Sodium chromate
Chemical compound From Wikipedia, the free encyclopedia
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.
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| Names | |
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| IUPAC name
Sodium chromate | |
| Other names
Chromic acid, (Na2CrO4), disodium salt Chromium disodium oxide Rachromate | |
| Identifiers | |
3D model (JSmol) |
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| ChEBI | |
| ChemSpider | |
| ECHA InfoCard | 100.028.990 |
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PubChem CID |
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| UNII | |
| UN number | 3288 |
CompTox Dashboard (EPA) |
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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) |
142.1 J/mol K |
Std molar entropy (S⦵298) |
174.5 J/mol K |
Std enthalpy of formation (ΔfH⦵298) |
−1329 kJ/mol |
Gibbs free energy (ΔfG⦵) |
−1232 kJ/mol |
| Hazards | |
| GHS labelling: | |
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| 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+P310, P301+P330+P331, P302+P352, P303+P361+P353, P304+P340, P304+P341, P305+P351+P338, P308+P313, P310, P312, P314, P320, P321, P322, P330, P333+P313, P342+P311, P363, P391, P403+P233, P405, P501 | |
| NFPA 704 (fire diamond) | |
| Flash point | Non-flammable |
| Safety data sheet (SDS) | ICSC 1370 |
| 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).
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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
Further reading
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