Potassium metavanadate, preparation

Prepare 10 g. of potassium metavanadate, KVO 3, either by heating a solution of vanadium pentoxide, V2O5, with the necessary amount of a solution of potassium hydroxide or by boiling the necessary amount of ammonium metavanadate (difficultly soluble) with the required quantity of potassium hydroxide. In either case, obtain the white, needle-shaped crystals by evaporation. 

Calcium Metavanadate, Ca(V03)2.3H20, gives rise to bright yellow needles when a solution of ammonium metavanadate is boiled with calcium chloride solution and precipitated with alcohol.6 The tetra-hydrate, Ca(V03)2.4H20, is prepared by allowing a mixture of potassium metavanadate and calcium chloride to evaporate for several days.7 Anhydrous calcium metavanadate is a white, porous substance, which is unaffected by strong heating, but is readily decomposed by acids to yield vanadium pentoxide.8 It is much more soluble in water than strontium metavanadate. 

At a pH near 6, manganese(II) metavanadate precipitates and does not react further, whereas at a pH near 2, other heteropoly species are formed. Inasmuch as commercial potassium metavanadate is not suitable for the syntheses of the 13-vanadomanganate(IV) and nickelate(IV), directions for the preparation of this compound are included in the syntheses below, which are modified from the method of Flynn and Pope.5 The preparation of the yellow-tinged green reduced form of potassium 13-vanadomanganate(IV) is also included.5... 

Catalyst is prepared by mixing a silica sol made from potassium silicate with vanadyl sulfate or anunonia metavanadate and precipitating with ammonia. The silica used can be either fresh or a soUd sueh as kieselguhr. A sol mixed with... 

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