Exercise 82. Barium Dithionate

The preparation of this salt depends upon the preparation of manganese dithionate according to the equation 

The more finely divided the manganese dioxide the more rapid will be the reaction, so that the precipitated reagent is better than finely powdered pyrolusite. It is still better to prepare the precipitated hydroxide Mn(OH)4, by reducing the necessary quantity of potassium permanganate in neutral solution with alcohol and washing the precipitate from soluble potassium salts by decantation. 

Saturate about 250 cc. of water with sulfur dioxide. The dioxide is most conveniently prepared by placing 150 g. of sodium sulfite in a flask, adding enough water to cover it, and slowly dropping into the flask through a separatory funnel concentrated sulfuric acid. Cool 

This reaction is favored by high temperatures. Does this equation suggest why the manganese dioxide is added to the sulfur dioxide rather than the reverse  

Pass carbon dioxide through the filtrate until all excess of barium hydroxide has been precipitated as carbonate filter and evaporate to crystallization. Other dithio-nates can be prepared from the barium salt by double decomposition with sulfates of other metals. 

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The procedure used in the preparation of calcium dithionate is followed except that barium hydroxide is employed instead of calcium hydroxide. For the amounts specified for calcium dithionate, the initial quantity of barium hydroxide, Ba(OH)2 8H20, should be about 160 g. Because of the greater solubility of barium hydroxide, greater care must be exercised in arriving at the end point (strong alkalinity to litmus paper). 

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