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Sodium chromate

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] Sodium chromate is a strong oxidizer.

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.

See also

References

  1. ^ IARC Monographs 49 Ch. 2 (PDF). ISBN 9789283212492.
  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.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  3. ^ 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. ISBN 978-3527306732.{{cite encyclopedia}}: 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. Archived from the original (PDF) on 2020-03-17. 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