Preparation of Strontium Compounds

Strontium Nitrate. In the procedure that follows, the concentration of barium ion is lessened by precipitation as the sulfate ammonium oxalate is employed to reduce 

From 1 to 1.8 ml. of distilled nitric acid is next added to the filtrate to lower the pH to about 2 upon boiling the solution, a deposit of sulfur is obtained. After standing for several hours this is removed by filtration. 

The resulting strontium nitrate solution is now concentrated by evaporation until bumping commences. It is cooled and nitric acid distilled into the solution until precipitation ceases. The supernatant liquid is removed as completely as possible, emplo3dng the technique shown in Fig. 6. The crystalline mass is dissolved in the smallest possible quantity of doubly distilled water and the solution is filtered. The crystallization procedure is repeated twice, yielding as the final product a saturated solution of thrice recrystallized strontium nitrate. This solution is diluted to 500 ml. with doubly distilled water and is used for the precipitation of strontium sulfate or strontium selenite. 

Strontium Sulfate. The 500 ml. of strontium nitrate solution is heated to boiling in a round-bottomed flask and strontium sulfate is precipitated by the slow addition of a solution of 50 ml. of reagent-grade sulfuric acid (36 N) in 65 ml. of distilled water. When the precipitate has settled, the supernatant liquid is removed by the inverted filtration technique and the precipitate washed successively with five 200-ml. portions of hot, doubly distilled water. For the last washing the precipitate should be transferred to a beaker. It may then be removed more easily after drying for several hours at 200°. The strontium sulfate should not contain more than 20 parts per million of nitrate ion using diphenylamine-sulfuric acid reagent as a colorimetric test. The yield is about 120 g.  

Strontium Selenite. A solution of 77 g. of sublimed selenium(IV) oxide in 154 ml. of distilled water is added to 500 ml. of pure strontium nitrate solution prepared as previously described. The solution is heated to boiling and fresh ammonium hydroxide solution is added until no further precipitation of strontium selenite occurs. The precipitate is drained and washed six times with 300-mI. portions of hot distilled water. The nitrate content should be less than 5 parts per million as determined by the diphenylamine-sulfuric acid test. The strontium selenite is dried at 200° for several hours. The yield is about 125 g. 

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