Exercise 47. Potassium Hydrogen Pyroantimonate

EXERCISE 47. POTASSIUM HYDROGEN PYROANTIMONATE, K2H2Sb207-4H20 

The salt is very slowly soluble in water, and its solution at once produces a precipitate with sodium salts. It is one of the very few reagents which give such a test for sodium. 

An impure sample of potassium ferrate, K2Fe04, may be prepared as follows Dissolve sufficient ferric chloride, FeCl3,6H20, to correspond to 40 g. Fe(OH)3 in 2 1. of hot water and precipitate the hydroxide with potassium hydroxide. Wash the precipitate repeatedly with hot water by decantation until nearly all chlorides have been removed and evaporate the suspended hydroxide to a volume of about 65 cc., bringing it into a porcelain dish that will hold about 250 cc. Break up 25 g. of solid potassium hydroxide into small pieces and add it to the ferric hydroxide, warming the mixture to insure solution. 

The solid may be filtered off on a filter of glass wool or asbestos, washed repeatedly with 96 per cent alcohol to remove KOH, dried, and preserved. It is not easy to purify this preparation from other potassium salts. 

Barium ferrate, BaFe04, like barium sulfate and barium chromate, is insoluble and is the most stable of the ferrates. Dissolve the potassium salt in about ten times its weight of water, filter it through a filter paper 

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