Sodium tellurite

Sodium tellurite
Other names Sodium Tellurite IV, Tellurous acid disodium salt
Identifiers
CAS number	10102-20-2
PubChem	24935
ChemSpider	23309 Y
RTECS number	WY2450000
Jmol-3D images	Image 1
SMILES [Na+].[Na+].[O-][Te]([O-])=O
InChI InChI=1S/2Na.H2O3Te/c;;1-4(2)3/h;;(H2,1,2,3)/q2*+1;/p-2 Y Key: VOADVZVYWFSHSM-UHFFFAOYSA-L Y InChI=1/2Na.H2O3Te/c;;1-4(2)3/h;;(H2,1,2,3)/q2*+1;/p-2 Key: VOADVZVYWFSHSM-NUQVWONBAS
Properties
Molecular formula	Na2TeO3
Molar mass	221.57774 g/mol
Appearance	white crystals, powder
Density	6.245 g/cm3
Melting point	710 °C
Boiling point	unknown (very high)
Solubility in water	soluble greater than or equal to 100 mg/mL at 68°F
Hazards
R-phrases	R23 R24 R25
S-phrases	S22 S36 S37 S39 S45
Flash point	?°C
Y tellurite (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

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 mineral obtained from slimes and is a precursor to tellurium.

Preparation

The main source of tellurium is from copper anode slimes, which contain precious metals as well as various tellurides. These slimes are roasted with sodium carbonate and oxygen to produce sodium tellurite^[1].

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^[1].

Anode: 4OH^– → 2H₂O + O₂ + 4e^–

Cathode: TeO₃^2– + 3H₂O + 4e^– → Te + 6OH^–

Structure and properties

Tellurium has properties similar to sulfur and selenium. The tellurite anion is pyramidal with C_3v symmetry. The Te-O distance is 1.86 Å and the O-Te-O angle is 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⁺ + TeO₃^2– 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^– → TeO₃^2– + 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.^[2]

References

1. ^ ^{a b} Wiberg, Egon; Holleman, Arnold Frederick (2001). Nils Wiberg. ed. Inorganic chemistry. Academic Press. p. 588. ISBN 0-12-352651-5. 
2. ^ 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. doi:10.1016/S0014-5793(03)01180-3

• Cameo Chemicals. Sodium Tellurite. Retrieved March 8, 2009. Website: http://cameochemical.noaa.gov/chemical/5185.
• Knockaert, Guy (2000, June). Copyright © 2002 by Wiley-VCH Verlag GmbH & Co. KGaA. All rights reserved. Retrieved March 8, 2009. Website: http://mrw.interscience.wiley.com. proxy2.library.uiuc.edu/emrw/9783527306732/ueic/article/a26_177/current/pdf.
• Safety data for sodium tellurite. (2008) Retrieved March 8, 2009. Website: http://msds.chem.ox.ac.uk/SO/sodium_tellurite.html.
• Acta Crystallographica Section B "Etude cristallographique du tellurite de sodium à cinq molécules d'eau, Na2TeIVO3.5H2O" Volume 35 1979 p 1337-1340. DOI: 10.1107/S0567740879006403.