the method with Brilliant Green [33]. 

Solubility of Caesium Chromium Alum, Caesium Iron Alum, Caesium Indium Alum, and of Caesium Vanadium Alum in Water. 

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