Sodium chromate

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Sodium chromate
Sodium-chromate.svg
Chroman sodný.JPG
Names
IUPAC name
Sodium chromate
Other names
Chromic acid, (Na2CrO4), disodium salt
Chromium disodium oxide
Rachromate
Identifiers
  • 7775-11-3 checkY
3D model (JSmol)
ChEBI
ECHA InfoCard 100.028.990 Edit this at Wikidata
EC Number
  • 231-889-5
RTECS number
  • GB2955000
UNII
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)
+55.0·10−6 cm3/mol
Structure
orthorhombic (hexagonal above 413 °C)
Thermochemistry
142.1 J/mol K
174.5 J/mol K
Std enthalpy of
formation (ΔfH⦵298)
 −1329 kJ/mol
Gibbs free energy (ΔfG˚)
 -1232 kJ/mol
Hazards
Safety data sheet ICSC 1370
EU classification (DSD) (outdated)
 Carc. Cat. 2
Muta. Cat. 2
Repr. Cat. 2
Very toxic (T+)
Harmful (Xn)
Corrosive (C)
Dangerous for the environment (N)
R-phrases (outdated) R45, R46, R60, R61, R21, R25, R26, R34, R42/43, R48/23, R50/53
S-phrases (outdated) S53, S45, S60, S61
NFPA 704 (fire diamond)
3
0
OX
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  (what is checkY☒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.

Production and reactivity[]

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

2Cr2O3 + 4 Na2CO3 + 3 O2 → 4 Na2CrO4 + 4 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.[1] 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).[2] Subsequent to its formation, the chromate salt is converted to sodium dichromate, the precursor to most chromium compounds and materials.[3] 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.[3] It is also a dyeing auxiliary in the textile industry.[3] It is a diagnostic pharmaceutical in determining red blood cell volume.[4]

In organic chemistry, sodium chromate is used as an oxidant, converting primary alcohols to carboxylic acids and secondary alcohols to ketones.[5]

See also[]

Safety[]

As with other Cr(VI) compounds, sodium chromate is carcinogenic.[6] The compound is also corrosive and exposure may produce severe eye damage or blindness.[7] Human exposure further encompasses impaired fertility, heritable genetic damage and harm to unborn children.

References[]

  1. ^ "IARC Monographs 49 Ch. 2" (PDF).
  2. ^ Zhi Sun, Yi Zhang, Shi-Li Zheng, Yang Zhang (2009). "A new method of potassium chromate production from chromite and KOH-KNO3-H2O binary submolten salt system". AIChE Journal. 55 (10): 2646–2656. doi:10.1002/aic.11871.CS1 maint: multiple names: authors list (link)
  3. ^ Jump up to: a b c Gerd Anger, Jost Halstenberg, Klaus Hochgeschwender, Christoph Scherhag, Ulrich Korallus, Herbert Knopf, Peter Schmidt, Manfred Ohlinger. "Chromium Compounds". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a07_067.CS1 maint: multiple names: authors list (link)
  4. ^ Bracco Diagnostics Inc. "chromitope sodium (Sodium Chromate, Cr 51) injection, solution". DailyMed. Retrieved 2008-06-20.
  5. ^ Louis F. Fieser "Δ4-cholesten-3,6-dione" Org. Synth. 1955, 35, 36. doi:10.15227/orgsyn.035.0036
  6. ^ IARC (2012) [17-24 March 2009]. Volume 100C: Arsenic, Metals, Fibres, and Dusts (PDF). Lyon: International Agency for Research on Cancer. ISBN 978-92-832-0135-9. Retrieved 2020-01-05. There is sufficient evidence in humans for the carcinogenicity of chromium (VI) compounds. Chromium (VI) compounds cause cancer of the lung. Also positive associations have been observed between exposure to Chromium (VI) compounds and cancer of the nose and nasal sinuses. There is sufficient evidence in experimental animals for the carcinogenicity of chromium (VI) compounds. Chromium (VI) compounds are carcinogenic to humans (Group 1).
  7. ^ "Potassium dichromate MSDS". JT Baker.

Further reading[]

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