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Sodium chromate

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Sodium chromate

Sodium chromate
Names
IUPAC name
Sodium chromate
Other names
Chromic acid, (Na2CrO4), disodium salt
Chromium disodium oxide
Rachromate
Identifiers
 YesY
ChEBI  N
EC number 231-889-5
Jmol-3D images Image
PubChem
RTECS number GB2955000
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 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  (: YesY/N?)

Sodium chromate is the hydrates. 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. 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 + 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.[1] It is also a dyeing auxiliary in the textile industry[1] and a wood preservative.[2] It is a diagnostic pharmaceutical in determining red blood cell volume.[3]

In organic chemistry, sodium chromate is used as an oxidant, converting primary alcohols to carboxylic acids and secondary alcohols to ketones.[4]

See also

References

  1. ^ a b c d
  2. ^
  3. ^
  4. ^ doi:10.15227/orgsyn.035.0036

Further reading

  • Sodium chromateRecord of in the GESTIS Substance Database of the IFA


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