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 Y
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
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
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 (ΔfG˚)	-1232 kJ/mol
Hazards
Safety data sheet	ICSC 1370
EU classification (DSD)	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	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).
N  (what is YN ?)
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.

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

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. 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). Subsequent to its formation, the chromate salt is converted to sodium dichromate, the precursor to most chromium compounds and materials. The industrial route to chromium(III) oxide involves reduction of sodium chromate with sulfur.

It converts to sodium dichromate when treated with acids:

Further acidification affords chromium trioxide:

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. It is also a dyeing auxiliary in the textile industry and a wood preservative. It is a diagnostic pharmaceutical in determining red blood cell volume.

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