Sodium chromate

Sodium chromate
Names
IUPAC name
Sodium chromate
Other names
Chromic acid, (Na2CrO4), disodium salt
Chromium disodium oxide
Rachromate
Identifiers
7775-11-3 YesY
3D model (Jmol) Interactive image
ChEBI CHEBI:78671 N
ECHA InfoCard 100.028.990
EC Number 231-889-5
PubChem 24488
RTECS number GB2955000
UNII 6A49BO6K4M N
UN number 3288
Properties
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)
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
orthorhombic (hexagonal above 413 °C)
Thermochemistry
142.1 J/mol K
174.5 J/mol K
−1329 kJ/mol
-1232 kJ/mol
Hazards
Safety data sheet ICSC 1370
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
0
3
Flash point Non-flammable
Related compounds
Other anions
 Sodium dichromate
Sodium molybdate
Sodium tungstate
Other cations
 Potassium chromate
Calcium chromate
Barium chromate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YesYN ?)
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

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. Typically calcium carbonate is included in the mixture to improve oxygen access and to keep silicon and aluminium impurities in an insoluble form. The process temperature is typically around 1100 C.[2] For lab and small scale preparations a mixture of chromite ore, sodium hydroxide and sodium nitrate reacting at lower temperatures may be used (even 350 C in the corresponding potassium chromate system).[3] 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.

Acid-base behavior

It converts to sodium dichromate when treated with acids:

2 Na2CrO4 + 2HCl → Na2Cr2O7 + 2NaCl + H2O

Further acidification affords chromium trioxide:

Na2CrO4 + H2SO4 → CrO3 + Na2SO4 + H2O

Uses

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.[4] It is a diagnostic pharmaceutical in determining red blood cell volume.[5]

In organic chemistry, sodium chromate is used as an oxidant, converting primary alcohols to carboxylic acids and secondary alcohols to ketones.[6]

See also

References

  1. 1 2 3 4 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. ↑ "IARC Monographs 49 Ch. 2" (PDF).
  3. ↑ Zhi Sun, Yi Zhang, Shi-Li Zheng, Yang Zhang. "A New Method of Potassium Chromate Production from Chromite and KOH-KNO3-H2O Binary Submolten Salt System,AIChE Journal 55(10) (2009) pp 2646-2656". PAN Pesticides Database.
  4. ↑ "Sodium chromate - Pesticide use statistics for 2005". PAN Pesticides Database. Retrieved 2008-06-20.
  5. ↑ Bracco Diagnostics Inc. "chromitope sodium (Sodium Chromate, Cr 51) injection, solution". DailyMed. Retrieved 2008-06-20.
  6. ↑ Louis F. Fieser "Δ4-cholesten-3,6-dione" Org. Synth. 1955, 35, 36. doi:10.15227/orgsyn.035.0036

Further reading

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