Sodium chromate

Sodium chromate
Names
	IUPAC name Sodium chromate
	Other names Chromic acid, (Na2CrO4), disodium salt; Chromium disodium oxide; Rachromate
Identifiers
CAS Number	7775-11-3 ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:78671 ;
ECHA InfoCard	100.028.990
EC Number	231-889-5;
PubChem CID	24488;
RTECS number	GB2955000;
UNII	6A49BO6K4M ;
UN number	3288
CompTox Dashboard (EPA)	DTXSID7032056 ;
	InChI InChI=1S/Cr.2Na.4O/q;2+1;;;2-1;
	SMILES [O-][Cr](=O)(=O)[O-].[Na+].[Na+];
Properties
Chemical 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)
Magnetic susceptibility (χ)	+55.0·10−6 cm3/mol
Structure
Crystal structure	orthorhombic (hexagonal above 413 °C)
Thermochemistry
Heat capacity (C)	142.1 J/mol K
Std molar; entropy (So298)	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EU classification (DSD) (outdated)	Carc.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R-phrases (outdated)	R45, R46, R60, R61, R21, R25, R26, R34, R42/43, R48/23, R50/53
S-phrases (outdated)	S53, S45, S60, S61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)	0 3 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).
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	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]

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

"IARC Monographs 49 Ch. 2" (PDF).
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)
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)
Bracco Diagnostics Inc. "chromitope sodium (Sodium Chromate, Cr 51) injection, solution". DailyMed. Retrieved 2008-06-20.
Louis F. Fieser "Δ⁴-cholesten-3,6-dione" Org. Synth. 1955, 35, 36. doi:10.15227/orgsyn.035.0036
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).
"Potassium dichromate MSDS". JT Baker.