What Is Sodium Dichromate Definition Formula Preparation Reactions and Uses
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.
The first step is to fuse the ore with a base such as sodium carbonate.
Next, maintain a temperature around 1000 °C.
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:
Metallic Finish - it helps to prevent corrosion, making it easier to clean the metallic surfaces and allows the paint to stick.
Organic products - used as oxidisers for the production of vitamin K and wax.
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.
Ceramics - used to produce coloured glass and ceramic glaze.
Textiles - used as a mordant in the acidic dyes to improve colour-fast properties.
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.
FAQs on Sodium Dichromate Structure Properties Reactions and Applications
1. What is sodium dichromate?
Sodium dichromate is an inorganic compound with the formula Na2Cr2O7 that contains the dichromate ion (Cr2O72-) and is a strong oxidizing agent. It usually appears as an orange crystalline solid and is highly soluble in water. In aqueous solution, it exists in equilibrium with the chromate ion depending on pH. Sodium dichromate is widely used in organic oxidation reactions, leather tanning, pigments, and corrosion inhibition.
2. What is the chemical formula and molar mass of sodium dichromate?
The chemical formula of sodium dichromate is Na2Cr2O7 and its molar mass is approximately 261.97 g/mol (for the anhydrous form). The molar mass is calculated as:
- Na: 22.99 × 2 = 45.98 g/mol
- Cr: 52.00 × 2 = 104.00 g/mol
- O: 16.00 × 7 = 112.00 g/mol
3. What is the oxidation state of chromium in sodium dichromate?
The oxidation state of chromium in sodium dichromate is +6. In the dichromate ion Cr2O72-:
- Oxygen has an oxidation state of −2.
- Total oxygen contribution = 7 × (−2) = −14.
- Overall charge of ion = −2.
2x − 14 = −2 → 2x = +12 → x = +6.
4. Is sodium dichromate an oxidizing agent?
Yes, sodium dichromate is a strong oxidizing agent, especially in acidic solution. In acidic medium, the dichromate ion is reduced from Cr6+ to Cr3+. A common half-reaction is:
Cr2O72- + 14H+ + 6e- → 2Cr3+ + 7H2O
- It oxidizes alcohols to aldehydes, ketones, or carboxylic acids.
- It is widely used in redox titrations and organic synthesis.
5. What is the difference between sodium dichromate and potassium dichromate?
The main difference between sodium dichromate and potassium dichromate is the cation present: Na2Cr2O7 contains sodium ions, while K2Cr2O7 contains potassium ions. Key differences include:
- Sodium dichromate is more soluble in water than potassium dichromate.
- Both contain the same dichromate ion (Cr2O72-).
- Both act as strong oxidizing agents in acidic medium.
6. How is sodium dichromate prepared industrially?
Sodium dichromate is prepared industrially by roasting chromite ore with sodium carbonate in the presence of air. The main steps are:
- Roasting: 4FeCr2O4(s) + 8Na2CO3(s) + 7O2(g) → 8Na2CrO4(s) + 2Fe2O3(s) + 8CO2(g)
- Conversion of sodium chromate to sodium dichromate by acidification:
2CrO42- + 2H+ → Cr2O72- + H2O
7. What happens when sodium dichromate is dissolved in water?
When sodium dichromate dissolves in water, it dissociates into sodium ions and dichromate ions: Na2Cr2O7(s) → 2Na+(aq) + Cr2O72-(aq). In aqueous solution:
- The solution appears orange due to the dichromate ion.
- It is in equilibrium with the chromate ion depending on pH.
- Acidic conditions favor dichromate (orange), while basic conditions favor chromate (yellow).
8. What is the chromate–dichromate equilibrium?
The chromate–dichromate equilibrium is the pH-dependent interconversion between CrO42- and Cr2O72-. The equilibrium reaction is:
2CrO42- + 2H+ ⇌ Cr2O72- + H2O
- In acidic solution: equilibrium shifts right (orange dichromate).
- In basic solution: equilibrium shifts left (yellow chromate).
9. What are the uses of sodium dichromate?
Sodium dichromate is mainly used as a strong oxidizing agent in industry and laboratories. Major uses include:
- Manufacture of chromium compounds and pigments
- Oxidation of alcohols in organic chemistry
- Leather tanning processes
- Corrosion inhibition and metal finishing
10. Is sodium dichromate hazardous?
Yes, sodium dichromate is highly toxic and carcinogenic because it contains hexavalent chromium (Cr6+). Key hazards include:
- Strong oxidizer that can cause burns
- Toxic if inhaled or ingested
- Environmental pollutant harmful to aquatic life
