Sodium chromate

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Sodium chromate
Sodium-chromate.svg
Chroman sodný.JPG
Identifiers
CAS number 7775-11-3 YesY
PubChem 24488
EC number 231-889-5
UN number 3288
ChEBI CHEBI:78671 N
RTECS number GB2955000
Jmol-3D images Image 1
Properties
Molecular formula Na2CrO4
Molar mass 161.97 g/mol
Appearance yellow crystals
Odor odorless
Density 2.698 g/cm3
Melting point 792 °C (1,458 °F; 1,065 K) (anhydrous)
20 °C (decahydrate)
Solubility in water 31.8 g/100 mL (0 °C)
84.5 g/100 mL (25 °C)
126.7 g/100 mL (100 °C)
Solubility slightly soluble in ethanol
Solubility in methanol 0.344 g/100 mL (25 °C)
Structure
Crystal structure orthorhombic (hexagonal above 413 °C)
Thermochemistry
Specific
heat capacity
C
142.1 J/mol K
Std molar
entropy
So298
174.5 J/mol K
Std enthalpy of
formation
ΔfHo298
−1329 kJ/mol
Gibbs free energy ΔG -1232 kJ/mol
Hazards
MSDS ICSC 1370
EU Index 024-018-00-3
EU classification Carc. Cat. 2
Muta. Cat. 2
Repr. Cat. 2
Very toxic (T+)
Harmful (Xn)
Corrosive (C)
Dangerous for the environment (N)
R-phrases R45, R46, R60, R61, R21, R25, R26, R34, R42/43, R48/23, R50/53
S-phrases S53, S45, S60, S61
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity (yellow): no hazard code Special hazard OX: Oxidizer. E.g., potassium perchlorateNFPA 704 four-colored diamond
Flash point Non-flammable
Related compounds
Other anions Sodium dichromate
Sodium molybdate
Sodium tungstate
Other cations Potassium chromate
Calcium chromate
Barium chromate
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

Sodium chromate is the inorganic compound with the formula Na2CrO4. It exists as a yellow hygroscopic solid, which can form tetra-, hexa-, and decahydrates. It is an intermediate in the extraction of chromium from its ores. Sodium chromate, like other hexavalent chromium compounds, is toxic and carcinogenic.[1]

Production and reactivity[edit]

It is obtained on a vast scale by roasting chromium ores in air in the presence of sodium carbonate:

Cr2O3 + 2 Na2CO3 + 3/2 O2 → 2 Na2CrO4 + 2 CO2

This process converts the chromium into a water-extractable form, leaving behind iron oxides. Subsequent to its formation, the chromate salt is converted to sodium dichromate, the precursor to most chromium compounds and materials.[1] The industrial route to chromium(III) oxide involves reduction of sodium chromate with sulfur.

It is a strong oxidant, capable of converting alcohols to carboxylic acids.

Acid-base behavior[edit]

It can also be obtained by the reaction of sodium dichromate with sodium hydroxide.

Na2Cr2O7 + 2 NaOH → 2 Na2CrO4 + H2O

Acidification affords chromium trioxide:

Na2CrO4 + H2SO4 → CrO3 + Na2SO4 + H2O

Uses[edit]

Aside from its central role in the production of chromium from its ores, sodium chromate is used as a corrosion inhibitor in the petroleum industry.[1] It is also a dyeing auxiliary in the textile industry[1] and a wood preservative.[2] It is a diagnostic pharmaceutical in determining red blood cell volume.[3]

See also[edit]

References[edit]

  1. ^ a b c d Gerd Anger, Jost Halstenberg, Klaus Hochgeschwender, Christoph Scherhag, Ulrich Korallus, Herbert Knopf, Peter Schmidt, Manfred Ohlinger (2005), "Chromium Compounds", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a07_067 
  2. ^ "Sodium chromate - Pesticide use statistics for 2005". PAN Pesticides Database. Retrieved 2008-06-20. 
  3. ^ Bracco Diagnostics Inc. "chromitope sodium (Sodium Chromate, Cr 51) injection, solution". DailyMed. Retrieved 2008-06-20. 

Further reading[edit]