STRONTIUM SELENITE

Description

Strontium selenite has the molecular formula of SrSeO3 and the molecular weight of 214.5782 g/mol. It can be prepared by adding strontium hydroxide or carbonate to selenous acid which has been stabilized by sodium carbonate to form the sodium salt:
Sr(OH)2(solid)+ Na2SeO3(aq)
? SrSeO3·7H2O(solid)+H2O
The product is a heptahydrate whose CAS number is 14590-38-6. This compound is insoluble in water but soluble in dilute acids. An acid selenite, Sr(HSeO3)2, has been reported that is soluble in water. However, its existence has not been confirmed. If it exists, it would be obtained by low temperature evaporation of the solution at an acid pH (～pH=5.5) and would probably require the presence of ammonium hydroxide during the evaporation to form the crystals. The existence of a hydrate remains unknown.

Preparation

A solution of 77 g of sublimed selenium(1V) 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-ml portions of hot distilled water. The nitrate content should be less than 5 parts per million as determined by the diphenylaminesulfuric acid test. The strontium selenite is dried at 200°C for several hours. The yield is about 125 g.
During synthesis of the monazite-type strontium selenate, SrSeO4, a new compound SrSe2O5 was obtained. This compound was formed by the reaction of hydrogen peroxide upon a mixture of strontium oxide plus selenous acid at a 1:2 molar ratio:
2SrO+ 4H2SeO3+ 2H2O2?2SrSe2O5+ 6H2O+ O2