Ammonium vanadium alum

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... 

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 ... 

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]. 

Piccini was obsessed with studying the limiting form of the elements as placed in the periodic table. With this in mind, he took up a new field of research, the synthesis of double sulfates (or alums), a work that enormously stimulated his creativity and enthusiasm [58]. In rapid succession, he prepared the alums of vanadium [59], titanium [60, 61], rhodium [62], manganese [63], iridium, and, finally, of thallium [64] with ammonium and then with the following alkaline metals cesium, mbidium, and potassium. Piccini ably used his method of synthesizing the rhodium sulfates virtually to quantitatively separate rhodium from iridium in solution. Through successive fractional crystallizations, Piccini obtained the alums of rhodium and cesium free of iridium, and through electrolysis of the alums he was able to obtain pure rhodium. 

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