Sodium dichromate

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Sodium dichromate
Names
IUPAC name
Sodium dichromate
Systematic IUPAC name
Bichromate of soda
Celcure
Chromic acid disodium salt
Disodium dichromate
Natriumdichromat
Properties
Na2Cr2O7 (anhydrous)
Na2Cr2O7· 2H2O
Molar mass 261.97 g/mol (anhydrous)
298.00 g/mol (dihydrate)
Appearance Dark orange solid
Odor Odorless
Density 2.52 g/cm3
Melting point 356.7 °C (674.1 °F; 629.8 K)
Boiling point 400 °C (752 °F; 673 K) Decomposes
73 g/100 ml (25 °C)
Solubility Soluble in ethanol, methanol
Solubility in methanol 51.32 g/100 ml (19.4 °C)
Hazards
Safety data sheet Sigma-Aldrich (dihydrate)
Related compounds
Related compounds
Potassium dichromate
Ammonium dichromate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Sodium dichromate is the inorganic compound with the formula Na2Cr2O7, commonly encountered as dihydrate.

Properties

Chemical

Sodium dichromate can be used along with sulfuric acid in the Jones oxidation to oxidize primary alcohols to aldehydes, and secondary alcohols to ketones.

Physical

Sodium dichromate is an orange solid, hygroscopic and soluble in water and alcohols.

Availability

Chemical suppliers generally have it in their stock, at various purities.

Preparation

Sodium dichromate can be produced from stainless steel from dinnerware or cooking implements, which contains a minimum of 10.5% chromium by mass. First, the entire piece of stainless steel is dissolved in conc. hydrochloric acid. The resulting solution should be dark green due to the chromium(III) ion. Sodium carbonate (not sodium hydroxide) is added to the solution to neutralize all remaining acids and precipitate a mixture of iron and chromium hydroxides, which are then filtered and washed. The washed mixture is mixed with sodium hypochlorite solution, which will oxidize the chromium(III) ions to chromate(CrO42-) ions, bringing them into solution as sodium chromate. Once the yellow filtrate is collected, a strong acid can be added to reduce the pH of the solution, producing a solution of sodium dichromate.

Another route involves melting a mixture of sodium hydroxide with chromium(III) oxide, with sodium nitrate.

Projects

Handling

Safety

Sodium dichromate, like all other hexavalent chromium compounds, is highly toxic and carcinogenic on ingestion or inhalation. Handling it can cause dermatitis, and it could also be absorbed through the skin in small amounts, usually if wet. Always wear gloves and goggles when handling it, and a dust mask or respirator when handling it as a powder to avoid inhalation of it, which could be fatal.

Storage

Sodium dichromate should be kept in plastic containers, with a proper label and a hazard symbol. While glass containers can be used, it's recommended to avoid them, as if you drop the bottle on the floor, it will shatter and the dichromate will spread all over the lab floor, which required decontamination.

Disposal

Sodium dichromate can be reduced with ascorbic acid to the less harmful chromium(III). Other reducing agents, such as sodium/potassium/ammonium sulfite/thiosulfate/metabisulfite can be used.

References

Relevant Sciencemadness threads