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
