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
ChEBI	CHEBI:78671 N
EC Number	231-889-5
Jmol 3D model	Interactive image
PubChem	24488
RTECS number	GB2955000
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)
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
Vapor pressure	{{{value}}}
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 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.

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. 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.

Acid-base behavior

It converts to sodium dichromate when treated with acids:

2 Na₂CrO₄ + 2 H+ → + H₂O + Na₂Cr₂O₇

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. 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.

See also

• Chromate

Further reading

• Record of Sodium chromate in the GESTIS Substance Database of the IFA