Chemistry:Sodium chromate
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| Names | |
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| IUPAC name
Sodium chromate
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| Other names
Chromic acid, (Na2CrO4), disodium salt
Chromium disodium oxide Rachromate | |
| Identifiers | |
3D model (JSmol)
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| ChEBI | |
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| EC Number |
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PubChem CID
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| RTECS number |
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| UNII | |
| UN number | 3288 |
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| 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) |
| +55.0·10−6 cm3/mol | |
| Structure | |
| orthorhombic (hexagonal above 413 °C) | |
| Thermochemistry | |
Heat capacity (C)
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142.1 J/mol K |
Std molar
entropy (S |
174.5 J/mol K |
Std enthalpy of
formation (ΔfH⦵298) |
−1329 kJ/mol |
Gibbs free energy (ΔfG˚)
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-1232 kJ/mol |
| Hazards | |
| Safety data sheet | ICSC 1370 |
| GHS pictograms |     
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| GHS Signal word | Danger |
| H301, H312, H314, H317, H330, H334, H340, H350, H360, H372, H410 | |
| P201, P202, P260, P261, P264, P270, P271, P272, P273, P280, P281, P284, P285, P301+310, P301+330+331, P302+352, P303+361+353, P304+340, P304+341, P305+351+338, P308+313, P310, P312, P314, P320 | |
| NFPA 704 (fire diamond) | |
| Flash point | Non-flammable |
| Related compounds | |
Other anions
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Sodium dichromate Sodium molybdate Sodium tungstate |
Other cations
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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). | |
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| 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.
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.
See also
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.
References
- ↑ IARC Monographs 49 Ch. 2. ISBN 9789283212492. https://monographs.iarc.fr/ENG/Monographs/vol49/mono49-6B.pdf.
- ↑ 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.
- ↑ 3.0 3.1 3.2 Gerd Anger, Jost Halstenberg, Klaus Hochgeschwender, Christoph Scherhag, Ulrich Korallus, Herbert Knopf, Peter Schmidt, Manfred Ohlinger. "Ullmann's Encyclopedia of Industrial Chemistry". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a07_067.
- ↑ Bracco Diagnostics Inc.. "chromitope sodium (Sodium Chromate, Cr 51) injection, solution". DailyMed. http://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?id=6525.
- ↑ Louis F. Fieser "Δ4-cholesten-3,6-dione" Org. Synth. 1955, 35, 36. doi:10.15227/orgsyn.035.0036
- ↑ IARC (2012). Volume 100C: Arsenic, Metals, Fibres, and Dusts. Lyon: International Agency for Research on Cancer. ISBN 978-92-832-0135-9. https://publications.iarc.fr/_publications/media/download/3026/50ed50733f7d1152d91b30a803619022ef098d59.pdf. 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)."
- ↑ "Potassium dichromate MSDS". JT Baker. http://hazard.com/msds/mf/baker/baker/files/p5719.htm.
Further reading
- "Sodium chromate". inchem. http://www.inchem.org/documents/icsc/icsc/eics1370.htm.
- Record of Sodium chromate in the GESTIS Substance Database of the Institute for Occupational Safety and Health
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