Sodium dichromate

• Red chromate of sodium
• Double Chromate sodium
• Natriumpyrochromat
• Sodium bichromate

Orange red, odorless, hygroscopic crystalline needles

Fixed

2.52 g · cm -3

356.7 ° C

400 ° C ( decomposition)

Very well in water ( 2355 g · l-1 at 20 ° C)

Risk

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Sodium dichromate ( VI) ( Na2Cr2O7 ) is a sodium salt of dichromic ( H2Cr2O7 ) and is one of the chromates. It crystallizes as a dihydrate ( Na2Cr2O7 · 2 H2O, molar mass 297.99 g / mol).

Production and representation

(III ) oxides is sodium dichromate on a large scale from ores with chrome won. The ore is treated with base (typically sodium carbonate) at elevated temperatures in the presence of oxygen:

Reactions in aqueous solution

The aqueous solution is acidic and it sets itself a dichromate - chromate equilibrium. Since the chromate anion ( CrO42 - ) is a strong base, the anion for the most part as Hydrogenchromat ( HCrO4 ) is present:

Since the autoionization of water always OH - ions and H ions (or H3O ions) are available to provide a more equilibrium reactions:

Use

It finds frequent use in the metal surface treatment (corrosion inhibitor), for wood impregnation and used among other things for the production of anti-corrosive pigments, with a balance of sodium dichromate and sodium chromate is formed. Furthermore, it is used in the chemical industry as oxidising agent for organic synthesis processes, for example for the synthesis of anthraquinone.

Safety

Sodium dichromate is very toxic, inflammable and hazardous to the environment. It can cause cancer, cause heritable genetic damage, affect fertility and cause harm to the unborn child. Before working with sodium dichromate should be consulted in any case the safety data sheet and all necessary precautions are taken.