Sodium dichromate - Na2Cr2O7

What is Sodium dichromate?

Na₂Cr₂O₇ is an inorganic compound with chemical name Sodium dichromate. It is also called Bichromate of soda or Disodium dichromate or Sodium dichromate (VI). It is a powerful oxidizing agent and highly corrosive.

Bichromate of soda is a red to red-orange crystalline solid. It is odourless and dissolves in water, methanol as well as ethanol. It is widely used as a corrosion inhibitor. On heating it liberates toxic chromium fumes.

Properties of Sodium dichromate – Na₂Cr₂O₇

Sodium dichromate structure – Na₂Cr₂O₇

Na₂Cr₂O₇ Uses (Sodium dichromate)

• Sodium dichromate is a primary material in the manufacturing of chromium chemicals.
• Used as textile dyes.
• Used in water treatment.
• Used in leather tanning.
• Used as a catalyst.
• Used as an oxidising agent in the manufacturing of synthetic organic chemicals.
• Used in the refining of petroleum.
• Used in metal treatments such as electro-engraving of copper.
• Used in Colorimetry experiment to determine the amount to copper.
• Used as an insecticide and fungicide.
• Used as a colourant in glass.

Production of Sodium dichromate

On a large scale, Disodium dichromate is obtained from ores that contain chromium(III) oxides.

Step 1: Fusing the ore with a base such as sodium carbonate

Step 2: Maintain a temperature at around 1000 °C

Step 3: Conduct the above two steps in the presence of air which is the source of oxygen. The reaction is as follows:

2Cr₂O₃ + 4Na₂CO₃ + 3O₂ → 4Na₂CrO₄ + 4CO₂

The above steps solubilize the chromium and allows its extraction in the hot water. The other components present in the ore are poorly soluble hence acidification of the resulting aqueous extract with the help of carbon dioxide or sulfuric acid produces dichromate.

2Na₂CrO₄ + 4CO₂ + H₂O → Na₂CrO₇ + 2NaHCO₃

2Na₂CrO₄ + H₂SO₄ → Na₂CrO₇ + Na₂SO₄ + H₂O

With the process of crystallization the dichromate is extracted as dihydrate.

Health hazards

Inhalation of dust or mist of Sodium dichromate (VI) causes respiratory irritation which resembles asthma and nasal septal perforation may occur. Swallowing causes diarrhea, and vomiting. When exposed to eyes and skin it results in local irritation and dermatitis.

It is a non-combustible compound but increase combustion of other compounds. It can explode and catch fire when comes in contact with combustible substances.

Learn more about the Structure, physical and chemical properties of Na₂Cr₂O₇ from the experts at BYJU’S.