Sodium tellurite is an inorganic tellurium compound with formula Na2TeO3. It is a water-soluble white solid and a weak reducing agent. Sodium tellurite is an intermediate in the extraction of the element, tellurium; it is a product obtained from and is a precursor to tellurium.
Preparation
The main source of tellurium is from copper
anode slimes, which contain
as well as various tellurides. These slimes are roasted with
sodium carbonate and oxygen to produce sodium tellurite.
- Ag2Te + Na2CO3 + O2 → 2Ag + Na2TeO3 + CO2 (400–500 °C)
This is a reaction with silver telluride. The telluride is oxidized to tellurite and the silver(I) is reduced to silver.
Purification
The
electrolysis of a tellurite solution yields purified tellurium.
- Anode: 4OH− → 2H2O + O2 + 4e−
- Cathode: TeO32− + 3H2O + 4e− → Te + 6OH−
Structure and properties
Tellurium has properties similar to sulfur and selenium. In the anhydrous form Na
2TeO
3 the tellurium atoms are 6 coordinate, three Te-O at 1.87
Angstroms and three at 2.9
Angstroms, with distorted octahedra sharing edges.
In the pentahydrate, Na
2TeO
3.5H
2O there are discrete tellurite anions, TeO
32− which are pyramidal. The Te-O distance is 1.85 - 1.86
Angstroms and the O-Te-O angle is close to 99.5°.
The tellurite anion is a weak base. Sodium tellurite would be similar to
sodium selenite and
sodium sulfite. Sodium tellurite is both a weak oxidizing agent and a weak reducing agent.
Tellurite-related reactions
- H2TeO3 → H+ + HTeO3− pK 2.48
Telluric acid loses a proton at this pKa.
- HTeO3− → H+ + TeO32− pK 7.7
Hydrogen tellurite loses a proton at this pKa to become the tellurite ion. This would happen in the reaction of tellurous acid with sodium hydroxide to make sodium tellurite.
- TeO2 + 2OH− → TeO32− + H2O
This is the reaction of tellurium dioxide with a base to make a tellurite salt.
Applications
Sodium tellurite improves the corrosion resistance of electroplated nickel layers. Solutions of sodium tellurite are used for black or blue-black coatings on iron, steel, aluminum, and copper. In microbiology, sodium tellurite can be added to the growth medium to isolate bacteria with an inherent physiological resistance to its toxicity.
[Borsetti, Francesca; Toninello, Antonio; Zannoni, Davide (2003). "Tellurite uptake by cells of the facultative phototroph Rhodobacter capsulatus is a pH-dependent process." Federation of European Biochemical Societies. Volume 554, Issue 3, 20 November 2003, pp. 315–318. Elsevier B.V. ]
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Cameo Chemicals. Sodium Tellurite. Retrieved March 8, 2009. Website: http://cameochemical.noaa.gov/chemical/5185.
