Sodium chromate
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Template:Chembox image cellTemplate:Chembox image cellTemplate:Chembox AllOtherNamesTemplate:Chembox headerbarTemplate:Chembox IndexlistTemplate:Chembox JmolTemplate:Chembox ChEMBLTemplate:Chembox ECHATemplate:Chembox E numberTemplate:Chembox IUPHAR ligandTemplate:Chembox UNIITemplate:Chembox CompToxTemplate:Chembox headerbarTemplate:Chembox SolubilityInWaterTemplate:Chembox headerbarTemplate:Chembox headerbarTemplate:Chembox DeltaGfreeTemplate:Chembox HazardsTemplate:Chembox headerbarTemplate:Chembox Datapage checkTemplate:Yesno| Template:Longitem | Template:Unbulleted list |
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| UN number | 3288 |
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| Template:Longitem | Na2CrO4 |
| Molar mass | 161.97 g/mol |
| Appearance | yellow crystals |
| Odor | odorless |
| Density | 2.698 g/cm3 |
| Melting point | Template:Chembox CalcTemperatures |
| Solubility | slightly soluble in ethanol |
| Solubility in methanol | 0.344 g/100 mL (25 °C) |
| Template:Longitem | +55.0·10−6 cm3/mol |
| Template:Longitem | orthorhombic (hexagonal above 413 °C) |
| Template:Longitem | 142.1 J/mol K |
| Template:Longitem | 174.5 J/mol K |
| Template:Longitem | −1329 kJ/mol |
| Template:Longitem | Sodium dichromate Sodium molybdate Sodium tungstate |
| Template:Longitem | Potassium chromate Calcium chromate Barium chromate |
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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
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- ↑ a b c Template:Ullmann
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- ↑ Louis F. Fieser "Δ4-cholesten-3,6-dione" Org. Synth. 1955, 35, 36. Script error: No such module "CS1 identifiers".
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Further reading
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- Record of Sodium chromate in the GESTIS Substance Database of the Institute for Occupational Safety and HealthScript error: No such module "TemplatePar".
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