Sodium selenite

Sodium selenate (IV )

Colorless and odorless, moisture- sensitive powder

Fixed

3.4 g · cm -3

320 ° C ( decomposition)

Well in water (950 g · l-1 at 20 ° C)

Risk

0.05 mg · m-3

7 mg · kg -1 ( LD50, rat, oral)

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Sodium is the sodium salt of selenious acid ( H2SeO3 ) with the chemical formula Na2SeO3. It is in the form of needle-shaped, white, hygroscopic crystals before.

Occurrence

Sodium occurs naturally in animal tissues.

Production and representation

The salt can be recovered by dissolving selenium dioxide in sodium hydroxide solution, the resulting reaction by the Selendioxids with water selenious acid reacts with sodium hydroxide to sodium selenite:

Net reaction:

Properties

Physical Properties

Sodium selenite is a colorless, odorless, moisture- sensitive solid. It has a monoclinic crystal structure with space group P21 / a

The standard enthalpy of formation for solid sodium selenite is -959 kJ / mol for the anhydrous salt or at -2404 kJ / mol for the pentahydrate.

The selenite ion is built pyramidal with C3v symmetry, the distance between oxygen and selenium atom is 1.74 Å.

At about 40 ° C the pentahydrate gives off its water of crystallization.

Chemical Properties

From sodium selenite very easy red amorphous selenium is cleaved by reducing agents.

Use

Sodium selenite ( reduction to red selenium ), as part of fixing baths and for testing the germination of seeds is used to red coloration of glass and porcelain. Furthermore, it is in very low concentration ( 50-1000 micrograms ) used in medicine in selenium deficiency ( Keshan disease ) in cancer therapy and as an additive in animal nutrition. It's also used as a detection reagent for alkaloids.

In Sweden embedded sodium selenite for the precipitation of mercury ions is used as an insoluble mercury selenide in lakes in plastic.

Safety

Sodium selenite is highly toxic, in category 3B (suspected carcinogenic effect ) with respect to carcinogenic effects, and in the category C (no risk in compliance with the limit values) classified with respect to embryo damage.