Sodium Dichromate

Sodium dichromate or Na2Cr2O7 is an orange to red-coloured, crystalline, and inorganic compound which emits toxic chromium fumes on heating. Sodium dichromate is highly corrosive in nature and is a strong oxidizing agent. This substance is usually used to produce other chromium compounds but is also used for drilling muds, metal treatments, wood preservatives, production of dyes and organic chemicals, and as a corrosion inhibitor. In this article, we will learn about sodium dichromate in detail like the sodium dichromate reaction, sodium dichromate chemical formula, its uses, properties, density, and structure. Let us first learn about what is sodium dichromate or Na2Cr2O7 .

What is Sodium Dichromate?

Sodium dichromate or Na2Cr2O7 is an inorganic compound. It is also known as bichromate of soda, disodium dichromate, or sodium dichromate (VI). It is known to be a powerful oxidizing agent and is highly corrosive.

Sodium dichromate is a red to reddish-orange crystalline solid. It is odourless and dissolves in water, methanol and ethanol. It is commonly used as a corrosion inhibitor. On heating, it liberates chromium fumes that are toxic in nature.

Properties of Sodium Dichromate

Sodium Dichromate Structure

Sodium dichromate structure is shown below:

Production of Sodium Dichromate

On a larger scale, sodium dichromate is obtained from ores which contain chromium (III) oxides. Let us have a look at the Na2Cr2O7  reaction and how it is produced.

1. The first step is to fuse the ore with a base such as sodium carbonate.

2. Next, maintain a temperature around 1000 °C.

3. Then, conduct the above two steps in the presence of air that is the source of oxygen. The reaction is given below:

2Cr2O3 + 4Na2CO3 + 3O2 ---> 4Na2CrO4 + 4CO2 

These steps solubilize chromium and allow it to extract in the hot water. The other components present in the ore are poorly soluble and therefore, acidification of the resulting aqueous extract by utilizing carbon dioxide or sulfuric acid helps to produce dichromate. The reaction is as follows:

2Na2CrO4 + 4CO + H2O ---> Na2CrO7 + 2NaHCO3

2Na2CrO4 + H2SO4 ---> Na2CrO7 + Na2So4 + H2O

Using the process of crystallization, dichromate is extracted as a dihydrate.

Sodium Dichromate Uses

Apart from its importance for the production of other chromium products, sodium dichromate also has many uses as an ingredient in the production of the following materials:

1. Metallic Finish - it helps to prevent corrosion, making it easier to clean the metallic surfaces and allows the paint to stick.

2. Organic products - used as oxidisers for the production of vitamin K and wax.

3. Pigments - used in making inorganic chromate pigments where it produces a range of light-stable colours. Some grades of chromate are used for the prevention of corrosion in undercoats and primers.

4. Ceramics - used to produce coloured glass and ceramic glaze.

5. Textiles - used as a mordant in the acidic dyes to improve colour-fast properties.

6. Used in the chromium sulphate production.

Health Hazards of Sodium Dichromate

Inhaling the dust or mist of sodium dichromate (VI) can cause respiratory irritation that resembles asthma and nasal septal perforation. Swallowing it leads to diarrhoea, and vomiting. When it is exposed to eyes and skin it results in dermatitis and local irritation.

Sodium dichromate is a non-combustible compound but increases the combustion of other compounds. It can explode and catch fire whenever it comes in contact with other combustible substances.