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Sodium chromate

Chromium disodium oxide Rachromate 20 °C (decahydrate) 84.5 g/100 mL (25 °C) 126.7 g/100 mL (100 °C) | NFPA-H = 3 | NFPA-F = 0 | NFPA-R = | NFPA-S = OX Calcium chromate Barium chromate Sodium molybdate Sodium tungstate

Sodium chromate is the inorganic compound with the formula Na2CrO4. It is 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. 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.

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. It is also a dyeing auxiliary in the textile industry.

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

Safety

As with other Cr(VI) compounds, sodium chromate is carcinogenic.{{cite book |author-link = International Agency for Research on Cancer |orig-year = 17-24 March 2009 |access-date = 2020-01-05 |archive-date = 2020-03-17 |archive-url = https://web.archive.org/web/20200317095517/https://publications.iarc.fr/_publications/media/download/3026/50ed50733f7d1152d91b30a803619022ef098d59.pdf |url-status = dead

References

References

  1. "IARC Monographs 49 Ch. 2".
  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.
  3. Gerd Anger, Jost Halstenberg, Klaus Hochgeschwender, Christoph Scherhag, Ulrich Korallus, Herbert Knopf, Peter Schmidt, Manfred Ohlinger. "Chromium Compounds".
  4. Bracco Diagnostics Inc.. "chromitope sodium (Sodium Chromate, Cr 51) injection, solution". DailyMed.
  5. [[Louis F. Fieser]] "Δ4-cholesten-3,6-dione" Org. Synth. 1955, 35, 36. {{doi. 10.15227/orgsyn.035.0036
  6. "Potassium dichromate MSDS". JT Baker.
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chromates sodium-compounds oxidizing-agents
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