Sodium chromate
Key intermediate in chromium extraction and industrial oxidizer.
Sodium chromate (Na₂CrO₄) is a yellow, hygroscopic solid that exists as tetra-, hexa-, and decahydrates. It is a key intermediate in extracting chromium from its ores. Industrially, it is produced in massive quantities by roasting chromium ores with sodium carbonate in air at around 1100 °C. This reaction converts chromium into a water-soluble form, leaving iron oxides behind; calcium carbonate is often added to improve oxygen flow and keep silicon and aluminum impurities insoluble. For smaller-scale or laboratory work, a mixture of chromite ore, sodium hydroxide, and sodium nitrate can be used at lower temperatures (as low as 350 °C in the analogous potassium chromate system). After formation, the chromate salt is usually converted into sodium dichromate, the precursor for most chromium compounds. The industrial route to chromium(III) oxide involves reducing sodium chromate with sulfur.
When treated with acids, sodium chromate converts to sodium dichromate; further acidification yields chromium trioxide. Beyond its central role in chromium production, it is used as a corrosion inhibitor in the petroleum industry and as a dyeing auxiliary in textiles. In medicine, it serves as a diagnostic agent for measuring red blood cell volume. In organic chemistry, it acts as a strong oxidizer, converting primary alcohols to carboxylic acids and secondary alcohols to ketones.
As a chromium(VI) compound, sodium chromate is carcinogenic. It is also corrosive, and exposure can cause severe eye damage or blindness. Human exposure may also impair fertility, cause heritable genetic damage, and harm unborn children.
- formula
- Na2CrO4
- appearance
- yellow hygroscopic solid
- hydrates
- tetra-, hexa-, and decahydrates
- role
- intermediate in chromium extraction
- production_method
- roasting chromium ores with sodium carbonate at ~1100 °C
- hazard
- carcinogenic, corrosive, severe eye damage
Lore & Background
Sodium chromate is obtained on a vast scale by roasting chromium ores in air in the presence of sodium carbonate at around 1100 °C. This process converts chromium into a water-extractable form, leaving behind iron oxides. Calcium carbonate is typically included to improve oxygen access and keep silicon and aluminium impurities insoluble. For lab and small scale preparations, a mixture of chromite ore, sodium hydroxide, and sodium nitrate reacting at lower temperatures may be used.
Reader's Guide
Sodium chromate is central to the industrial production of chromium from its ores. It 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. Beyond metallurgy, it is used as a corrosion inhibitor in the petroleum industry, a dyeing auxiliary in textiles, and a diagnostic pharmaceutical for determining red blood cell volume. In organic chemistry, it serves as a strong oxidizer, converting primary alcohols to carboxylic acids and secondary alcohols to ketones. As a Cr(VI) compound, it is carcinogenic, corrosive, and exposure may cause severe eye damage, impaired fertility, heritable genetic damage, and harm to unborn children.
Did You Know?
- Sodium chromate is a yellow hygroscopic solid that can form tetra-, hexa-, and decahydrates.
- It is produced on a vast scale by roasting chromium ores with sodium carbonate at around 1100 °C.
- It converts to sodium dichromate when treated with acids, and further acidification yields chromium trioxide.
- It is used as a diagnostic pharmaceutical to determine red blood cell volume.
More in Sodium Compounds 1-24
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