Sodium Selenate --- Na2O4Se and Sodium Selenite --- Na2SeO3 are two different compounds, often confused by purchasers.
Ph Eur
Na2SeO3,5H2O -- 263.0 -- 26970-82-1
DEFINITION
Content: 98.5 per cent to 101.5 per cent.
CHARACTERS
Appearance: White or almost white, crystalline powder, hygroscopic.
Solubility: Freely soluble in water, practically insoluble in ethanol (96 per cent).
IDENTIFICATION
A. Dissolve 50 mg in 5 ml of a mixture of equal volumes of dilute hydrochloric acid and water and heat to boiling. Add 0.05 g of ascorbic acid; a red precipitate is formed which may become black.
B. Dissolve 50 mg in a mixture of 1 ml of dilute hydrochloric acid and 5 ml of water. Add 1 ml of barium chloride solution; the solution remains clear.
C. It gives reaction of sodium.
D. It complies with the limits of the assay.
TESTS
Solution S: Dissolve 5.0 g in carbon dioxide-free water and dilute to 50.0 ml with the same solvent.
Appearance of solution: Solution S is clear and colourless.
pH: 9.8 to 10.8 for solution S.
Chlorides: Maximum 50 ppm.
Sulphates and selenates: Maximum 300 ppm (determined as sulphates).
Iron: Maximum 50 ppm.
